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PostPosted: Fri Sep 28, 2018 1:10 am 
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Joined: Thu Sep 13, 2018 7:32 pm
Posts: 2
Location: London, UK
Hi guys! I’m new to this forum; I’d like to say first off that as my first venture into studio building I appreciate any advice you may have for me and am open to all suggestions. Due to budget limitations I am planning to do all design myself, and have my builder friend do the work (I’ll also help). I’m also open to any UK based studio consultants that I can afford to give me a rough idea/plan of best practice for the room design. Nothing other than enquiries have been done so far.

ROOM PURPOSE (OVERVIEW):

> This room will be for practicing, recording and mixing music: Guitars (acoustic and electric)/bass/keys/vox/small drum kit- by myself only.

> All instruments will likely be recorded one at a time; I’ll never have a “full band” playing in this room.

> I plan to have a SMALL/basic kit in there (No Bonham!) I know it’s not adequate for drum recording; I’ll close-mic and add nice room/FX in post ;)

Basically, the studio is never going to be THAT loud. My garden is also pretty quiet; I’ll never have issues with noise coming into the studio. Both neighbours are cool; elderly lady on the left will most likely not hear anything, on the right they are further from the garage and will have no issue I’m sure. I just want a space that I can record in late at night that is not too noisy outside.


Also: I am making real world realistic choices with this studio. The space it what it is, and on my limited budget, after looking at lots of alternative options, the best choice is still to use this existing garage structure as my room. I’ve been told: It’s too small and the dimensions are not ideal for mixing/recording blah blah blah, but it is what it is, and I plan to do the best I can with it, within my budget.


*Existing structure* Single Car Brick Garage. (See pictures)

> Floor: Concrete
> Window: old timber framed window (to replace)
> Roof: Corrugated roof (not asbestos) (to replace) - supported by timber beams - Going to keep the strange pitch of the roof as I hope it will reduce room modes.
> walls: brick, single skin & pebble dash rendering on outside. A second layer of support bricks creates thin pillar in the middle and in corners.
> Doors: Two large wooden garage doors (to replace by bricking up and adding 2 door -inner & outer- system.)
> Electrics: Double wall socket and light installed. New Board to go in (Awaiting quotes) Thinking of mostly surface mounted power and lights.


Some questions:

Roof

> New roof needs to be installed. Should the rafters be cut into the walls? or is it ok to mount to the walls as some of the existing smaller beams have been in the pics? (I doubt it)

Should I use deeper rafters? I’m thinking I’ll use the 2 existing rafters that have been cut into the brick but add new additional beams to support the new roof.

How many layers of ply for the new roof would you suggest? I was thinking 3.

Is it worth putting some sort of Tecsound membrane in-between one of the layers?

Using the clip system, I plan to attach the rock wool into the roof cavities between beams, then resilient bar off the rafters connecting to the clips and drywall.



Walls/Ceiling

> As I’m trying to maximise space, I got some quotes for a Isomax/Genie clip system. £3k for all walls and ceiling. I don’t think I can afford that much on the entire system, so I was thinking of just putting the clip system on the ceiling as that is really the dimension that needs maximising (2.4m high at lowest end). If I build a standard inner leaf (timber frame >rock wool >Plasterboard green glue> plasterboard) it will be cheaper and I don’t mind losing the space, I’ll probably get better isolation too. I’m assuming that it will be fine to combine 2 methods? i.e. decoupling system on the ceiling to maximise height and the walls to be standard Frame/Drywall Green glue. The walls and ceiling won’t actually touch.

I assume that I don’t actually need to build a timber frame against the existing brick walls (Outer leaf) but simply need to work out what I can use to hold the rock wool against this outer skin. Anyone have any suggestions? Rod’s book doesn’t exactly go in to detail regarding existing brick walls.



Floor

> From what I have read here and in Rod’s book, it appears that my concrete floor is fine. I was thinking of adding some sort of rubber membrane and then laminate flooring on top. Any thoughts?


Doors

> I believe my best option on a budget for doors is to get 2 internal, heavy duty fire doors for the inner and outer door and use strip seals on the edges.


Windows

> There is an existing window and Building regs say that I have to retain a window that can be opened in an emergency, so I have to keep the window. I’m struggling to find suitable new windows. I suppose I’m just going to go with a standard triple glazed UPVC window on the outside and same on the inside. I’m investigating a thin line window with thick glazing on the inside. Any suggestions?


Ventilation/HVAC

> Still investigating this. I’m planning on getting a small electric heater on the wall. For ventilation I’ll more than likely be fitting the standard type of ventilation. I’m wondering, in regard to A/C can I get away with a smaller unit as I’ll be the only one in the room (most of the time) ?




Additional concerns:

I read that it is better to connect the stud frame to the concrete floor and the ceiling. Fair enough. However, if the roof rafters connect to the walls and the inner leaf stud connects to the ceiling, surely the inner leaf is now connected to the walls? I can’t see any other way though. Maybe as it is a 2nd-hand connection the vibration transference is reduced though?

And, if 2 walls are decoupled from each other and only touching via sealant, what happens when you fit timber bass traps to both walls in a corner, is that not just connecting the walls together?


Tecsound VS Green glue. I’ve read numerous posts where folks have asked this question on GS and the like. But most of the posts turn bad pretty quick and into a mud-slinging match of what system has actual proven results after testing. Green glue has the support of many and I assume this is good stuff. But how does this “Tecsound” LINK perform in comparison? It’s much easier to fit and hence more attractive to me. If it is a huge difference to GG I will consider, but I’m just wondering if anyone has real world experience with both?

*Images attached* the first 5 images are taken from the sketch up model I have created to base my plan on. the rest are photos of the existing garage.


I’m sure I’ve missed some points but can update the post… I really appreciate any feedback/suggestions that anyone can offer on this. If you would like me to add any additional information, please ask. I’m still feeling really daunted by this project and kinda not sure where to begin ;)

Cheers,

Sam.


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PostPosted: Fri Sep 28, 2018 3:51 am 
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Joined: Thu Aug 21, 2008 10:17 am
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Location: Santiago, Chile
Hi there Sam, and Welcome to the forum! :)

Quote:
This room will be for practicing, recording and mixing music:
Those are rather different acoustic needs. We'll get into that later, but basically they have mutually exclusive acoustic requirements. The solution is variable acoustic panels that can change the acoustic response of the room.

Quote:
Guitars (acoustic and electric)/bass/keys/vox/small drum kit .... Basically, the studio is never going to be THAT loud.
I beg to disagree! :) Even a "small" drum kit is loud. Easily 110 dB when played normally, likely 115, perhaps more if you are heavy handed. That's loud. Don't take this negatively, but drummers almost always way underestimate just how loud they are.

Quote:
My garden is also pretty quiet;
In other words, your loud drums inside will be easily heard outside, because outside is quiet... :)

Quote:
I’ll never have issues with noise coming into the studio.
So there is nothing in the UK that could trash your recording sessions? No thunder, rain, hail, or wind? No aircraft or helicopters flying over? No sirens from ambulances / police / fire engines? No trains? No cars arriving / leaving / driving past? No dogs barking outside? And nothing in the house either, such as water running in pipes, fans, pumps and other motors, people walking on floors, doors closing, people talking, vacuum cleaners, washing machine, radio, TV, furnace.... There's hundreds of possible sounds that could destroy a good recording, if they get into the mics in your control room. Are you CERTAIN that your room will not get any of that? :)

Quote:
...they are further from the garage and will have no issue I’m sure.
Your current neighbors might be fine with your noise, and also quite themselves, but what happens if they move out and others move in? There are also LEGAL requirements that you must meet, in terms of noise level, regardless of how nice your neighbors are.

Quote:
I just want a space that I can record in late at night that is not too noisy outside.
Those legal requirements that I mentioned above usually allow a fairly high noise level during the day, but a much lower one at night. You better check with your local municipality to find out just what the regulations and bylaws say.

Quote:
I am making real world realistic choices with this studio. The space it what it is, and on my limited budget, after looking at lots of alternative options, the best choice is still to use this existing garage structure as my room. I’ve been told: It’s too small and the dimensions are not ideal for mixing/recording blah blah blah, but it is what it is, and I plan to do the best I can with it, within my budget.
And that's perfectly fine! :thu: As long as you are aware of the limitations, and are happy about that, then that's fine! Many forum members have built studios in very small spaces. John has even designed one inside a shipping container! It is possible to build decent studios in small spaces. However, to be aware that the smaller it is, the harder it is to treat acoustically. Very small rooms require tons of treatment. So much so, that the treatment takes up a huge chunk of the available space. Once again, as long as you are OK with that, then no problem!

Having a small room is one hell of a lot better than having no room at all!


Quote:
> Floor: Concrete
:thu: Good start!

Quote:
> Window: old timber framed window (to replace)
Great! Replace with non-operable (fixed pane) laminated glass that has the same density as the rest of the outer leaf.

Quote:
> Roof: Corrugated roof (not asbestos) (to replace)
Good! Replace with something that has the same surface density as the walls.

Quote:
Going to keep the strange pitch of the roof as I hope it will reduce room modes.
Ummm.... you seem to be misunderstanding modes. You do not want FEWER modes. You want MORE modes! You want as many as you can get!

This is a common misconception, and I wrote a rather long post about that a while ago, so I'll just repeat it here. Take your time to work through it. I tried to keep it simple to understand, but some of the concepts do take a while to sink in.

Basically, when you talk about room modes, you are talking about "room ratios".

Room ratios is a whole major subject in studio design. It works like this: The walls of your studio create natural resonances in the air space between them, inside the room. (This is totally different from the MSM resonance of the walls themselves: this is all about what happens INSIDE the ROOM, not what happens inside the walls. Two totally different things.)

So you have resonant waves inside the room. We call those "standing waves" or "room modes". Those "modes" (resonances) occur at very specific frequencies that are directly related to the distances between the room boundaries (walls, floor, ceiling). They are called "standing waves" because they appear to be stationary inside the room: they are not REALLY stationary, since the energy is still moving through the room. But the pressure peaks and nulls always fall at the exact same points in the room each time the wave energy passes, so the "wave" seems to be fixed, static, and unmoving inside the room. If you play a pure tone that happens to be at the exact frequency of one of the "modes", then you can physically walk around inside the room and experience the "standing" nature of the wave: you will hear that tone grossly exaggerated at some points in the room, greatly amplified, while at other points it will sound normal, and at yet other points it will practically disappear: you won't be able to hear it at all, or you hear it but greatly attenuated, very soft.

The peaks and nulls fall at different places in the room for different frequencies. So the spot in the room where one mode was deafening might turn out to be the null for a different node.

Conversely, if you have a mode (standing wave) that forms at a specific frequency, then playing at a slightly different frequency might show no mode at all: for example, if a tone of exactly 73 Hz creates a standing wave that is clearly identifiable as you walk around the room, with major nulls and peaks, then a tone of 77 Hz might show no modes at all: it sounds the same at all points in the room. Because there are no natural resonances, no "room modes" associated with that frequency.

That's the problem. A BIG problem.

Of course, you don't want that to happen in a control room, because it implies that you would hear different things at different places in the room, for any give song! At some places in the room, some bass notes would be overwhelming, while at other places the same notes would be muted. As you can imagine, if you happen to have your mix position (your ears) located at such a point in the room, you'd never be able to mix anything well, as you would not be hearing what the music REALLY sounds like: you would be hearing the way the room "colors" that sound instead. As you subconsciously compensate for the room modes while you are mixing, you could end up with a song that sounds great in that room at the mix position: the best ever! But it would sound terrible when you played it at any other location, such as in your car, on your iPhone, in your house, on the radio, at a club, in a church, etc. Your mix would not "translate".

And you also don't want major modal issues in a tracking room, for similar reasons: As an instrument plays up and down the scale, some notes will sound louder than others, and will "ring" longer. The instrument won't sound even and balanced.

OK, so now I have painted the scary-ugly "modes are terrible monsters that eat your mixes" picture. Now lets look at that a bit more in depth, to get the real picture, and understand why they look bad, but aren't so bad in reality.

So let's go back to thinking about those room modes (also called "eigenmodes" sometimes): remember I said that they occur at very specific frequencies, and they are very narrow? This implies that if you played an E on your bass guitar, it might trigger a massive modal resonance, but then you play either a D or an F and there is no mode, so they sound normal. Clearly, that's a bad situation. But what if there was a room mode at every single frequency? What if there was one mode for E, a different mode for D and yet another one for F? In that case, there would be no problem, since all notes would still sound the same! Each note would trigger its own mode, and things would be happy again. If there were modes for every single frequency on the spectrum, and they all sounded the same, then you could mix in there with no problems!

And that's exactly what happens at higher frequencies. Just not at low frequencies. Because of "wavelength"...

It works like this: remember I said that modes are related to the distance between walls? It's a very simple relationship. Remember I said the waves are "standing" because the peaks and nulls occur at the same spot in the room? In simple terms, for every frequency where a wave fits in exactly between two walls, then there will be a standing wave. And also for exactly twice that frequency, since two wavelengths of that note will now fit. And the same for three times that frequency, since three full waves will now fit in between the same walls. Etc. All the way up the scale.

So if you have a room mode at 98 Hz in your room, then you will also have modes at 196 Hz (double), 294 (triple), 392 (x4), 490(x5), 588(x6), 686(x7) etc., all the way up. If the very next mode in your room happened to be at 131 Hz, then there would also be modes at 262 Hz(x2), 393(x3), 524(x4), 655(x5), etc.

That's terrible, right? There must be thousands of modes at higher frequencies!!! That must be awful!

Actually, no. That's a GOOD thing. You WANT lots of modes, for the reasons I gave above: If you have many modes for each note on the scale, then the room sounds the same for ALL notes, which is what you want. It's good, not bad.

But now let's use a bit of math and common sense here, to see what the real problem is.

If your room has a mode at 98Hz, and the next mode is at 131 Hz, that's a difference of 32%! 98 Hz is a "G2". So you have a mode for "G2". but your very next mode is a "C3" at 131Hz. That's five notes higher on the scale: your modes completely skip over G2#, A2, A2#, and B2. No modes for them! So those four notes in the middle sound perfectly normal in your room, but the G2 and C3 are loud and long.

However, move up a couple of octaves: ...

There's a harmonic of your 98Hz mode at 588 Hz, and there's a harmonic of your 131 Hz mode at 524 Hz. 524 Hz is C5 on the musical scale, and 588 Hz is a D5. They are only two notes apart! Not five, as before.

Go up a bit more, and we have one mode at 655 and another at 686. 655 is an E5, and 686 is an F5. they are adjacent notes. Nothing in between! We have what we want: a mode for every note.

The further up you go, the closer the spacing is. In fact, as you move up the scale even higher, you find several modes for each note. Wonderful!

So at high frequencies, there is no problem: plenty of modes to go around and keep the music sounding good.

The problem is at low frequencies, where the modes are few and far between.

The reason there are few modes at low frequencies is very simple: wavelengths are very long compared to the size of the room. At 20 Hz (the lower limit of the audible spectrum, and also E0 on the organ keyboard), the wavelength is over 56 feet (17m)! So your room would have to be 56 feet long (17 meters long) in order to have a mode for 20 Hz.

Actually, I've been simplifying a bit: it turns out that what matters is not the full wave, but the half wave: the full wave has to exactly fit into the "there and back" distance between the walls, so the distance between the walls needs to be half of that: the half-wavelength. So to get a mode for 20 Hz, your room needs to be 56 / 2 = 28 feet long (8.5M) . Obviously, most home studios do not have modes at 20 Hz, because there's no way you can fit a 28 foot (eight meter) control room into most houses!

So clearly, the longest available distance defines your lowest mode. If we take a hypothetical dimensions as an example (typical of a very small home studio), and say the length of the control room is 13 feet (4m), the width is 10 feet (3m), and the height is 8 feet. (2.5M) So the lowest mode you could possibly have in that room, would be at about 43 Hz (fits into 13 feet or 4M perfectly). That's an "F1" on your bass guitar.

The next highest mode that you room could support is the one related to the next dimension of the room: In this case, that would be width, at 10 feet / 3M. That works out to 56.5 Hz. That's an "A1#" on your bass guitar. Five entire notes up the scale.

And your third major mode would be the one related to the height of the room, which is 8 feet /2.5M, and that works out to 71 Hz, or C2# on the bass guitar. Another four entire notes up the scale.

There are NO other fundamental modes in that room. So as you play every note going up the scale on your bass guitar (or keyboard), you get huge massive ringing at F, A# and C#, while all the other notes sound normal. As you play up the scale, it goes "tink.tink.tink.BOOOOM.tink.tink.tink.tink.BOOOOOM.tink.tink.tink.BOOOOOM.tink.tink...."

Not a happy picture.

There are harmonic modes of all those notes higher up the scale, sure. But in the low end, your modes are very few, and very far between.

So, what some people say is "If modes are bad, then we have to get rid of them". Wrong! What you need is MORE modes, not less. Ideally, you need a couple of modes at every single possible note on the scale, such that all notes sound the same in your room. In other words, the reverberant field would be smooth and even. Modes would be very close together, and evenly spread.

So trying to "get rid of modes" is a bad idea. And even if it were a good idea, it would still be impossible! Because modes are related to walls, the only way to get rid of modes is with a bulldozer! Knock down the walls... :shock:

That's a drastic solution, but obviously the only way to get a control room that has no modes at all, is to have no walls! Go mix in the middle of a big empty field, sitting on top of a 56 foot (17 M) ladder, and you'll have no modes to worry about.... 8) :roll:

:shot:

Since that isn't feasible, we have to learn to live with modes.

Or rather, we have to learn to live with the LACK of modes in the low end. As I said, the problem is not that we have too many modes, but rather that we don't have enough of them in the low frequencies.

Obviously, for any give room there is a point on the spectrum where there are "enough" modes. Above that point, there are several modes per note, but below it there are not.

There's a mathematical method for determining where that point is: a scientist called Schroeder figured it out, years ago, so it is now known as the Schroeder frequency for the room. Above the Schroeder frequency for a room, modes are not a problem, because there are are lots of them spaced very close together. Below the Schroeder frequency, there's a problem: the modes are spaced far apart, and unevenly. (The Schroeder frequency is a bit more complex than just that, since it also considers treatment, but this gives you an idea...)

So what can we do about that?

All we can do is to choose a "room ratio" that has the modes spaced out sort of evenly, and NOT choose a ratio where the modes are bunched up together. For example, if your room is 10 feet long and 10 feet wide and 10 feet high (3m x 3m x 3m), then all of the modes will occur at the exact same frequency: 56.5 Hz. So the resonance when you play an A1 on the bass, or cello, or hit an A1 on the keyboard, will by tripled! It will be three times louder. The nulls will be three times deeper. That's a bad situation, so don't ever choose room dimensions that are the same as each other.

You get the same problem for dimensions that are multiples of each other: a room 10 feet high (3m) by 20 feet wide (6m) by 30 feet long (9m) is also terrible. All of the second harmonics of 10 feet will line up with the 20 foot modes, and all of the third harmonics will line up with the 30 foot modes, so you get the same "multiplied" effect. Bad.

In other words, you want a room where the dimensions are mathematically different from each other, with no simple relationship to each other.

That brings up the obvious question: What ratio is best?

Answer: there isn't one! :)

Over the years, many scientists have tested many ratios, both mathematically and also in the real world, and come up with some that are really good. The ratios they found are named after them: Sepmeyer, Louden, Boner, Volkmann, etc. Then along came a guy called Bolt, who drew a graph showing all possible ratios, and he highlighted the good ones found by all the other guys, and predicted by mathematical equations, plus a few of his own: If you plot your own room ratio on that graph, and it falls inside the "Bolt area", then likely it is a good one, and if it falls outside the "Bolt area", then likely it is a bad one. Sort of.

So, there are no perfect ratios, only good ratios and bad ratios.

It is impossible to have a "perfect" ratio in a small room, simply because that would require enough modes to have one mode for every note on the musical scale, but that's the entire problem with small rooms! There just are not enough modes in the low end. So you can choose a ratio that spreads them a bit more this way or a bit more that way, but all you are doing is re-arranging deck chairs on the Titanic, in pleasant-looking patterns. The problem is not the location of the deck chairs; the problem is that your boat is sunk!: Likewise for your studio: the problem is not the locations of the modes: the problem is that your room is sunk. No matter what you do with the dimensions, you cannot put a mode at every note, unless you make the room bigger. It is physically impossible.

But that does not mean that your room will be bad. That's the common perception, and it is dead wrong.

All of this leads to the question you didn't ask yet, but are probably heading for: What can I do about it?

Here's the thing: Modes are only a problem if they "ring". The wave is only a problem if the energy builds up and up and up, with each passing cycle, until it is screaming, and then the "built up" energy carries on singing away, even after the original note stops. That's the problem. If you stop playing the A1 on your guitar, and the room keeps on playing an A1 for a couple of seconds, because it "stored" the resonant energy and is now releasing it, then that's a BIG problem! The room is playing tunes that never were in the original music! :shock:

If a mode doesn't ring like that, then it is no longer a major issue. (It is still an issue for other reasons, just not a major one....)

So how do you stop a mode? You can't stop it from being there. But you CAN stop it from "ringing". You can "damp" the resonance sufficiently that the mode dies away fast, and does not ring. You remove the resonant energy and convert it into heat: no more problem! In other words, it's not good if you own a large angry dog that barks all the time and bights your visitors, but it's fine to own a large angry dog with a muzzle on his mouth, so he cannot bark and cannot bight!

You do that with "bass trapping". A bass trap is like the dog muzzle. It doesn't get rid of the problem, but it does keep it under control. You use strategically placed acoustic treatment devices inside the room that absorb the ringing of the mode, then it cannot ring. There are several ways to do that, with different strategies, but the good news is that in most rooms it is possible to get significant damping on the modes, so that they don't ring badly, and don't cause problems. Note that bass trapping does not absorb the mode: it just absorbs the ringing. Some people don't understand this, and think that the bass trapping makes the modes go away: it doesn't. All it does is to damp them. The modes are still there, and still affect the room acoustics in other ways, but with good damping, at least they don't "ring" any more.

And that is the secret to making a control room good in the low end! Choose a good ratio to keep the modes spread around evenly, then damp the hell out of the low end, so modes cannot ring. It's that simple.

The smaller the room, the more treatment you need. And since those waves are huge (many feet long), you need huge bass trapping (many feet long/wide/high/deep). It takes up lots of space, and the best place for it is in the corners of the room, because that's where all modes terminate. If you want to find a mode in your room, go look for it in the corner: it will be there. All modes have a pressure node in two or more corners, so by treating the corners, you are guaranteed of hitting all the modes.

As I said, there is no single "best" ratio, but there are good ones. You can use a "Room Mode Calculator" to help you figure out which "good ones" are within reach of the possible area you have available, then choose the closest good one, and go with that. And stay away from the bad ones.

Arguably, Sepmeyer's first ratio is the "best", since it can have the smoothest distribution of modes... but only if the room is already within a certain size range. Other ratios might be more suitable if your room has a different set of possible dimensions. So there is no "best".

But that's not the entire story: So far, all the modes I have mentioned are only related to two walls across the room, opposite from each other. I mentioned modes that form along the length axis of the room (between the front and back wall), others that form along the width axis (between left and right walls), and others that form on the height axis (between floor and ceiling): Those are the easiest ones to understand, because they "make sense" in your head when you think about them. Those are called "axial modes", because they form along the major axes of the room: length axis, width axis, height axis.

However, there are also other modes that can form between four surfaces, instead of just two. For example, there are modes that can bounce around between all four walls, or between the front and back walls as well as the ceiling and floor: those are called "tangential modes". And there are other modes that can form between all six surfaces at once: they involve all four walls plus the ceiling and the floor. Those are called "oblique modes".

The complete set of modes in your room consists of the axial modes, plus the tangential modes, plus the oblique modes.

That's what a good room mode calculator (a.k.a. "room ratio calculator") will show you. There are bad calculators that only show you the axial modes, which is pretty pointless, and the good ones show you all three types.

Use one of these Room Ratio calculators to figure out the best dimensions for your room:

http://www.bobgolds.com/Mode/RoomModes.htm

http://amroc.andymel.eu/

Both of those are very good, and will help you to decide how best to build your room. They give you tons of information that is really useful to help figure out the best dimensions.

However, modes aren't that important, despite all the hype they get: Modes are one aspect of room design, but there are many more. It's wise to choose a ratio that is close to one of the good ones, or inside the Bolt area, but you do NOT need to go nuts about it! There's no need to nudge things around by millimeters or smalls fractions of an inch, hoping to get a "better" ratio. Just stay away from the bad ones, get close to a good one, and you are done. End of story.

----------

OK, that's the end of the "cut and paste" about modes. I hope that helps you get the idea why "Going to keep the strange pitch of the roof as I hope it will reduce room modes" is not necessary, or even good. If you want to keep the roof shape because you like it, or because your bylaws say you have to, or because you don't fell like building more brickwork to get it higher, then fine! But keeping the shape in order to try to reduce the modes, is not a good reason, if it it would work.

Quote:
> walls: brick, single skin & pebble dash rendering on outside.
:thu: So you have a decent floor (concrete slab) and decently massive outer-leaf walls. All you need to do to complete the outer-leaf shell, is to replace your roof with something that has similar surface density, and install doors and windows that also have similar surface density.

Quote:
> Doors: Two large wooden garage doors (to replace by bricking up and adding 2 door -inner & outer- system.)
:thu: Perfect!

Quote:
> Electrics: Double wall socket and light installed. New Board to go in (Awaiting quotes) Thinking of mostly surface mounted power and lights.
:thu:

There's one item you missed from your list, and it's a biggie! HVAC. Yes, you absolute do need that. No, it is not a luxury. It is just as necessary as having speakers in a control room, or mics in the live room. Without a proper HVAC system, you don't have a usable studio.

Quote:
> New roof needs to be installed. Should the rafters be cut into the walls? or is it ok to mount to the walls as some of the existing smaller beams have been in the pics? (I doubt it)
Your structural engineer will guide you there (yes, you need one of those too!) Depending on what type of roof you install, that will pretty much dictate how it is to be built. The most important point about your new roof is that it MUST have the same surface density a your walls. So you will need to use something very massive (heavy) that has roughly the same surface density as brick. I would suggest "beam and block" as a good possibility. Another option would be just to pour a concrete roof. A distant third would be to build it up from trusses and a very massive deck (multiple layers of OSB / plywood / fiber-cement board) with asphalt shingles as the final surface. But talk to your builder-friend, and also to your structural engineer, to see what that suggest. Listen to, and obey, your structural engineer! He is the ONLY person who is qualified to guide you on this! And since he will be the one signing the paperwork for your permit and inspection applications, it's on his head to get it right. If he doesn't get it right, then the roof will be on YOUR head! Literally.... :)

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Should I use deeper rafters? I’m thinking I’ll use the 2 existing rafters that have been cut into the brick but add new additional beams to support the new roof.
Once again your structural engineer is the only guy qualified to tell you that. You can look up things on span tables, and calculate masses and deflections and densities and things your self, for sure, but you will ALWAYS need a certified local structural engineer to confirm that your calculations are correct, and he will put his signature on the paperwork that you present in order to get your building permits, and your inspections.

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How many layers of ply for the new roof would you suggest? I was thinking 3.
See above. But don't guess! Do the math yourself: The absolute density of brick is about 2300 kg/m3. The absolute density of plywood is around 560 kg/m3, so call that about a quarter of the density of brick. So if your bricks are "standard" 102mm thick, then the surface density of those is about 230 kg/m2, roughly. To get the same surface density with plywood, it would have to be four times as thick (because plywood is one fourth the density), so that would be 400mm thick. Plywood usually comes in sheets that are 16mm, 19mm, or 25mm thick. Assuming you can get 25mm, you would need 400/25 = 16 layers. Not three layers, but sixteen layers. That would get you to the same surface density as that of your walls... :shock:

I'm sure you were not expecting that! But that's the sad truth. Assuming you want good isolation for your studio, the outer-leaf shell needs to have the same surface density all around. The entire "envelope" must have the same weight per square meter. Your isolation is only as good as the weakest part. So if you have great walls, a great floor, and great windows and doors, but a lousy roof, then the roof is the "weakest link". It sets the limit for your total isolation.

OK, so clearly is is unrealistic to do this with plywood, assuming that you want decent isolation. Hence my suggestion of "beam and block" for your roof. Look into it.

Now, so far I'm assuming that you have already figure out how much isolation you need, in terms of decibels. If you don't yet know that, then that's the very first things you need to do: buy a hand-held sound level meter (around US$ 100 for a decent one), and measure. The number you come up with here is what defines the entire construction of your studio! It is a VERY important number. So measure with care, think it through carefully, then decide on that number realistically.

OK, so let's say that you figure out you actually don't need so much isolation, an you can live with a very weak link up above you, built from 75mm of plywood ( three layers of 25mm). You COULD do that, yes, as long as you do the math to determine what ELSE you wold need to do, to get the isolation you need. You already know that you need an inner-leaf, in addition to the outer leaf, so there are ways of compensating for deficiencies in the outer leaf, by doing things differently in the inner-leaf. Yes. It can be done. But you need to do the math here: you need to use the equations for 2-leaf structures to figure out how to build your outer-leaf roof and inner-leaf ceiling such that together, AS A SYSTEM, they provide the isolation you need.

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Is it worth putting some sort of Tecsound membrane in-between one of the layers?
Yes. No. Maybe. Certainly. Absolutely not. Could be.... :) Sorry to be cryptic, but there's no way of answering that without first knowing how much isolation you need, and how you plan to get it. Your calculations will tell you how much MASS you need up there on the roof, but it won't tell you what brands and models of building materials to use. In fact, sound waves don't care at all! They are not snobbish, they can't read the price tags on your building materials, and they just don't care how much you paid for it. All the respond to is the mass of each leaf, and the air spring between them, and the damping inside. They don't care at all if you paid handsome prices for the mass and damping, or if you got it form the bargain shelves. So it's best to go with the least expensive materials that will do the job.

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Using the clip system, I plan to attach the rock wool into the roof cavities between beams, then resilient bar off the rafters connecting to the clips and drywall.
Ummmm.... this might seem a little harsh, but how on earth did you arrive at that solution, when you don't even know how much isolation you need? You are just guessing and hoping. Guessing and hoping is not a good way to build a studio. Instead, do the math. It's not that hard. It would be really sad if you invest all this money, and time, and effort, only to find that the room is no use because it doesn't isolate properly...
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> As I’m trying to maximise space, I got some quotes for a Isomax/Genie clip system. £3k for all walls and ceiling. I don’t think I can afford that much on the entire system, so I was thinking of just putting the clip system on the ceiling as that is really the dimension that needs maximising (2.4m high at lowest end). If I build a standard inner leaf (timber frame >rock wool >Plasterboard green glue> plasterboard) it will be cheaper and I don’t mind losing the space, I’ll probably get better isolation too. I’m assuming that it will be fine to combine 2 methods? i.e. decoupling system on the ceiling to maximise height and the walls to be standard Frame/Drywall Green glue. The walls and ceiling won’t actually touch.
Once again, you are basing your decisions on the wrong factors! As soon as you see yourself writing "I think..." and "I was thinking..." and "I'm assuming...." and "probably....", that should be raising major red flags! Never, ever base any part of your room design on guesses, assumptions, "think"'s or "probably"'s. Instead, do the math to be CERTAIN that you will get what you are needing.

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I assume that I don’t actually need to build a timber frame against the existing brick walls (Outer leaf) but simply need to work out what I can use to hold the rock wool against this outer skin. Anyone have any suggestions?
Put up your inner-leaf framing, then fill the entire cavity with the correct insinuation, then put the vapor barrier on (if applicable), then put the drywall (plasterboard) on. It's that simple. The vapor barrier (assuming that your building codes says that you need it) and the drywall will hold the insulation in place. Use semi-rigid batts to help ensure that everything stays nice and vertical, without slumping down.

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it appears that my concrete floor is fine.
:thu:

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I was thinking of adding some sort of rubber membrane and then laminate flooring on top. Any thoughts?
Use whatever underlay the laminate flooring manufacturer recommends! First choose the laminate that you want, then check the installation instructions. It will tell you how flat the slab must be (you might need to level it), and it will tell you exactly what types of underlay are approved for that specific flooring. Use the best one on the list. Don't skimp!

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> I believe my best option on a budget for doors is to get 2 internal, heavy duty fire doors for the inner and outer door and use strip seals on the edges.
You are on a very tight budget: don't by the doors... build them yourself. It's not that hard. And yes, you do need seals around the complete perimeter of each door: top, both sides, and the bottom. You need at least two such seals on each door, and three is better. For the threshold, drop-down door seals are very recommended. You will also need heavy duty hinges (not the normal flimsy ones used on typical house doors), and you will need more of them than you think: at least four per door (rather then the usual three), and maybe as many as six, if your doors are very heavy. You will also need automatic door closers, since the doors will be too heavy to close by hand, safely. Those also need to be the right type for the weight of the door.

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> There is an existing window and Building regs say that I have to retain a window that can be opened in an emergency, so I have to keep the window. I’m struggling to find suitable new windows
It's a pity that it has to be operable, as that reduces isolation. Oh well: if that's what the regulations say, then that's what you have to do! So you will need two windows, one for the outer leaf, one for the inner leaf, and each of them will have a single pane of thick laminated glass. Get units with heavy-duct hinges, multiple seals, and a good handle that locks down well, with the correct pressure on the seals.
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I suppose I’m just going to go with a standard triple glazed UPVC window on the outside and same on the inside.
So you don't want good isolation in the low end of the spectrum, where drums and bass guitars and keyboards live? :) Did you read the section in Rod's book on why triple-leaf is a really bad idea? Have you seen this diagram before?
Attachment:
2-leaf-3-leaf-4-leaf-STC-diagram--classic2-GOOD!!!.gif

That shows walls, not windows, but the same principle applies. Notice how a 2-leaf system is great for isolation, a 3-leaf system is worse, and a 4-leaf system is worse still. If you extrapolate, a 5-leaf system would be yet worse, and a 6-leaf would be REALLY lousy. You are proposing to put in a 6-leaf system... :shock: Two units, each with a triple-pane, makes for a total of 6 leaves...

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I’m investigating a thin line window with thick glazing on the inside. Any suggestions?
Just put in two ordinary windows, one for the inner leaf, one for the outer, each with a single pane of laminated glass of the correct density such that it matches the density of the leaf that it is in.

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> Still investigating this. I’m planning on getting a small electric heater on the wall. For ventilation I’ll more than likely be fitting the standard type of ventilation. I’m wondering, in regard to A/C can I get away with a smaller unit as I’ll be the only one in the room (most of the time) ?
Electric heaters do not dehumidify, and they do not cool, and they are very inefficient. They use a lot of electrical power, for very little actual heat. A small mini-split system is far, far more efficient (at least 300% more efficient, perhaps 400%, or more, depending on which one you buy), plus it also controls the humidity, and it also cools.

You can never get away with a unit that is smaller than you need, and you can never get away with one that is larger, either! Here too you need to do the math to figure out what size you NEED for your room. You need a certain cooling capacity, that is determined by your latent heat load and your sensible heat load, and you need a certain air flow rate, which is determined by the air volume in the room. When you do the math, you will come up with two answers: one tells you how many BTU/hr of heating/cooling capacity you need, and the other tells you how many CFM (Cubic Feet per Minute) of air you need to move. You do the calculations for the WORST CASE: a hot, humid day when all of your buddies are in there, jamming and sweating and having a great time, eating pizza, drinking beer, with a bunch of hear and effects boxes and computers and amps and lights and stuff. Then you choose a mini-split unit that just has the capacity to deal with that, when running on the very highest setting. You will mostly use a much lower setting, of course, when you are on your own, but the system has to be capable of handling the "worst-case" scenario.

You then also dimension your ducts and silencer boxes in accordance with those same numbers, to ensure that you are supplying enough fresh air to keep everyone alive inside the room, as well as keeping them comfortable, while also blocking enough sound so that you maintain the level of isolation that you need.

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I read that it is better to connect the stud frame to the concrete floor and the ceiling.
You read wrong! Yes, you certainly do attach the framing to the floor, but NEVER to the ceiling. That would create a direct flanking path between the inner-leaf walls and the outer-leaf roof. In other words, it would trash your isolation.


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surely the inner leaf is now connected to the walls?
Exactly. Very correct.

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I can’t see any other way though. Maybe as it is a 2nd-hand connection the vibration transference is reduced though
Nope! There is no connection at all. The walls sit on the floor, and the ceiling sits on the wall, and NONE of that touches the existing walls or roof. End of story.

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And, if 2 walls are decoupled from each other and only touching via sealant,
Why to you want to decouple your inner-leaf walls from each other? They are all part of the same system, so why would you want to do that?

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what happens when you fit timber bass traps to both walls in a corner, is that not just connecting the walls together?
Yup! And so what? :)

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Green glue has the support of many and I assume this is good stuff.
It also has a proven track record, and abundant test data from independent laboratories that show HOW it works and THAT it works, exactly as advertised. Never use an acoustic product that is not backed up by independent test data.

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But how does this “Tecsound” LINK perform in comparison?
Your link doesn't work...

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If it is a huge difference to GG I will consider, but I’m just wondering if anyone has real world experience with both?
I can't help you there. I only use and recommend materials and products that are backed up by real data. So I have never used the product you mentioned, and never recommended it for my customers. Those of my customers that have used Green Glue compound in their walls and ceilings, have never been disappointed with the results.

But there's another question here: Why do you think you will need Green Glue compound? :)

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the first 5 images are taken from the sketch up model I have created to base my plan on
Use the "perspective" view, not the "parallel" view, to show the place more realistically.

Summary: Your place has decent possibilities. It is small, yes, but feasible. But you need to plan it properly, and design it properly, starting out by measuring the sound levels, and deciding on how much isolation you need, in decibels. You cannot successfully design the isolation system for a studio if you do not yet know hoe much isolation you need. Once you have that number, then you can stat using the equations and doing the math to figure out what building materials you will need in order to get the isolation that you have defined. Once you have THAT in place, you can start designing the actual method and techniques for your two-leaf system. And once that part of the design is finished, you can move on to the HVAC and electrical design, then finally the acoustic treatment design for the room interior.


- Stuart -


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PostPosted: Wed Oct 03, 2018 9:16 pm 
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Joined: Thu Sep 13, 2018 7:32 pm
Posts: 2
Location: London, UK
Soundman2020 wrote:
Hi there Sam, and Welcome to the forum! :)


Hi Stuart, thanks so much for the warm welcome, and I really appreciate you taking the time to write the detailed response to my post. Sorry it's taken a while to respond, I've been away from a PC for a few days... Please see my comments to each point below.

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This room will be for practicing, recording and mixing music:
Those are rather different acoustic needs. We'll get into that later, but basically they have mutually exclusive acoustic requirements. The solution is variable acoustic panels that can change the acoustic response of the room.


> OK. Sounds good!

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Guitars (acoustic and electric)/bass/keys/vox/small drum kit .... Basically, the studio is never going to be THAT loud.
I beg to disagree! :) Even a "small" drum kit is loud. Easily 110 dB when played normally, likely 115, perhaps more if you are heavy handed. That's loud. Don't take this negatively, but drummers almost always way underestimate just how loud they are.


> I guess you are correct ;) I just meant that the levels will not reach that of a full band playing in there for example. Also, if live drums are too loud in the end, I'll simply use electronic kit to trigger samples. As you can see, I am winging it a bit because I have no idea how much isolation I need for drums as I have no drums and cannot measure them in the garage as is.

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My garden is also pretty quiet;
In other words, your loud drums inside will be easily heard outside, because outside is quiet... :)


> Also true.

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I’ll never have issues with noise coming into the studio.
So there is nothing in the UK that could trash your recording sessions? No thunder, rain, hail, or wind? No aircraft or helicopters flying over? No sirens from ambulances / police / fire engines? No trains? No cars arriving / leaving / driving past? No dogs barking outside? And nothing in the house either, such as water running in pipes, fans, pumps and other motors, people walking on floors, doors closing, people talking, vacuum cleaners, washing machine, radio, TV, furnace.... There's hundreds of possible sounds that could destroy a good recording, if they get into the mics in your control room. Are you CERTAIN that your room will not get any of that? :)


> Again, you are correct. I was alluding to the fact that once I have a airtight room within a room setup, I don't believe that external noise in my garden will play as big a role as people in less favourable locations. You might have heard that we get some rain sometimes though :lol:

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...they are further from the garage and will have no issue I’m sure.
Your current neighbors might be fine with your noise, and also quite themselves, but what happens if they move out and others move in? There are also LEGAL requirements that you must meet, in terms of noise level, regardless of how nice your neighbors are.


> Good points, taken on board. I'll find out the legal requirements.

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I just want a space that I can record in late at night that is not too noisy outside.
Those legal requirements that I mentioned above usually allow a fairly high noise level during the day, but a much lower one at night. You better check with your local municipality to find out just what the regulations and bylaws say.


> I will do this, thanks. I'll more than likely be respectful in the evening and track all my electric guitars through modelling devices (headphones) instead of amps, and save drum takes to the day/weekend.

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I am making real world realistic choices with this studio. The space it what it is, and on my limited budget, after looking at lots of alternative options, the best choice is still to use this existing garage structure as my room. I’ve been told: It’s too small and the dimensions are not ideal for mixing/recording blah blah blah, but it is what it is, and I plan to do the best I can with it, within my budget.
And that's perfectly fine! :thu: As long as you are aware of the limitations, and are happy about that, then that's fine! Many forum members have built studios in very small spaces. John has even designed one inside a shipping container! It is possible to build decent studios in small spaces. However, to be aware that the smaller it is, the harder it is to treat acoustically. Very small rooms require tons of treatment. So much so, that the treatment takes up a huge chunk of the available space. Once again, as long as you are OK with that, then no problem!

Having a small room is one hell of a lot better than having no room at all!


> Thanks, gives me some hope! :)


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> Floor: Concrete
:thu: Good start!


> Cool!

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> Window: old timber framed window (to replace)
Great! Replace with non-operable (fixed pane) laminated glass that has the same density as the rest of the outer leaf.


> OK.

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> Roof: Corrugated roof (not asbestos) (to replace)
Good! Replace with something that has the same surface density as the walls
.

> OK.

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Going to keep the strange pitch of the roof as I hope it will reduce room modes.
Ummm.... you seem to be misunderstanding modes. You do not want FEWER modes. You want MORE modes! You want as many as you can get!

This is a common misconception, and I wrote a rather long post about that a while ago, so I'll just repeat it here. Take your time to work through it. I tried to keep it simple to understand, but some of the concepts do take a while to sink in.

Basically, when you talk about room modes, you are talking about "room ratios".

Room ratios is a whole major subject in studio design. It works like this: The walls of your studio create natural resonances in the air space between them, inside the room. (This is totally different from the MSM resonance of the walls themselves: this is all about what happens INSIDE the ROOM, not what happens inside the walls. Two totally different things.)

So you have resonant waves inside the room. We call those "standing waves" or "room modes". Those "modes" (resonances) occur at very specific frequencies that are directly related to the distances between the room boundaries (walls, floor, ceiling). They are called "standing waves" because they appear to be stationary inside the room: they are not REALLY stationary, since the energy is still moving through the room. But the pressure peaks and nulls always fall at the exact same points in the room each time the wave energy passes, so the "wave" seems to be fixed, static, and unmoving inside the room. If you play a pure tone that happens to be at the exact frequency of one of the "modes", then you can physically walk around inside the room and experience the "standing" nature of the wave: you will hear that tone grossly exaggerated at some points in the room, greatly amplified, while at other points it will sound normal, and at yet other points it will practically disappear: you won't be able to hear it at all, or you hear it but greatly attenuated, very soft.

The peaks and nulls fall at different places in the room for different frequencies. So the spot in the room where one mode was deafening might turn out to be the null for a different node.

Conversely, if you have a mode (standing wave) that forms at a specific frequency, then playing at a slightly different frequency might show no mode at all: for example, if a tone of exactly 73 Hz creates a standing wave that is clearly identifiable as you walk around the room, with major nulls and peaks, then a tone of 77 Hz might show no modes at all: it sounds the same at all points in the room. Because there are no natural resonances, no "room modes" associated with that frequency.

That's the problem. A BIG problem.

Of course, you don't want that to happen in a control room, because it implies that you would hear different things at different places in the room, for any give song! At some places in the room, some bass notes would be overwhelming, while at other places the same notes would be muted. As you can imagine, if you happen to have your mix position (your ears) located at such a point in the room, you'd never be able to mix anything well, as you would not be hearing what the music REALLY sounds like: you would be hearing the way the room "colors" that sound instead. As you subconsciously compensate for the room modes while you are mixing, you could end up with a song that sounds great in that room at the mix position: the best ever! But it would sound terrible when you played it at any other location, such as in your car, on your iPhone, in your house, on the radio, at a club, in a church, etc. Your mix would not "translate".

And you also don't want major modal issues in a tracking room, for similar reasons: As an instrument plays up and down the scale, some notes will sound louder than others, and will "ring" longer. The instrument won't sound even and balanced.

OK, so now I have painted the scary-ugly "modes are terrible monsters that eat your mixes" picture. Now lets look at that a bit more in depth, to get the real picture, and understand why they look bad, but aren't so bad in reality.

So let's go back to thinking about those room modes (also called "eigenmodes" sometimes): remember I said that they occur at very specific frequencies, and they are very narrow? This implies that if you played an E on your bass guitar, it might trigger a massive modal resonance, but then you play either a D or an F and there is no mode, so they sound normal. Clearly, that's a bad situation. But what if there was a room mode at every single frequency? What if there was one mode for E, a different mode for D and yet another one for F? In that case, there would be no problem, since all notes would still sound the same! Each note would trigger its own mode, and things would be happy again. If there were modes for every single frequency on the spectrum, and they all sounded the same, then you could mix in there with no problems!

And that's exactly what happens at higher frequencies. Just not at low frequencies. Because of "wavelength"...

It works like this: remember I said that modes are related to the distance between walls? It's a very simple relationship. Remember I said the waves are "standing" because the peaks and nulls occur at the same spot in the room? In simple terms, for every frequency where a wave fits in exactly between two walls, then there will be a standing wave. And also for exactly twice that frequency, since two wavelengths of that note will now fit. And the same for three times that frequency, since three full waves will now fit in between the same walls. Etc. All the way up the scale.

So if you have a room mode at 98 Hz in your room, then you will also have modes at 196 Hz (double), 294 (triple), 392 (x4), 490(x5), 588(x6), 686(x7) etc., all the way up. If the very next mode in your room happened to be at 131 Hz, then there would also be modes at 262 Hz(x2), 393(x3), 524(x4), 655(x5), etc.

That's terrible, right? There must be thousands of modes at higher frequencies!!! That must be awful!

Actually, no. That's a GOOD thing. You WANT lots of modes, for the reasons I gave above: If you have many modes for each note on the scale, then the room sounds the same for ALL notes, which is what you want. It's good, not bad.

But now let's use a bit of math and common sense here, to see what the real problem is.

If your room has a mode at 98Hz, and the next mode is at 131 Hz, that's a difference of 32%! 98 Hz is a "G2". So you have a mode for "G2". but your very next mode is a "C3" at 131Hz. That's five notes higher on the scale: your modes completely skip over G2#, A2, A2#, and B2. No modes for them! So those four notes in the middle sound perfectly normal in your room, but the G2 and C3 are loud and long.

However, move up a couple of octaves: ...

There's a harmonic of your 98Hz mode at 588 Hz, and there's a harmonic of your 131 Hz mode at 524 Hz. 524 Hz is C5 on the musical scale, and 588 Hz is a D5. They are only two notes apart! Not five, as before.

Go up a bit more, and we have one mode at 655 and another at 686. 655 is an E5, and 686 is an F5. they are adjacent notes. Nothing in between! We have what we want: a mode for every note.

The further up you go, the closer the spacing is. In fact, as you move up the scale even higher, you find several modes for each note. Wonderful!

So at high frequencies, there is no problem: plenty of modes to go around and keep the music sounding good.

The problem is at low frequencies, where the modes are few and far between.

The reason there are few modes at low frequencies is very simple: wavelengths are very long compared to the size of the room. At 20 Hz (the lower limit of the audible spectrum, and also E0 on the organ keyboard), the wavelength is over 56 feet (17m)! So your room would have to be 56 feet long (17 meters long) in order to have a mode for 20 Hz.

Actually, I've been simplifying a bit: it turns out that what matters is not the full wave, but the half wave: the full wave has to exactly fit into the "there and back" distance between the walls, so the distance between the walls needs to be half of that: the half-wavelength. So to get a mode for 20 Hz, your room needs to be 56 / 2 = 28 feet long (8.5M) . Obviously, most home studios do not have modes at 20 Hz, because there's no way you can fit a 28 foot (eight meter) control room into most houses!

So clearly, the longest available distance defines your lowest mode. If we take a hypothetical dimensions as an example (typical of a very small home studio), and say the length of the control room is 13 feet (4m), the width is 10 feet (3m), and the height is 8 feet. (2.5M) So the lowest mode you could possibly have in that room, would be at about 43 Hz (fits into 13 feet or 4M perfectly). That's an "F1" on your bass guitar.

The next highest mode that you room could support is the one related to the next dimension of the room: In this case, that would be width, at 10 feet / 3M. That works out to 56.5 Hz. That's an "A1#" on your bass guitar. Five entire notes up the scale.

And your third major mode would be the one related to the height of the room, which is 8 feet /2.5M, and that works out to 71 Hz, or C2# on the bass guitar. Another four entire notes up the scale.

There are NO other fundamental modes in that room. So as you play every note going up the scale on your bass guitar (or keyboard), you get huge massive ringing at F, A# and C#, while all the other notes sound normal. As you play up the scale, it goes "tink.tink.tink.BOOOOM.tink.tink.tink.tink.BOOOOOM.tink.tink.tink.BOOOOOM.tink.tink...."

Not a happy picture.

There are harmonic modes of all those notes higher up the scale, sure. But in the low end, your modes are very few, and very far between.

So, what some people say is "If modes are bad, then we have to get rid of them". Wrong! What you need is MORE modes, not less. Ideally, you need a couple of modes at every single possible note on the scale, such that all notes sound the same in your room. In other words, the reverberant field would be smooth and even. Modes would be very close together, and evenly spread.

So trying to "get rid of modes" is a bad idea. And even if it were a good idea, it would still be impossible! Because modes are related to walls, the only way to get rid of modes is with a bulldozer! Knock down the walls... :shock:

That's a drastic solution, but obviously the only way to get a control room that has no modes at all, is to have no walls! Go mix in the middle of a big empty field, sitting on top of a 56 foot (17 M) ladder, and you'll have no modes to worry about.... 8) :roll:

:shot:

Since that isn't feasible, we have to learn to live with modes.

Or rather, we have to learn to live with the LACK of modes in the low end. As I said, the problem is not that we have too many modes, but rather that we don't have enough of them in the low frequencies.

Obviously, for any give room there is a point on the spectrum where there are "enough" modes. Above that point, there are several modes per note, but below it there are not.

There's a mathematical method for determining where that point is: a scientist called Schroeder figured it out, years ago, so it is now known as the Schroeder frequency for the room. Above the Schroeder frequency for a room, modes are not a problem, because there are are lots of them spaced very close together. Below the Schroeder frequency, there's a problem: the modes are spaced far apart, and unevenly. (The Schroeder frequency is a bit more complex than just that, since it also considers treatment, but this gives you an idea...)

So what can we do about that?

All we can do is to choose a "room ratio" that has the modes spaced out sort of evenly, and NOT choose a ratio where the modes are bunched up together. For example, if your room is 10 feet long and 10 feet wide and 10 feet high (3m x 3m x 3m), then all of the modes will occur at the exact same frequency: 56.5 Hz. So the resonance when you play an A1 on the bass, or cello, or hit an A1 on the keyboard, will by tripled! It will be three times louder. The nulls will be three times deeper. That's a bad situation, so don't ever choose room dimensions that are the same as each other.

You get the same problem for dimensions that are multiples of each other: a room 10 feet high (3m) by 20 feet wide (6m) by 30 feet long (9m) is also terrible. All of the second harmonics of 10 feet will line up with the 20 foot modes, and all of the third harmonics will line up with the 30 foot modes, so you get the same "multiplied" effect. Bad.

In other words, you want a room where the dimensions are mathematically different from each other, with no simple relationship to each other.

That brings up the obvious question: What ratio is best?

Answer: there isn't one! :)

Over the years, many scientists have tested many ratios, both mathematically and also in the real world, and come up with some that are really good. The ratios they found are named after them: Sepmeyer, Louden, Boner, Volkmann, etc. Then along came a guy called Bolt, who drew a graph showing all possible ratios, and he highlighted the good ones found by all the other guys, and predicted by mathematical equations, plus a few of his own: If you plot your own room ratio on that graph, and it falls inside the "Bolt area", then likely it is a good one, and if it falls outside the "Bolt area", then likely it is a bad one. Sort of.

So, there are no perfect ratios, only good ratios and bad ratios.

It is impossible to have a "perfect" ratio in a small room, simply because that would require enough modes to have one mode for every note on the musical scale, but that's the entire problem with small rooms! There just are not enough modes in the low end. So you can choose a ratio that spreads them a bit more this way or a bit more that way, but all you are doing is re-arranging deck chairs on the Titanic, in pleasant-looking patterns. The problem is not the location of the deck chairs; the problem is that your boat is sunk!: Likewise for your studio: the problem is not the locations of the modes: the problem is that your room is sunk. No matter what you do with the dimensions, you cannot put a mode at every note, unless you make the room bigger. It is physically impossible.

But that does not mean that your room will be bad. That's the common perception, and it is dead wrong.

All of this leads to the question you didn't ask yet, but are probably heading for: What can I do about it?

Here's the thing: Modes are only a problem if they "ring". The wave is only a problem if the energy builds up and up and up, with each passing cycle, until it is screaming, and then the "built up" energy carries on singing away, even after the original note stops. That's the problem. If you stop playing the A1 on your guitar, and the room keeps on playing an A1 for a couple of seconds, because it "stored" the resonant energy and is now releasing it, then that's a BIG problem! The room is playing tunes that never were in the original music! :shock:

If a mode doesn't ring like that, then it is no longer a major issue. (It is still an issue for other reasons, just not a major one....)

So how do you stop a mode? You can't stop it from being there. But you CAN stop it from "ringing". You can "damp" the resonance sufficiently that the mode dies away fast, and does not ring. You remove the resonant energy and convert it into heat: no more problem! In other words, it's not good if you own a large angry dog that barks all the time and bights your visitors, but it's fine to own a large angry dog with a muzzle on his mouth, so he cannot bark and cannot bight!

You do that with "bass trapping". A bass trap is like the dog muzzle. It doesn't get rid of the problem, but it does keep it under control. You use strategically placed acoustic treatment devices inside the room that absorb the ringing of the mode, then it cannot ring. There are several ways to do that, with different strategies, but the good news is that in most rooms it is possible to get significant damping on the modes, so that they don't ring badly, and don't cause problems. Note that bass trapping does not absorb the mode: it just absorbs the ringing. Some people don't understand this, and think that the bass trapping makes the modes go away: it doesn't. All it does is to damp them. The modes are still there, and still affect the room acoustics in other ways, but with good damping, at least they don't "ring" any more.

And that is the secret to making a control room good in the low end! Choose a good ratio to keep the modes spread around evenly, then damp the hell out of the low end, so modes cannot ring. It's that simple.

The smaller the room, the more treatment you need. And since those waves are huge (many feet long), you need huge bass trapping (many feet long/wide/high/deep). It takes up lots of space, and the best place for it is in the corners of the room, because that's where all modes terminate. If you want to find a mode in your room, go look for it in the corner: it will be there. All modes have a pressure node in two or more corners, so by treating the corners, you are guaranteed of hitting all the modes.

As I said, there is no single "best" ratio, but there are good ones. You can use a "Room Mode Calculator" to help you figure out which "good ones" are within reach of the possible area you have available, then choose the closest good one, and go with that. And stay away from the bad ones.

Arguably, Sepmeyer's first ratio is the "best", since it can have the smoothest distribution of modes... but only if the room is already within a certain size range. Other ratios might be more suitable if your room has a different set of possible dimensions. So there is no "best".

But that's not the entire story: So far, all the modes I have mentioned are only related to two walls across the room, opposite from each other. I mentioned modes that form along the length axis of the room (between the front and back wall), others that form along the width axis (between left and right walls), and others that form on the height axis (between floor and ceiling): Those are the easiest ones to understand, because they "make sense" in your head when you think about them. Those are called "axial modes", because they form along the major axes of the room: length axis, width axis, height axis.

However, there are also other modes that can form between four surfaces, instead of just two. For example, there are modes that can bounce around between all four walls, or between the front and back walls as well as the ceiling and floor: those are called "tangential modes". And there are other modes that can form between all six surfaces at once: they involve all four walls plus the ceiling and the floor. Those are called "oblique modes".

The complete set of modes in your room consists of the axial modes, plus the tangential modes, plus the oblique modes.

That's what a good room mode calculator (a.k.a. "room ratio calculator") will show you. There are bad calculators that only show you the axial modes, which is pretty pointless, and the good ones show you all three types.

Use one of these Room Ratio calculators to figure out the best dimensions for your room:

http://www.bobgolds.com/Mode/RoomModes.htm

http://amroc.andymel.eu/

Both of those are very good, and will help you to decide how best to build your room. They give you tons of information that is really useful to help figure out the best dimensions.

However, modes aren't that important, despite all the hype they get: Modes are one aspect of room design, but there are many more. It's wise to choose a ratio that is close to one of the good ones, or inside the Bolt area, but you do NOT need to go nuts about it! There's no need to nudge things around by millimeters or smalls fractions of an inch, hoping to get a "better" ratio. Just stay away from the bad ones, get close to a good one, and you are done. End of story.

----------

OK, that's the end of the "cut and paste" about modes. I hope that helps you get the idea why "Going to keep the strange pitch of the roof as I hope it will reduce room modes" is not necessary, or even good. If you want to keep the roof shape because you like it, or because your bylaws say you have to, or because you don't fell like building more brickwork to get it higher, then fine! But keeping the shape in order to try to reduce the modes, is not a good reason, if it it would work.


> Thanks for all of that, very educational. My limited understanding was that irregular shaped rooms are often better sounding. I understand what you are saying. I'd like to keep the odd shape mainly as it maximises height at the back end where the entrance will be.

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> walls: brick, single skin & pebble dash rendering on outside.
:thu: So you have a decent floor (concrete slab) and decently massive outer-leaf walls. All you need to do to complete the outer-leaf shell, is to replace your roof with something that has similar surface density, and install doors and windows that also have similar surface density.


> So, "similar surface density" means thickness in this case?

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> Doors: Two large wooden garage doors (to replace by bricking up and adding 2 door -inner & outer- system.)
:thu: Perfect!


>Great.

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> Electrics: Double wall socket and light installed. New Board to go in (Awaiting quotes) Thinking of mostly surface mounted power and lights.
:thu:

There's one item you missed from your list, and it's a biggie! HVAC. Yes, you absolute do need that. No, it is not a luxury. It is just as necessary as having speakers in a control room, or mics in the live room. Without a proper HVAC system, you don't have a usable studio.


> Yep, I mentioned it later down I think. Deffo on my list. As you say further down, I will ensure the system is capable of a full room of people, not just myself. Makes sense.

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> New roof needs to be installed. Should the rafters be cut into the walls? or is it ok to mount to the walls as some of the existing smaller beams have been in the pics? (I doubt it)
Your structural engineer will guide you there (yes, you need one of those too!) Depending on what type of roof you install, that will pretty much dictate how it is to be built. The most important point about your new roof is that it MUST have the same surface density a your walls. So you will need to use something very massive (heavy) that has roughly the same surface density as brick. I would suggest "beam and block" as a good possibility. Another option would be just to pour a concrete roof. A distant third would be to build it up from trusses and a very massive deck (multiple layers of OSB / plywood / fiber-cement board) with asphalt shingles as the final surface. But talk to your builder-friend, and also to your structural engineer, to see what that suggest. Listen to, and obey, your structural engineer! He is the ONLY person who is qualified to guide you on this! And since he will be the one signing the paperwork for your permit and inspection applications, it's on his head to get it right. If he doesn't get it right, then the roof will be on YOUR head! Literally.... :)


> Thanks. I don't have a structural engineer. I was going on the builders recommendations. You see, I don't need planning permission for this in the UK. As I am not changing the roof height, it is what's know as a "Change of use" build. I just purchase a certificate, submit a drawing of the change of use design, and pay for the building regs check and I can start work. But, you've got me thinking that I should maybe get a structural engineer. You see I was just going to do the best I could on the roof and go with the builders suggestion. I'll look into the beam and block, thank you. That seems a bit excessive but as you say, it needs to be dense.

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Should I use deeper rafters? I’m thinking I’ll use the 2 existing rafters that have been cut into the brick but add new additional beams to support the new roof.
Once again your structural engineer is the only guy qualified to tell you that. You can look up things on span tables, and calculate masses and deflections and densities and things your self, for sure, but you will ALWAYS need a certified local structural engineer to confirm that your calculations are correct, and he will put his signature on the paperwork that you present in order to get your building permits, and your inspections.


> As above.

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How many layers of ply for the new roof would you suggest? I was thinking 3.
See above. But don't guess! Do the math yourself: The absolute density of brick is about 2300 kg/m3. The absolute density of plywood is around 560 kg/m3, so call that about a quarter of the density of brick. So if your bricks are "standard" 102mm thick, then the surface density of those is about 230 kg/m2, roughly. To get the same surface density with plywood, it would have to be four times as thick (because plywood is one fourth the density), so that would be 400mm thick. Plywood usually comes in sheets that are 16mm, 19mm, or 25mm thick. Assuming you can get 25mm, you would need 400/25 = 16 layers. Not three layers, but sixteen layers. That would get you to the same surface density as that of your walls... :shock:


> Yep. Going to research. see next answer.

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I'm sure you were not expecting that! But that's the sad truth. Assuming you want good isolation for your studio, the outer-leaf shell needs to have the same surface density all around. The entire "envelope" must have the same weight per square meter. Your isolation is only as good as the weakest part. So if you have great walls, a great floor, and great windows and doors, but a lousy roof, then the roof is the "weakest link". It sets the limit for your total isolation.


> I see lots of UK garage builds that just use an OSB roof and the results are good, that is what I based my plan on.I get what you are saying though.

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OK, so clearly is is unrealistic to do this with plywood, assuming that you want decent isolation. Hence my suggestion of "beam and block" for your roof. Look into it.


> Will do.

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Now, so far I'm assuming that you have already figure out how much isolation you need, in terms of decibels. If you don't yet know that, then that's the very first things you need to do: buy a hand-held sound level meter (around US$ 100 for a decent one), and measure. The number you come up with here is what defines the entire construction of your studio! It is a VERY important number. So measure with care, think it through carefully, then decide on that number realistically.


> I already have a meter. I'm not sure what you recommend I measure though? Are you suggesting I play drums in there and measure outside? I don't even have a drum kit LOL. Also the garage is full of crap at the mo. Please clarify. How do I ascertain how much isolation I need if I don't know how loud it will be. As I say, I'll be making less noise than guys having full bands playing.

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OK, so let's say that you figure out you actually don't need so much isolation, an you can live with a very weak link up above you, built from 75mm of plywood ( three layers of 25mm). You COULD do that, yes, as long as you do the math to determine what ELSE you wold need to do, to get the isolation you need. You already know that you need an inner-leaf, in addition to the outer leaf, so there are ways of compensating for deficiencies in the outer leaf, by doing things differently in the inner-leaf. Yes. It can be done. But you need to do the math here: you need to use the equations for 2-leaf structures to figure out how to build your outer-leaf roof and inner-leaf ceiling such that together, AS A SYSTEM, they provide the isolation you need.


> I really do want to attempt to do this properly but how do I "Do the math"? I don't know what to measure; as above. I'm not sure how to evaluate the isolation "AS A SYSTEM" either. :(

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Is it worth putting some sort of Tecsound membrane in-between one of the layers?
Yes. No. Maybe. Certainly. Absolutely not. Could be.... :) Sorry to be cryptic, but there's no way of answering that without first knowing how much isolation you need, and how you plan to get it. Your calculations will tell you how much MASS you need up there on the roof, but it won't tell you what brands and models of building materials to use. In fact, sound waves don't care at all! They are not snobbish, they can't read the price tags on your building materials, and they just don't care how much you paid for it. All they respond to is the mass of each leaf, and the air spring between them, and the damping inside. They don't care at all if you paid handsome prices for the mass and damping, or if you got it from the bargain shelves. So it's best to go with the least expensive materials that will do the job.


> OK. Understood. As above too.

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Using the clip system, I plan to attach the rock wool into the roof cavities between beams, then resilient bar off the rafters connecting to the clips and drywall.
Ummmm.... this might seem a little harsh, but how on earth did you arrive at that solution, when you don't even know how much isolation you need? You are just guessing and hoping. Guessing and hoping is not a good way to build a studio. Instead, do the math. It's not that hard. It would be really sad if you invest all this money, and time, and effort, only to find that the room is no use because it doesn't isolate properly...


> I'm guessing as I have no idea how much isolation I will need (as above). I appreciate that this may seem strange to you that I don't know this, but I suppose my thinking from the outset was based on doing the best I thought possible in regards to isolation, and hoping it would be enough. Writing that makes me realise that this is not the best method. It's just that I have to get this done THIS YEAR and want to crack on ;) It was also based on space. The clip system would maximise height as the inner skin clips onto the roof rafters. This is the system: https://www.soundproofingstore.co.uk/so ... fing-guide (scroll down to Timber ceiling) - have also attached a image to the images


> As I’m trying to maximise space, I got some quotes for a Isomax/Genie clip system. £3k for all walls and ceiling. I don’t think I can afford that much on the entire system, so I was thinking of just putting the clip system on the ceiling as that is really the dimension that needs maximising (2.4m high at lowest end). If I build a standard inner leaf (timber frame >rock wool >Plasterboard green glue> plasterboard) it will be cheaper and I don’t mind losing the space, I’ll probably get better isolation too. I’m assuming that it will be fine to combine 2 methods? i.e. decoupling system on the ceiling to maximise height and the walls to be standard Frame/Drywall Green glue. The walls and ceiling won’t actually touch.[/quote]Once again, you are basing your decisions on the wrong factors! As soon as you see yourself writing "I think..." and "I was thinking..." and "I'm assuming...." and "probably....", that should be raising major red flags! Never, ever base any part of your room design on guesses, assumptions, "think"'s or "probably"'s. Instead, do the math to be CERTAIN that you will get what you are needing.

> Clip system attached to the roof beams, the walls would be to the floor. That is what I was asking, can these two systems be combined. Also not sure what "math to do" as above. So you see, I based my plan on space maximisation too. Hence the clip system on the roof and a inner leaf consisting of 4 walls. Hope that makes sense. I appreciate that I need to calculate too, just not sure how :)

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I assume that I don’t actually need to build a timber frame against the existing brick walls (Outer leaf) but simply need to work out what I can use to hold the rock wool against this outer skin. Anyone have any suggestions?
Put up your inner-leaf framing, then fill the entire cavity with the correct insinuation, then put the vapor barrier on (if applicable), then put the drywall (plasterboard) on. It's that simple. The vapor barrier (assuming that your building codes says that you need it) and the drywall will hold the insulation in place. Use semi-rigid batts to help ensure that everything stays nice and vertical, without slumping down.


> Yep I get that, but I was also going to put rockwool on outer skin so that there is is insulation on the inside of both leafs, as I have seen in Rod's book and in your leaf images. I assume it is a waste of money just to build a frame against the outer skin (brick wall) to hold up the insulation so was asking how I would hold it against this outer leaf. Are you suggesting I only use one layer of rock wool on the inner leaf and leave the brick walls bare?

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it appears that my concrete floor is fine.
:thu:


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I was thinking of adding some sort of rubber membrane and then laminate flooring on top. Any thoughts?
Use whatever underlay the laminate flooring manufacturer recommends! First choose the laminate that you want, then check the installation instructions. It will tell you how flat the slab must be (you might need to level it), and it will tell you exactly what types of underlay are approved for that specific flooring. Use the best one on the list. Don't skimp!


> Thanks!

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> I believe my best option on a budget for doors is to get 2 internal, heavy duty fire doors for the inner and outer door and use strip seals on the edges.
You are on a very tight budget: don't by the doors... build them yourself. It's not that hard. And yes, you do need seals around the complete perimeter of each door: top, both sides, and the bottom. You need at least two such seals on each door, and three is better. For the threshold, drop-down door seals are very recommended. You will also need heavy duty hinges (not the normal flimsy ones used on typical house doors), and you will need more of them than you think: at least four per door (rather then the usual three), and maybe as many as six, if your doors are very heavy. You will also need automatic door closers, since the doors will be too heavy to close by hand, safely. Those also need to be the right type for the weight of the door.


> Cool. Will investigate!

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> There is an existing window and Building regs say that I have to retain a window that can be opened in an emergency, so I have to keep the window. I’m struggling to find suitable new windows
It's a pity that it has to be operable, as that reduces isolation. Oh well: if that's what the regulations say, then that's what you have to do! So you will need two windows, one for the outer leaf, one for the inner leaf, and each of them will have a single pane of thick laminated glass. Get units with heavy-duct hinges, multiple seals, and a good handle that locks down well, with the correct pressure on the seals.


> Cool. Will investigate! So, for the frames, just regular UPVC windows?

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I suppose I’m just going to go with a standard triple glazed UPVC window on the outside and same on the inside.
So you don't want good isolation in the low end of the spectrum, where drums and bass guitars and keyboards live? :) Did you read the section in Rod's book on why triple-leaf is a really bad idea? Have you seen this diagram before?
Attachment:
2-leaf-3-leaf-4-leaf-STC-diagram--classic2-GOOD!!!.gif

That shows walls, not windows, but the same principle applies. Notice how a 2-leaf system is great for isolation, a 3-leaf system is worse, and a 4-leaf system is worse still. If you extrapolate, a 5-leaf system would be yet worse, and a 6-leaf would be REALLY lousy. You are proposing to put in a 6-leaf system... :shock: Two units, each with a triple-pane, makes for a total of 6 leaves...


> Good point. understood. I will not be wanting 6 leaves! lol

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I’m investigating a thin line window with thick glazing on the inside. Any suggestions?
Just put in two ordinary windows, one for the inner leaf, one for the outer, each with a single pane of laminated glass of the correct density such that it matches the density of the leaf that it is in.


> Will advise I find anything.

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> Still investigating this. I’m planning on getting a small electric heater on the wall. For ventilation I’ll more than likely be fitting the standard type of ventilation. I’m wondering, in regard to A/C can I get away with a smaller unit as I’ll be the only one in the room (most of the time) ?
Electric heaters do not dehumidify, and they do not cool, and they are very inefficient. They use a lot of electrical power, for very little actual heat. A small mini-split system is far, far more efficient (at least 300% more efficient, perhaps 400%, or more, depending on which one you buy), plus it also controls the humidity, and it also cools.

You can never get away with a unit that is smaller than you need, and you can never get away with one that is larger, either! Here too you need to do the math to figure out what size you NEED for your room. You need a certain cooling capacity, that is determined by your latent heat load and your sensible heat load, and you need a certain air flow rate, which is determined by the air volume in the room. When you do the math, you will come up with two answers: one tells you how many BTU/hr of heating/cooling capacity you need, and the other tells you how many CFM (Cubic Feet per Minute) of air you need to move. You do the calculations for the WORST CASE: a hot, humid day when all of your buddies are in there, jamming and sweating and having a great time, eating pizza, drinking beer, with a bunch of hear and effects boxes and computers and amps and lights and stuff. Then you choose a mini-split unit that just has the capacity to deal with that, when running on the very highest setting. You will mostly use a much lower setting, of course, when you are on your own, but the system has to be capable of handling the "worst-case" scenario.


> Understood. I will investigate and calculate. As I mentioned though, it will only ever be me and possibly a buddy in there at one time. Maybe 3 humans in there on the odd occasion, but yes, I will make sure the system is capable of above and beyond.

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You then also dimension your ducts and silencer boxes in accordance with those same numbers, to ensure that you are supplying enough fresh air to keep everyone alive inside the room, as well as keeping them comfortable, while also blocking enough sound so that you maintain the level of isolation that you need.


> Super!

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I read that it is better to connect the stud frame to the concrete floor and the ceiling.
You read wrong! Yes, you certainly do attach the framing to the floor, but NEVER to the ceiling. That would create a direct flanking path between the inner-leaf walls and the outer-leaf roof. In other words, it would trash your isolation.


> This idea was, as mentioned earlier, a result of planning the inner leaf roof to be fitted to the ceiling and not the inner leaf walls (hope that makes sense) a slightly different set-up than the norm. In this situation, the walls would have to be fitted to the ceiling rafters. Not saying I am going to defo do this but it was a option. Obviously, room within a room would provide more isolation.


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surely the inner leaf is now connected to the walls?
Exactly. Very correct.


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I can’t see any other way though. Maybe as it is a 2nd-hand connection the vibration transference is reduced though
Nope! There is no connection at all. The walls sit on the floor, and the ceiling sits on the wall, and NONE of that touches the existing walls or roof. End of story.


> But is would in the system I mentioned above. What are your thoughts on that?

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And, if 2 walls are decoupled from each other and only touching via sealant,
Why to you want to decouple your inner-leaf walls from each other? They are all part of the same system, so why would you want to do that?


>This question should make sense to you now? ;)

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what happens when you fit timber bass traps to both walls in a corner, is that not just connecting the walls together?
Yup! And so what? :)


> Again this is would happen using the clip system. That's why I was asking. (https://www.soundproofingstore.co.uk/so ... fing-guide)

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Green glue has the support of many and I assume this is good stuff.
It also has a proven track record, and abundant test data from independent laboratories that show HOW it works and THAT it works, exactly as advertised. Never use an acoustic product that is not backed up by independent test data.

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But how does this “Tecsound” LINK perform in comparison?
Your link doesn't work...


> Tecsound: https://www.ikoustic.co.uk/products/wal ... MnEALw_wcB

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If it is a huge difference to GG I will consider, but I’m just wondering if anyone has real world experience with both?
I can't help you there. I only use and recommend materials and products that are backed up by real data. So I have never used the product you mentioned, and never recommended it for my customers. Those of my customers that have used Green Glue compound in their walls and ceilings, have never been disappointed with the results.

But there's another question here: Why do you think you will need Green Glue compound? :)


> Because it reduces sound waves through the layers of plasterboard, and, afaik, converts the sound waves into heat, thereby reducing the sound reaching the outside world. I have heard this is a good thing! ;)

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the first 5 images are taken from the sketch up model I have created to base my plan on
Use the "perspective" view, not the "parallel" view, to show the place more realistically.

> I'll add the pics as you suggest. thanks.

Summary: Your place has decent possibilities. It is small, yes, but feasible. But you need to plan it properly, and design it properly, starting out by measuring the sound levels, and deciding on how much isolation you need, in decibels. You cannot successfully design the isolation system for a studio if you do not yet know hoe much isolation you need. Once you have that number, then you can stat using the equations and doing the math to figure out what building materials you will need in order to get the isolation that you have defined. Once you have THAT in place, you can start designing the actual method and techniques for your two-leaf system. And once that part of the design is finished, you can move on to the HVAC and electrical design, then finally the acoustic treatment design for the room interior.


> Great summary! That is exactly what I want to do. hopefully you can answer my n00b questions and I can start to make the required calculations. :)

Thanks again Stuart, I appreciate all your words of wisdom!

Sam.


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PostPosted: Thu Oct 04, 2018 1:53 am 
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Location: Santiago, Chile
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Sorry it's taken a while to respond,
No problem! Sometimes it can take me days, or even weeks, to respond to a thread... You got lucky both times, as I was on a break when I saw your posts! But it might not always be like this... :)

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I just meant that the levels will not reach that of a full band playing in there for example
Surprisingly, the level of the drums pretty much IS the level of the full band! Sounds strange, but a lot of things about acoustics are not intuitive. Let's say, for argument's sake, that your drums are coming in at 115 dBC. Then you add the rest of the band: for argument's sake, lets say that the "rest of the band" consists of bass, electric guitar, keyboards, amplified acoustic guitar, percussion, amplified vocals, sax, trombone.... You measure all the "rest of the band" by itself, playing loud, but without the drums, and you find that the level of the "rest of the band" happens to be 110 dBC. So you figure that 115 dBC from the drums plus 110 dBC from the "rest" must make a hell of a lot, right? Well, actually, no. The answer is: 110 + 115 = 116.19 dBC, to be exact. Yup. When you add one hundred and fifteen dB to on hundred and ten dB, the total is one hundred and sixteen dB. Surprising, but true. Summing sound intensities from incoherent sound sources doesn't increase the total much beyond the loudest source. "Incoherent" here simple means that the are not putting out the exact same sound. Even if they were coherent sound sources, the total would still not rise that much: Say you have two identical bass setups, and each one of them puts out 112 dBC by itself, and somehow you manage to play the exact same note on both at once such that the vibrations of the strings are exactly synchronized: in this case, 112 dBC + 112 dBC = 118.02 dBC. Not even twice as loud!

This is surprising to many people, but the simple reason is that the decibel scale is logarithmic, not linear, which is exactly the same as how our ears work anyway. Summing decibels is not just adding the numbers: you have to add the anti-log of the numbers, or use log math to add them. In simple terms, doubling the absolute sound intensity is an increase of 6 dB. In order to SOUND like it is twice as loud, subjectively, it needs to increase by TEN dB, which implies ten times the sound intensity. So if you have one bass guitar setup and you wanted a level that sounds TWICE as loud, then you would need to setup ten identical kits, and play the all in sync...

Here's the actual equation, if you are interested:

Adding two incoherent decibel levels:

Lt = L1 + 10 * log(10^^ ( (L2 - L1) / 10 ) +1)

Where L1 and L2 are the two levels, in decibels.


In other words, your basic assumption that your drum kit by itself is a lot quieter than the entire band, is not true.

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Also, if live drums are too loud in the end, I'll simply use electronic kit to trigger samples. As you can see, I am winging it a bit because I have no idea how much isolation I need for drums as I have no drums and cannot measure them in the garage as is
You don't need to measure them in your garage! You just need to measure the level. I'm sure you have access to drums SOMEWHERE, so take along your meter next time you go to play, and get someone else to hold it about a meter away from the kit while you play. In other words, just a few cm above your head: that's about a meter away. Use "C" weighting an "Slow" response for the measurement.

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My limited understanding was that irregular shaped rooms are often better sounding.
The reason irregular shaped rooms can sound better is flutter echo, not room modes. Flutter echo is another acoustic issue that forms between parallel walls, not related to room modes. It is easy to treat, flutter echo, since it generally occurs at much higher frequencies than modal issues.

The problem with non-rectangular rooms is that it is much, much harder to predict the acoustic response! There are some very simple equations that hold true for simple rectangular rooms with 6 "sides" (four walls, plus ceiling and floor = 6), where all of those are mutually parallel and perpendicular. As soon as you add another surface (for example, an eight-sided room with six walls + floor and ceiling), or angle one of more of the surfaces with respect to the others, then you can throw those simple equations out the window, and you now need very, very much more complex methods for predicting room behavior. It's a bit more complicate than that, because angling just one surface only invalidates the equations that involve that surface, but the equations for the other surfaces are still valid... so it's complex. But if you can just stick to a basic rectangle, then it's a lot easier.

That said, if the room is small, then it is usually better to do whatever you can to increase the interior volume of the room as much as possible, provided that you don not lose the LEFT/RIGHT SYMMETRY of the room: Raising the roof at one end is a good possibility, since it increases the volume without affecting symmetry. However, it does also complicate the issue with reflections....

There's nothing simple about studio design: anything you do to the room will alyways have multiple consequences in various places that you never even suspected!

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I'd like to keep the odd shape mainly as it maximises height at the back end where the entrance will be.
That's fine! More height at the back is a GOOD thing. More height at the front: not so good.

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> So, "similar surface density" means thickness in this case?
Not necessarily! "surface density" means "how much does each square meter weigh". In other words, if you could take a large saw to the wall, floor, ceiling, window, door, or whatever, and cut out a piece that measures one meter on each side, how heavy would that be? It's not just the thickness: it's the materials. In more technical terms, it is the absolute density of the material, mutilated by the thickness. So, a one square meter piece of concrete 10mm thick will weigh about 24 kg, but the same size piece of plywood 10mm thick will weigh only 5.6 kg, the same size piece of plasterboard will weigh 6.8 kg, while the same size piece of MDF will weigh 7.5 kg, and the same size piece of fiber-cement board will weigh 15.5 kg, and if you really want to go to extremes, the same size piece of steel plate will weight 78 kg, and the same size piece of lead sheet will weigh 125 kg. At the other extreme, the same size piece of cardboard will weigh just 0.5 kg. Those are the surface densities of those materials, for a one square meter area that is 10mm thick.

The basic concept of isolation is that each complete leaf must have the same surface density all around. So in places where you can use materials that are high density, they can be thinner and still have the same surface density, but in areas where you used materials with lower density, you have to make them thicker to get the same surface density.

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Thanks. I don't have a structural engineer.
You'll need one! I'm aware of the "permitted development" regulations in the UK, as I have designed several studios for customers there who wanted to stay within those regs. Yes, I know the rules are pretty hazy about presenting structural calculations for that, from a legal standpoint, but you still do need this. Don't ignore page 4!

Attachment:
permitted-development-UK-extract.jpg

"... does not remove requirements for ..." Take a close look at that.

You will likely also find that if you modify a building that was previously covered by your home-owners' insurance policy, it no longer will be covered if your modifications do not meed normal building code standards, regardless of what Permitted Development allows. So if you build your place perfectly fine under Permitted Development, with all the right signatures and stamps on it, but then the roof collapses on your band and kills the lead singer, well, that's your responsibility, both civilly and criminally....

On the other hand, if a qualified structural engineer signed off on that roof, things are different... Firstly, of he is competent, it's not going to collapse, and second, even if it does, the responsibility is now mostly his, and only partly yours...

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I was going on the builders recommendations.
Yup! And if the roof collapses based on his recommendations, it's still on you, not him! You are the home owner, you are one doing the modifications, you signed the paperwork... Unless you can convince him to give you his guarantee in writing that the roof is sound and solid, it's all on you...

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> I see lots of UK garage builds that just use an OSB roof and the results are good,
Have you checked that those other "garage builds" you saw have the same isolation needs as yours? Did you check that the results are both legal and also acceptable to the neighbors? :)

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> I already have a meter. I'm not sure what you recommend I measure though? Are you suggesting I play drums in there and measure outside? ... Please clarify. How do I ascertain how much isolation I need if I don't know how loud it will be.
Set your meter to "C" and "Slow". Set up a full-range speaker inside the garage the way it is right now, and play typical commercial rock music (lots of drums and bass) at a level of about 110 dBC inside the garage (wear ear protection!), close the doors and windows, then walk around outside measuring in several places, and taking careful notes. Particularly measure at your property line, both to the street and also at the closes points to your neighbors. Then turn off the music, and go back to those exact points at the quietest time of day (probably late at night), and measure the background ambient level at each point. For each point, subtract the "quiet" from the "loud", and that's how much isolation you need to get your music down to ambient level at that point. Find the largest isolation number on your list: that's how much EXTRA isolation you need IN ADDITION to what the garage is already providing, as it is right now. But also compare the "quiet" numbers with the legal limit for how loud you can be: if the legal limit is lower than the ambient levels, then use the legal limit for your "quiet" levels.

I'm using 110 dBC as the reference level here, since that's a reasonable estimate for how loud a typical garage band would be, when playing quietly. It might be heading up to 120 if they decide to go a bit crazy. If you then decide that you won't ever record any live instruments, and just want to track electronic instruments and mix on speakers, then use a level of about 95 dB for the tests. Most engineer mix at around 75 - 85 dBC, but they always "turn it up to check the bass" every now and then, and that usually goes about twice as loud, so call it 95 dBC.
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> I really do want to attempt to do this properly but how do I "Do the math"? I don't know what to measure; as above. I'm not sure how to evaluate the isolation "AS A SYSTEM" either
Your isolation system is two-leaves. You have an outer leaf, and an inner leaf. They work together NOT individually! This is one of those cases where "the whole is greater than the sum of it's parts". Each leaf by itself does something, but when the operate together, as a single resonant system, the total isolation is very different.

So, you first need to figure out the surface density of each of your leaves, based on the materials and thickness, as I showed above. Then you need to plug those numbers into the following method. The equations for calculating total isolation of a two-leaf wall are simple:

First, for a single-leaf barrier you need the Mass Law equation:

TL = 14.5 log (M * 0.205) + 23 dB

Where: M = Surface density in kg/m2

For a two-leaf wall, you need to calculate the above for EACH leaf separately (call the results "R1" and "R2").

Then you need to know the resonant frequency of the system, using the MSM resonance equation:

f0 = C [ (m1 + m2) / (m1 x m2 x d)]^0.5

Where:
C=constant (60 if the cavity is empty, 43 if you fill it with suitable insulation)
m1=mass of first leaf (kg/m^2)
m2 mass of second leaf (kg/m^2)
d=depth of cavity (m)

Then you use the following three equations to determine the isolation that your wall will provide for each of the three frequency ranges:

R = 20log(f (m1 + m2)) - 47 ...[for the region where f < f0]
R = R1 + R2 + 20log(f x d) - 29 ...[for the region where f0 < f < f1]
R = R1 + R2 + 6 ...[for the region where f > f1]

Where:
f0 is the resonant frequency from the MSM resonant equation,
f1 is 55/d Hz
R1 and R2 are the transmission loss numbers you calculated first, using the mass law equation

And that's it! Nothing complex. Any high school student can do that. It's just simple addition, subtraction, multiplication, division, square roots, and logarithms.

You now have three numbers which tell you how much isolation you will be getting at the resonant frequency of the wall system, the coincidence dip, and the region in between. That gives you a good idea of the total isolation you'll be getting.

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> I'm guessing as I have no idea how much isolation I will need (as above).
That's why you need to figure it out! This is the number on which your entire design is based.

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I suppose my thinking from the outset was based on doing the best I thought possible in regards to isolation, and hoping it would be enough. Writing that makes me realise that this is not the best method.
Yup! You are going to spend a lot of time, money, and effort on doing this. "guessing" and "hoping" is not a good way to get the outcome you want...

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It's just that I have to get this done THIS YEAR
Ummmm.... don't look now, but we are already in OCTOBER! That gives you less than three months... Not gonna happen. Sorry. At least, not if you want to do it properly. I don't want to rain on your parade, but this is just not realistic to think you can design and build a studio inside a garage in three months. The very fastest that I have ever managed to complete a garage conversion is 2 months, from the day the customer first contact me until the day he opened the doors and his first client walked in for the first session. It was incredibly hectic, I was dedicated 100% to the design process while he was demolishing things and building things in parallel. He had a team of seven experienced builders, working 12 hour days, and me doing the design. Every day I fed them a bit more of the design, so they would have something to keep them busy that day, while I moved on to the next part. Two months, nine people, full time, good budget.

That's the very best case: most projects take six months to a year, sometimes far more.

Sorry, but it is not realistic to expect that you can do this in three months. If you start now, you MIGHT be able to get the design completed by December 31, with a lot of luck, and a lot of research, and a lot of hard work. Then allow at least another 3 to six months for the actual build.

Take a look at the corner control room thread, to get an idea of what it takes: viewtopic.php?f=2&t=21368


Quote:
The clip system would maximise height as the inner skin clips onto the roof rafters.
Actually, that's not the highest you can get your ceiling! :) An "inside-out" ceiling can beat that... "Impossible!" you say... but there are several things you are not considering, such as the difference between the ACOUSTIC ceiling height and the VISUAL ceiling height, AFTER the treatment is installed....

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This is the system:
That's just one of many similar resilient mounting systems. And they all suffer from the same drawback: there is a limit on how much isolation they can produce, which is about 16 dB higher than the same construction done WITHOUT the resilient mounts. The reason is simple: With a true fully decoupled two-leaf system, the only connection between the inner leaf and outer leaf, is air. The air acts as a very "soft" spring. When you put a resilient mount in there, you now have TWO connections going on: the air is still there, but IN PARALLEL with that, you now have the resilient mount, which is also a spring, but it is a very much HARDER spring than air. And since it is in parallel with the air, it REDUCES the total isolation that can be achieved by the air alone.

So, if you want to limit your isolation, then use clips! That might be fine if you do not have high isolation needs, but you won't know that until you do the tests with your meter, and figure it out... :) Once you know how much isolation you NEED, then you can look at te various options for getting that much isolation and choose the one that best fits your budget. Did I mention that resilient mounts are expensive, while air is free? :)

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> Clip system attached to the roof beams, the walls would be to the floor.
If your ceiling is not firmly attached to your walls, then how will you brace the tops of the walls so they don't wobble around? :shock:

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So you see, I based my plan on space maximisation too. Hence the clip system on the roof and a inner leaf consisting of 4 walls.
It's not space that you need to maximize, but rather volume. You need as much are volume inside the room as you can get. The best way to achieve that is with "inside-out" wall and ceiling construction. Greatest volume for highest isolation in smallest thickness, including acoustic treatment.

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> Yep I get that, but I was also going to put rockwool on outer skin so that there is is insulation on the inside of both leafs,
I think you missed the part where I said you fill the ENTIRE cavity between the two leaves, not just the stud bays. In other words, if you use 40x90mm studs, and decide to have a 20mm gap between the stud frame and the existing brick outer-leaf, then you fill the entire (90+20=) 110 mm air space, NOT just the 90mm stud bays. If you leave empty air in your wall cavity, then you are not maximizing isolation. The insulation acts as a damper on the various resonances that are going on inside your wall cavity, and it also slows down the speed of sound, and changes the way air deals with heat from adiabatic to isothermal, as well as doing other good things. If you only fill part of the cavity, then you only get those "good things" in part of the cavity! If you fill the cavity completely, then you get as much of the "good things" as possible.

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I assume it is a waste of money just to build a frame against the outer skin (brick wall) to hold up the insulation
Yes, absolutely!

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so was asking how I would hold it against this outer leaf. Are you suggesting I only use one layer of rock wool on the inner leaf and leave the brick walls bare?
I'm suggesting that if your total air cavity is 110mm then you fill it with semi-rigid batts totally 110mm thick, or if the cavity is 140mm then you fil it with semi-rigid batts totaling 140mm thick. Semi-rigid insulation bats will stay in place just fine, as long as the gap isn't too deep. If it is very deep, then use impaling clips on the brick, and press the batts onto those.

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> This idea was, as mentioned earlier, a result of planning the inner leaf roof to be fitted to the ceiling and not the inner leaf walls (hope that makes sense) a slightly different set-up than the norm. In this situation, the walls would have to be fitted to the ceiling rafters.
Assuming you do that, how would you decouple the inner-leaf ceiling from the inner-leaf walls? And how would you brace the wall tops to get the structural rigidity that you need, so they don't flop around all by themselves? :) I know the answer, but I'll let you do some research to convince yourself that it's not a good solution...

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> But is would in the system I mentioned above. What are your thoughts on that?
If you can show me how you would brace your walls so that they are structurally sound WITHOUG having any ceiling framing resting on top of them, and also show how you would decouple the ceiling from the walls, and also show the math proving that this system will produce the level of isolation that you need, then I'd say: "Go for it!". It is POSSIBLE, yes, but the cost is rather extravagant, and I'm pretty sure you said you are on a tight budget... :) Personally, I prefer to go with the least expensive option that will do the job, and the one that provides the most interior room volume at the same time, as well as ALSO proving the largest interior visually, AFTER the acoustic treatment is in place. Don't confuse the final visual interior with the actual physical acoustic boundaries of the room. They don't have to be the same...

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Quote:
Your link doesn't work...

> Tecsound: https://www.ikoustic.co.uk/products/wal ... MnEALw_wcB

Take a look at their own data, and tell me if there's a good improvement or not:
Attachment:
Tecsound-SY70-data.jpg

That's from their own (rather poor, very incomplete) technical data. To start with, it only shows isolation above 100 Hz, so it entirely skips the bottom two octaves of the musical scale ( :roll: ) which is the most important: your drums and bass, and the low end of the electric guitar, all live below 100 Hz. IT then shows mediocre improvement above that: at 500 Hz, the untreated floor gets about 60.7 dB, the treated floor gets 62.0. Barely 1 dB change. At 1 kHz (the "standard" level): Untreated = 66.1 dB, treated = 69.8. A bit more than 3 dB change. Barely noticeable. (you need a change of 3 dB before it is noticeable to most people). At 2 kHz, you get 64.7 dB untreated, 70.3 dB treated. Nearly 6 dB, which is more interesting, but still nothing to write home about! The very best improvement is at 200 Hz, where untreated is 45.6 dB and treated is 45.6 dB so 9 dB change. That's significant. The total change across the small potion of the spectrum that they measured, is 6 dB (improves from 59 to 65). Interesting, but not fantastic, and most of the improvement is in the mid range.

However, do note that they started with pretty good isolation already, in the untreated system! IT was already getting 59 dB of isolation... And do notice that in both cases, the system is NOT decoupled! Hence, it wil be lousy in the ow end... which the conveniently did not measure...

So, does it work? Clearly, yes it does. Not fantastic, but there's a usable effect. On the other hand, you could have gotten better results, cheaper, by simply adding another layer of drywall...

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> Because it reduces sound waves through the layers of plasterboard, and, afaik, converts the sound waves into heat, thereby reducing the sound reaching the outside world. I have heard this is a good thing!
Well, yeah, but GG doesn't just "reduces sound waves through the layers of plasterboard". It does rather more than that. It is a highly visco-elastic constrained layer damping compound, that works mostly on the BENDING waves that travel ALONG the wall, not through the wall. When the wall surface flexes in and out due to the pressure waves "sucking" and "pushing" at it, those bending waves are not really going "through" the wall (not directly, anyway). rather, they are going along the surface of the wall, like ripples on the surface of a pond (sort of!). As it does that, the GG between the two layers of drywall "damps" that action, absorbing some of the energy. It does something similar at higher frequencies, around the coincidence dip.

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hopefully you can answer my n00b questions and I can start to make the required calculations.
:thu: See above.... But you are only just getting started with calculations... there's a lot more in your future! :)



- Stuart -


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