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PostPosted: Sun Feb 18, 2018 2:57 am 
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Location: London, UK
Hello all,

Been a member here for a few years and been constantly fascinated by the depth of experience and knowledge that’s kicking around. I’d like to ask a couple of very quick, basic questions about a small project I’m about embark upon.

Here in London I have a small (4m x 3m) brick built outhouse that I want to convert into a basic studio to house a DAW and a small vocal/overdub booth. It has a pretty sturdy concrete base that has been tiled over with ceramic tiles. I’m thinking I will leave the floor well alone as the concrete should do enough of a job of dampening the kind of SPLs that I’m likely to be creating. (Will probably carpet or put a laminate down when finished) However, I’m looking at building a new skin inside the main structure comprising 4”x2” stud, rockwool in the cavity and probably 2 layers of 12mm plasterboard/gypsum. Electrics and lighting will all be surface mounted. There are a couple of things that are bugging me though and I’d be really grateful for a little feedback -

Budget - £2,000-ish (Materials only. I’ll be doing the work myself)

Although I haven’t started pulling it apart yet, the existing ceiling seems to be thin ply nailed directly to the underside of the (felt) roof rafters. Am I correct in thinking that in order to avoid the dreaded 3 leaf effect it would be best to pull this old ceiling down and run additional rafters from my new stud walls, infill with rockwool and attach a couple of new layers of plasterboard to that? If possible, I would be looking at running the new ceiling rafters parrallel with and to drop a couple of inches below the existing ones in order to preserve the (minimal) ceiling height. Does this seem about right or am I missing something?

The other bit was, is it worth running the floor plate for the new walls on neoprene? The thing with this is that I have no idea how to work out the “squash” factor here. I guess I would somehow have to figure out the total weight that the walls and celing would have to support and then find out what spec of rubber would be most adequate for it.

Of course, in amongst all this is the fact that the noise levels that are likely to be created are not those of the full on “band in a room” variety. Just usual monitoring levels, with the very occasional blast of something a little louder, so maybe I’m over-considering what to do here anyway. I dunno.

There will also be a very small vocal/iso booth (same construction) which I’m not sure whether or not to try to decouple from the existing floor. My thinking is that I probably should, but wouldn’t that then mean a floating floor? (Albeit a very small one)

Ok. I’ll shut up now. I realise this isn’t that huge a project and the physical constraints are pretty compromising but I would like to at least get it as “right” as I can with wasting a bunch of money that could be far better spend on hard drugs and strong alcohol.

Any thoughts/suggestions very much appreciated.


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PostPosted: Sun Feb 18, 2018 3:45 am 
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Hi there Pete, and Welcome! :)

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Here in London I have a small (4m x 3m) brick built outhouse that I want to convert into a basic studio to house a DAW and a small vocal/overdub booth.
12m2 is rather small to be able to fit in both a CR and an vocal booth. While I do normally recommend separate rooms when feasible, the key is "when feasible", and 12m2 is nor feasible. You'd probably be much better off with a single room. Vocals can be recorded successfully in a control room. The problem comes with trying to record some instruments that need more "ambiance". As long as it is just vocals, then tracking in the CR is possible.
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I’m thinking I will leave the floor well alone ...
:thu: Smart move!

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(Will probably carpet or put a laminate down when finished)
Forget carpet! It does the exact opposite of what you need for a small room. Carpet is a bad idea. Take a look at photos of high-end pro studios, and see how many are carpeted... There's a reason for that...

Also, if you plan to lay laminate flooring in top of ceramic tile, you'd better first check that your tile is very flat and level. If not, the laminate would eventually crack, and it would probably squeak and creak in the meantime. If it is not level, you'll need to level it.

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I’m looking at building a new skin inside the main structure comprising 4”x2” stud, rockwool in the cavity and probably 2 layers of 12mm plasterboard/gypsum. Electrics and lighting will all be surface mounted.
Good plan.

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. Am I correct in thinking that in order to avoid the dreaded 3 leaf effect it would be best to pull this old ceiling down and run additional rafters from my new stud walls, infill with rockwool and attach a couple of new layers of plasterboard to that?
That depends on how your roof is done. If the roof is totally sealed air-tight, and has decent mass on it, then yes, that would be the best way to proceed. BUt the vast majority of garage roof systems are not like that. Most are ventilated and low mass. Don't mess with a ventilated roof! You might indeed need to go with the dreaded 3-leaf system, which is not the end of the world. You can compensate.

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If possible, I would be looking at running the new ceiling rafters parrallel with and to drop a couple of inches below the existing ones in order to preserve the (minimal) ceiling height. Does this seem about right or am I missing something?
Consider going with an "inside-out" ceiling....

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The other bit was, is it worth running the floor plate for the new walls on neoprene?
No. You don't need high isolation, and it's really hard to ensure that the wall really will float. If you get it wrong, you wasted a lot of money and time. If you get it right, you gain a couple of dB of isolation, which you don't really need to gain anyway. Just seal the bottom plates to the floor with several beads of caulk, bolt it down, and you are done.

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Any thoughts/suggestions very much appreciated.
Post a rough but accurate layout of what you have right now, and of your thoughts on what you'd like to do, with dimensions, plus some photos of the actual room. That will help us understand better what it is you are facing.


- Stuart -

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PostPosted: Sun Feb 18, 2018 4:38 am 
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Cheers for the speedy response Stuart,

Point taken about having a single room and recording vocals in there. It's something I've done on quite a few occasions in other studios. (I've been an engineer in the UK since the mid nineties and have encountered many weird and wonderful recording situations). Two reasons for wanting to squeeze a booth in are 1/ I'm looking to bring in some commercial sessions and as cheesy as it might be, as well as being as functional as possible, the studio also has, to a certain extent at least, look the part, as far as visiting vocalists, etc are concerned. 2/ I will be recording a fair bit of rock guitar (some of it quite heavy) and although I know I don't need huge amounts of volume to get the kind of results I'm after, not having physical isolation is something I've struggled with in the past when I've had to record an amp/speaker in the control room. Yeah. The vocal booth would be tiny and that alone will create some weird resonances, etc, but I think for the purpose of this, although not ideal, it's something I have to go with.

No no to a carpeted floor then. That's fine. I checked the floor for level and it's fine. I don't think I'll have a problem laying a laminate over a basic underlay.

The roof - Hmm! Well, without pulling the ceiling down I can't really say for definite whether it's airtight, but yes, I doubt if it is and I also doubt if there's much mass there. The thing about the ceiling height is that, at the moment it's barely 2.1 metres high from the existing, tiled floor. Add 20mm or so of laminate and underlay plus new ceiling joists and a couple of layers of boards under the existing ceiling and we're talking a significant loss of ceiling height. I realise as far as a working situation goes, it's far from ideal, but having worked in a few other small studios with low ceilings, that slight claustrophobic feeling is something I'd want to avoid. (There are a couple of windows though, which I would retain and glaze again on the inner leaf, so maybe that would help with that a little).

Inside out ceiling - Yes. I am thinking about that. Same with the walls actually. I'm not that familiar with it though so will have a mooch about here to see what the pros and cons in my situation might be.

Neoprene under the wall floor plates - Yes. I get you on that. I do have a whole bunch of the stuff laying around from a previous build so it wouldn't cost me anything in terms of paying out for materials though. One of those things where I thought that maybe every little bit helps. Maybe I could restrict it to just being used in the iso booth that against your good and sensible advice I will probably end up building anyway. :)

Ok, it's dark here now so not the best time to take pics but maybe I'll try and take some tomorrow and stick them up so people can get the idea of what I'm working with.

Many thanks for your input. It's greatly appreciated.


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PostPosted: Sun Feb 18, 2018 9:08 am 
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As an attempt to make the situation a little clearer, here's a couple of shoddy diagrams of what's currently there and what I was thinking of doing....

Basically, I was considering glueing and battening a couple of layers of plasterboard to the plywood underside of the existing roof, then, in order to preserve as much ceiling height as possible, running parallel joists from my new stud walls with another couple of layers of plasterboard fixed to them with rockwool in the cavity. I realise this will make for a reflective ceiling but I can't really figure out how to do an "Inside Out" ceiling in this instance as it seems I don't have the original ceiling height to manouvre it all into place without dropping the eventual ceiling height even more. Though if anyone has any smart ideas I'm all ears......


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PostPosted: Sun Feb 18, 2018 9:57 am 
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Two reasons for wanting to squeeze a booth in are . . .
And the one reason why you really should not even try, is acoustics! :)

Google the following document: ITU BS.1116-3. Skip the first couple of chapters, as they are not applicable, but then carefully read the chapters on the minimum requirements for a critical listening room. Note: those are MINIMUM recommended specs.

That document is often used as the gold standard for designing control rooms. It fully defines what you need in order to have a usable control room. One of those parameters is the floor area of the room: 20m2 for stereo, 30 for multi-channel. Even if you do a single room, the floor area will still be less than half of the MINIMUM recommended size. It might, barely be possible, perhaps, maybe, to make that into a somewhat usable room, with slightly better than mediocre acoustics, by very careful design and construction, using every trick in the book to maximize acoustics. Perhaps. But if you cut it in half again, to about one quarter the minimum specified by BS.1116-3, do you REALLY think it will meet your own goal: "as well as being as functional as possible, the studio also has, to a certain extent at least, look the part"? Before you answer, get out a sheet of paper and draw it up, to scale. See how you will fit in two speakers that are at least 2.1m apart and at least 2.1m from the mix position, while still leaving 3m behind the mix position to the rear wall, where there's already 50cm of space taken up by the minimum possible amount of bass trapping such a room would absolutely need to even stand a remote chance of being usable, plus a desk, plus a couch for your client.... Please show how you would be able to fit all of that in to a room that measures around 3 to 4 m2. Would that really "look the part" of being a viable commercial studio? Would it really be "as functional as possible"? The answer is obviously a huge "no".

To get a better idea of just how tiny the room would be, and how non-functional it would be, and how it would certainly NOT look the part, here is a control room that we are busy tuning right now. Work in progress at present, advancing day by day: viewtopic.php?f=2&t=21368 The floor area of that room is about 17 m2 (already 5 m2 bigger than yours). It's one of the smallest I have designed, but I did take care to maximize the functionality, and the acoustics. It has modal support down to 40 Hz, which is not great but is still much lower than you would get with a room less than one third the size. I ask you, in all honesty, do you really think you could cut that room down to one third of its current size, and still have a usable control room? How would you be able to fit in everything you need (including the treatment)? Small rooms needs a huge amount of treatment. The smaller they are, the more they need. This is a simple fact, a simple consequence of the laws of physics, and there is no way around it. The acoustic response that the room MUST have is clearly outlined in BS.1116-3, and the only way to even get close to those specs, is with huge, massive, mountains of treatment. You can see how much space the treatment is taking already in that room I mentioned above, and we aren't done yet. But the owner knew from the start what the consequences of this design would be when I originally did it for him, a couple of years back. He was aware that the CR would be tight, but his priority was to maximize the size of the live room. We made the CR as small as we dared to go, and it will certainly be functional, and it will certainly look the part... but it's 50% larger than the total space you have available, and about 75% larger than the space you say you want.

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I will be recording a fair bit of rock guitar (some of it quite heavy) and although I know I don't need huge amounts of volume to get the kind of results I'm after, not having physical isolation is something I've struggled with in the past when I've had to record an amp/speaker in the control room.
Then don't put the amp in the control room! Put it in an isolation BOX, not an isolation BOOTH! It would be very possible to build an acoustically isolated box that is large enough to fit most amps in, as part of the room itself.

Quote:
Yeah. The vocal booth would be tiny ...,
You have worked with vocal talent before, clearly, so you are well aware of how finicky artists can be. Put a typical vocalist in a claustrophobic booth that they can only just stand up in, with no room for a music stand even, and see what type of reaction you get.... :)

Quote:
and that alone will create some weird resonances
You seem to be misunderstanding the acoustic issue here. The problem with very small rooms is NOT that they have weird resonances, but quite the contrary: they don't have enough! This is a very common mis-asumption, so don't kick yourself, but the truth is simple: the laws of physics describe how reverberance works, and it is very simple. Standing waves form between the walls of the room. The frequency where they form is dictated by the dimensions of the room. The lowest possible frequency is given by the longest dimension of the room. Each such standing wave is called a "room mode", and everyone knows that room modes are a problem, especially in small rooms. So far, so good. Not complex to understand. But now it gets bass-akwards from what many people assume. Here's how it REALLY works. I wrote this a while back for another forum member, so I'm cutting and pasting it here. I originally wrote it with reference to control rooms, so I'll add some more comments on the end with regard to iso booths.

---

Those "modes" (resonances) occur at very specific frequencies that are directly related to the distances between the walls. 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 changing to 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 76 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.

So let's go back to thinking about those room modes (also called "eigenmodes" sometimes): remember I said that they occur are 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!

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 home studio sizes), 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 your 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.

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, 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.

All of this leads to the question you didn't ask yet, but were 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 that 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 the 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.

---

OK, that's for normal sized control rooms that meet BS.1116-3 specs. Your room won't, even if you use all the space, so you WILL have a modal issue that extends up into the lower mid range. But your vocal booth is another story entirely: It won't have ANY MODES AT ALL in the low end, it will have some in the low mids, more in the mids, and plenty in the high mids and highs. So, seeing that you are an engineer, and understand the frequency spectrum of the human voice, think for a minute how a typical singer will sound in there: the lowest fundamental frequencies of the human voice will have no modal support at all in your booth, the first harmonics of some notes will, but few and far between, while others won't, and yet others will have better support. The second and higher harmonics will have support. So just imagine how you will apply EQ to such a vocal track! :!: 8) Answer: there is nothing you can do. Nothing at all.

This is why vocals recorded in tiny booths sound terrible. They always sound "boxy" and dull, no matter what you do. Because there is NO treatment that can improve the sound! If the room does not support modes, then it does not support modes, and there is NOTHING you can do to make it support modes! The track will ALWAYS sound boxy, dull, lifeless, and ugly, no matter what you do to the EQ. The ONLY solution is to add fake reverb from a much larger room in the mix. So every single vocal track you ever record will absolutely need to be drowned in fake reverb to make it usable. That does not fit your goal: "... being as functional as possible, ... look the part, as far as visiting vocalists, etc are concerned....". You cannot fool good vocalist: they know what type of acoustic response their voice needs to sound good. When a vocalist walks into your place, he or she will gasp in horror when you show them the broom closet, and tell them they have to sing or VO in there...

Here's what the modal response would be for a tiny booth, measuring 1.9m by 1.5 m, which is about as large as you would be able to fit in:
Attachment:
modal-response-tiny-booth--190-150-190.jpg


That's it. That's the response across the entire low end, and into the low mids, all the way up to 300 Hz. You have a grand total of five axial modes, very widely spaced, and ALL of them on sharps or flats. So any singer would sound off-key in there, even if they were singing spot on, simply because the modes would shift the apparent sound to the closest flat or sharp...

With a very small closet, then ONLY think you can do is to damp the hell out of it, with major absorption on most of the surfaces, and only one wall slightly reflective to at least retain some semblance of life, but it still sounds disgustingly terrible.

This is not just a subjective opinion: it is pure physics. The low order modal response of the room is what defines the entire acoustic "envelope" of the room. There is no way around this. No magical acoustic material, treatment or method that can make a small room sound large. It is physically impossible.

I would strongly urge you to sit down with SketchUp for a few hours, and do a simple modal of your studio, to see how it would work out. Start with your 4m x 3m space (which I'm assuming is the available floor space INSIDE the outhouse! I really hope that's not the size of the EXTERIOR!!!): So draw out a 4x3 m rectangle, then place walls that are 10cm thick, another 10cm away from the edges of that rectangle, to define actual available space. You will notice that it is not down to 3.8 long by 2.8 wide. Now split that in two, with another wall that is 20cm wide (10cm on each leaf). Let's say that you decide you can live with a vocal closet that is 1.6m deep, and that you want it to run the full 2.8 m width, to keep symmetry in the CR and attempt to maximize the sound of the booth. So you need to chop off 1.6 + 0.2 = 1.8m. So your control room will now be 2m wide by 2.8m long! :shock: Please try to fit in a desk, speakers, and a sofa into that, while keeping the speakers 2.1 apart from each other, at least 1m away from the side walls, 2.1 me from the mix position, and another 3m behind the mix position to the rear wall...

This is NOT a viable situation. Not by any measure. I've designed a lot of small studios over the years, but I would never even attempt to design a control room that is only 5.6 square meters, WITHOUT any treatment in it yet! There's no way it can be made usable. The laws of physics prevent it. The space you have simply is not large enough to do what you say you want.

Quote:
Add 20mm or so of laminate and underlay
:?: Why so thick? Underlay is commonly 2mm, and you can get good laminate at 8mm. 10mm max. With a very tiny space, you will need to do everything possible to maximize volume. For that size place, I would recommend not putting down any laminate, and just live with the ceramic tiles. That's a perfectly good floor for a studio.

Quote:
plus new ceiling joists and a couple of layers of boards under the existing ceiling and we're talking a significant loss of ceiling height.
Yes, but you don't have a choice! You can use higher density materials to save space, and use techniques such as inside-out construction to optimize acoustics. It's a VERY small space, even assuming that you keep it as one single room, so you will need to take extreme measures to eak out every last cubic mm of air volume. With good quality wood, you can span 2.8m with 2x4 joists, assuming typical loading and spacing. So you'd lose that, plus a little extra for the MSM gap and mass, and the visible ceiling could be at maybe 1.8m. But the actual acoustic ceiling could be at 1.9. With careful design, and high-density materials, you could probably gain another cm or so. That's still very low, but it is what it is. If you wanted to invest a bit more, you could probably modify the roof trusses to make them raised tie, or even collar tie, and gain quite a bit more. I've done that on a few studios, and the extra space is VERY useful, especially for your HVAC system (which you haven't even considered yet, but is very necessary).

Quote:
(There are a couple of windows though, which I would retain and glaze again on the inner leaf, so maybe that would help with that a little).
:thu: Not a problem! Natural light in a studio is a good thing.

Quote:
Inside out ceiling - Yes. I am thinking about that. Same with the walls actually. I'm not that familiar with it though so will have a mooch about here to see what the pros and cons in my situation might be.
For a small studio, it is all pro's, no con's, except for the increased complexity in construction. Its a bit harder to actual build it, but still within the realm of DIY.

Quote:
Neoprene under the wall floor plates - Yes. I get you on that. I do have a whole bunch of the stuff laying around from a previous build so it wouldn't cost me anything in terms of paying out for materials though. One of those things where I thought that maybe every little bit helps
Well, here's what you'd have to do: find out what the resilience or compliance of the rubber is, and use that to calculate how much it needs to deflect in order to create the correct resonant frequency. Then calculate what load you would have to apply in order to produce that amount of deflection, and cut the rubber to the correct size. In other words, the surface area of the rubber must be correct such that when the load of the walls and ceiling is resting on it, it deflects by the correct percentage, thus producing the correct resonant frequency so that the wall really will float, even when exposed to the lowest expected frequency that will occur in the room. The resonant frequency needs to be at least one octave lower than the lowest note, since the wall will not isolate for all frequencies between F0 and 1.414 x F0. It's not hard to do, but you do need to get into the math. And the prerequisite is that you have all the relevant data for the exact type of rubber that you have on hand.

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PostPosted: Sun Feb 18, 2018 10:00 am 
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As an attempt to make the situation a little clearer, here's a couple of shoddy diagrams of what's currently there and what I was thinking of doing....
Ahhh! So it's a FLAT roof! That's interesting. It probably is not vented then, which opens up new opportunities...

As long as you don't need very high isolation, you might be able to get away with beefing up under the deck, sealing well, then using clips and hat channel to hand your new inner-leaf ceiling. You could get upwards of 40 dB isolation like that, perhaps approaching 50 dB. And you would lose only a couple of cm of headroom, in total. It might be the best way to go.

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PostPosted: Mon Feb 19, 2018 5:41 am 
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Thanks again Stuart,

Didn’t think of using clips and channel, but of course. Yep. I think you’ve pointed the way to go there. If I can get 40+dB of isolation I’d be pretty happy. Am I correct in thinking that to bulk out the underside of the roof I’m best glueing the plasterboard to it as opposed to screwing it or is the difference likely to be negligible? Maybe green glue between the two new layers of boards?

Grr! Yep. You’ve convinced me that a single room is the best way to go. :) Just have to start getting on with it now really. Will start to remove the lighting and take down the existing crappy ceiling tomorrow and see what I’ve got to work with.

Regarding the clips and channel, I’ve used Genie Clips before which kinda worked ok though they seemed a bit expensive. (Now looking at around £400 for a pack of 100) Anyone have any thoughts on these? https://www.sruinsulation.co.uk/product-list/decoupling-brackets-metal/Geni-Clip-box The specs do seem quite good but can’t help wondering if there is something cheaper that would do “almost” as good a job.


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PostPosted: Wed Mar 21, 2018 6:10 am 
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Very informative thread.

Stuart, is your little section on modal resonance a sticky somewhere? I'd like to reference it later, and also show a few friends who like to get into this stuff too.

Also, you said the ceiling construction that Pete was thinking about (and is in Rod's book) would get him 40, maybe 50dB of isolation. Is that number from experience mostly? Or how can that be calculated to maximize isolation? I'm in a similar situation with my basement ceiling, so am most likely going to do the same thing.

Thanks!


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PostPosted: Wed Mar 21, 2018 7:00 am 
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Regarding the clips and channel, I’ve used Genie Clips before which kinda worked ok though they seemed a bit expensive. (Now looking at around £400 for a pack of 100) Anyone have any thoughts on these? https://www.sruinsulation.co.uk/product-list/decoupling-brackets-metal/Geni-Clip-box The specs do seem quite good but can’t help wondering if there is something cheaper that would do “almost” as good a job.


If you have amazon available to you, that is where I found the best deals
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PostPosted: Sat Mar 24, 2018 3:15 am 
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Stuart, is your little section on modal resonance a sticky somewhere? I'd like to reference it later, and also show a few friends who like to get into this stuff too.
I just made this thread a sticky! When I have time, I plan to do several stand-alone stickies in the reference area, with commonly used info, such as this.

Quote:
Also, you said the ceiling construction that Pete was thinking about (and is in Rod's book) would get him 40, maybe 50dB of isolation. Is that number from experience mostly? Or how can that be calculated to maximize isolation? I'm in a similar situation with my basement ceiling, so am most likely going to do the same thing.
Mostly from experience, but it can be calculated. It's a two-leaf MSM system, so there's a set of equations that can be used to figure that out. Once again, here's something I wrote for another thread a while back (and it should also be a sticky on it's own!):


----------

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.


--------

Greg actually created a spreadsheet that will do all of this for you, but I don't have the link on hand right now... Maybe Greg will see this, and add the link ...



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PostPosted: Sat Mar 24, 2018 4:38 am 
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Ah, right. I have that spreadsheet and use it. I got in my head and was thinking of the ceiling as a single leaf, because usually on here we're talking 2 leaves as in 2 walls. But the ceiling being a simple 2 leaf makes perfect sense.

I know the RC clips reduce flanking a little bit between ceiling and floor which share joists, but how do you account for that in the MSM equation, where there isn't a solid air (or insulation filled) air gap?

As always, thanks Stuart!


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PostPosted: Sat Jun 16, 2018 12:35 pm 
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I know the RC clips reduce flanking a little bit between ceiling and floor which share joists, but how do you account for that in the MSM equation, where there isn't a solid air (or insulation filled) air gap?
I'm not sure I understand the question: There is still an air gap, exactly the same as for any other two-leaf wall. The air gap is still the distance across the cavity between the face of the drywall on one side of the cavity, and the face of the drywall on the other side of the cavity.

So, to account for the extra depth of the RSIC plus hat channel (or for RC by itself) in the MSM equations, you just add the thickness. Thus, for RC, you would use the stud depth plus the thickness fo the RC, and that would be your cavity depth. And for RSIC + hat channel, you would add the stud depth pus the thickness of the clip of the clip plus the thickness of the hat, and that would be your cavity depth.

All you are doing is to slightly increase the depth of the air cavity, while also decoupling.

However, there's a limit with RC and with clips: they are much more stiff than air, so you are limited to a total improvement of about 15 dB, with respect to the wall that is NOT decoupled, so if your calculations show an improvement of more than 15 dB, then you should round that off.

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