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PostPosted: Sun Oct 01, 2017 6:08 pm 
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Posts: 4
Location: Adelaide
Howdy,
I've been a long time lurker and this is my first post. Great forum. I'm in Adelaide, South Australia and record mostly blues and folk.
I searched the forum but may have used the wrong search terms as I couldn't much info on this..

I've started rebuilding my space downstairs, and the ceiling is 150mm concrete with the house living space above. I've had quite a lot of quite quiet leakage through the edges of the slab I think (the room is under the corner of the slab) so I've hung Rondo acoustic mounts for slabs and am hanging 16mm Gyprock Firecheck from the furring channels that clip into them. Once thats done, I'll seal the edges with Fuller fyrecheck/acoustic sealant and then hang gyprock on the walls on Rondo isolation channel up to the ceiling gyprock and seal the edges with the same stuff. It's really soft and 1/2 the cost of green glue.
I should add, the front wall is 300mm concrete, the l/h side wall is 300mm solid stone, the r/h wall is besa brick that I havent treated yet, because I'm not sure how to 'mass it up', the rear wall is a double glazed timber door, 3 double glazed windows 300w by 600h sitting on a waist high wall made of besser brick, and the floor is concrete. the idea is to soffit mount the monitors by mounting them to the concrete wall and fitting the flush by mounting that the wall and a large 300 x 600 footing that extends out from the front wall. It's very solid and the speaker soffit mount should be fine.
In a nutshell, 3.2w x 6l x 2.65h, concrete, soffit mounted and splayed..Anyway, ..
I've only allowed about 60mm gap between the inside of the ceiling gyprock and the slab, and was going to put 60mm acoustic insulation in there and now I have a question if anyone can help.

Will insulation touching the concrete ceiling and the hanging gyprock transfer sound to the slab or is that a myth?
Sorry if I haven't given enough information..

Anyway, thanks in advance!
Cheers
Steve

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PostPosted: Mon Oct 02, 2017 10:42 am 
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Location: Santiago, Chile
Hi Steve, and Welcome to the forum! :)

Quote:
In a nutshell, 3.2w x 6l x 2.65h,
That's to the original concrete walls, floor, and ceiling, correct?

Quote:
so I've hung Rondo acoustic mounts for slabs
Which specific product did you use? They make several.

Quote:
I'll seal the edges with Fuller fyrecheck/acoustic sealant ... It's really soft and 1/2 the cost of green glue.
Are you sure you are comparing apples to apples? Green Glue Compound is not sealant. The Green Glue company also makes a sealant product, but their famous Green Glue Compound, which is expensive, is not it. The compound is something else entirely.

Quote:
the r/h wall is besa brick that I havent treated yet, because I'm not sure how to 'mass it up',
Plaster, then paint. Use any good quality interior wall plaster, designed for use on masonry. Put a reasonably thick layer on, then paint it it when it is dry, for the best seal. Also paint all of your concrete surfaces using a good quality concrete or masonry sealant, before you do anything at all to them. Concrete is porous, and that needs to be sealed for good isolation.

Quote:
the rear wall is a double glazed timber door,
Ooops! There's your weak point. Pity about that. Otherwise you could have had really good isolation.

Which leads to the question: How much isolation do you need? What is your goal, in terms of decibels of isolation (transmission loss)?

Quote:
the idea is to soffit mount the monitors by mounting them to the concrete wall and fitting the flush by mounting that the wall and a large 300 x 600 footing that extends out from the front wall.
It seems you have misunderstood what flush mounting (soffit mounting) actually is. The point is that you need to create an "infinite baffle" in the same plane as the existing front baffle of the speaker cabinet itself, and that baffle has to be at the correct angle for the room. The speakers are not mounted directly to the walls. They are mounted inside a "module", that normally consists of hefty, rigid framing that supports the speaker and also the baffle, possibly with the speaker decoupled from the framing if you want to go that route.

Quote:
It's very solid and the speaker soffit mount should be fine.
It will only be fine if it is designed correctly! :) Soffits are not extremely complicated, but they are more complicated than what you are describing. Here's a set of soffits under construction for a studio I designed for one of my customers a few years ago:
Attachment:
BUILD-02nd-construction-all-soffits--2012-12-08-photo 1-SML-ENH-ENH.JPG


And here's how the room turned out in the end: viewtopic.php?f=2&t=20471 .


Quote:
I've only allowed about 60mm gap between the inside of the ceiling gyprock and the slab,
That's a rather small gap! The general recommendation is to never have an MSM gap that is smaller than about 100 mm, since the resonant frequency gets too high, and isolation can suffer. Did you check that your setup is still going to give you the isolation you need, at the frequencies where you need it?

Quote:
Will insulation touching the concrete ceiling and the hanging gyprock transfer sound to the slab or is that a myth?
Myth. Assuming that you use the correct insulation, and that you don't jam it in tightly, there's no problem if it touches both sides. Im fact, you NEED to fill the entirely cavity (loosely) for maximum isolation. It only becomes a problem if the insulation is too dense, or it if it is compressed to force it into the cavity. In other words, 60mm of uncompressed insulation in a 60mm cavity us just fine, but 100 mm of insulation forced into a 60mm cavity is definitely not fine.

- Stuart -


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PostPosted: Thu Oct 05, 2017 4:50 pm 
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Soundman2020 wrote:
Hi Steve, and Welcome to the forum! :)

Thanks very much! It's a great place to lurk :)

Quote:
In a nutshell, 3.2w x 6l x 2.65h,
That's to the original concrete walls, floor, and ceiling, correct?

Yes correct.

Quote:
so I've hung Rondo acoustic mounts for slabs
Which specific product did you use? They make several.

I'm using STSL 65 acoustic hangers with furring channel.

Quote:
I'll seal the edges with Fuller fyrecheck/acoustic sealant ... It's really soft and 1/2 the cost of green glue.
Are you sure you are comparing apples to apples? Green Glue Compound is not sealant. The Green Glue company also makes a sealant product, but their famous Green Glue Compound, which is expensive, is not it. The compound is something else entirely.

The sealant is a very soft fire/acoustic sealant for between concrete panels when making apartments. It's a regular feature here in Australia. I'm surprised more people don't know about it. It is a good system from what I understand. Fuller Firesound™

Quote:
the r/h wall is besa brick that I havent treated yet, because I'm not sure how to 'mass it up',
Plaster, then paint. Use any good quality interior wall plaster, designed for use on masonry. Put a reasonably thick layer on, then paint it it when it is dry, for the best seal. Also paint all of your concrete surfaces using a good quality concrete or masonry sealant, before you do anything at all to them. Concrete is porous, and that needs to be sealed for good isolation.

Thanks!

Quote:
the rear wall is a double glazed timber door,
Ooops! There's your weak point. Pity about that. Otherwise you could have had really good isolation.

I don't need BIG isolation as I've made an airlock past the back wall, but also I don't want heaps of mass at the back because I'm doing a design that needs the bass (and high frequencies really) to pass my head once and never come back if possible :D
The room will be soft with a hard reflective soffit mount so it's not like living in a ball of cotton wool. Tell me if I've gone off the rails here.
The idea is to make a NE type room, I'm even toying with the idea of pulling the back wall out and making an 8 foot deep wide band trap. Not sure yet.


Which leads to the question: How much isolation do you need? What is your goal, in terms of decibels of isolation (transmission loss)?

I don't know how to calculate that, maths is not my strong point. I don't operate much above 90dB in the control room. It's the lower level of my house, and I was hoping to keep it looking fairly "normal" as far as the walls go. Soffit, clouds (if any) and bolt on stuff doesn't matter as I can take it down if I ever need to sell the house.

Quote:
the idea is to soffit mount the monitors by mounting them to the concrete wall and fitting the flush by mounting that the wall and a large 300 x 600 footing that extends out from the front wall.
It seems you have misunderstood what flush mounting (soffit mounting) actually is. The point is that you need to create an "infinite baffle" in the same plane as the existing front baffle of the speaker cabinet itself, and that baffle has to be at the correct angle for the room. The speakers are not mounted directly to the walls. They are mounted inside a "module", that normally consists of hefty, rigid framing that supports the speaker and also the baffle, possibly with the speaker decoupled from the framing if you want to go that route.

Ok, I thought I could isolate the speakers by mounting them on a structure that is so heavy it will never vibrate. Then make the front (baffle) on another structure that is so heavy it will never vibrate and then speaker and baffle will be completely isolated from each other and that's correct. But I'm wrong? I understand the infinite baffle idea, I thought I had it right? Maybe I should try Sketchup in case I'm not describing it properly. My idea is to make the baffle with 4 x 25mm MDF sheets with goo between them and fill the cavity with R5 insulation.

Quote:
It's very solid and the speaker soffit mount should be fine.
It will only be fine if it is designed correctly! :) Soffits are not extremely complicated, but they are more complicated than what you are describing. Here's a set of soffits under construction for a studio I designed for one of my customers a few years ago:
Attachment:
BUILD-02nd-construction-all-soffits--2012-12-08-photo 1-SML-ENH-ENH.JPG


And here's how the room turned out in the end: viewtopic.php?f=2&t=20471 .

Yes, I looked at that thread with great interest. Very nice work!


Quote:
I've only allowed about 60mm gap between the inside of the ceiling gyprock and the slab,
That's a rather small gap! The general recommendation is to never have an MSM gap that is smaller than about 100 mm, since the resonant frequency gets too high, and isolation can suffer. Did you check that your setup is still going to give you the isolation you need, at the frequencies where you need it?

I could probably get 80mm if I tried harder, it'll mean muscling all the furring channel out of the clips :p

Quote:
Will insulation touching the concrete ceiling and the hanging gyprock transfer sound to the slab or is that a myth?
Myth. Assuming that you use the correct insulation, and that you don't jam it in tightly, there's no problem if it touches both sides. Im fact, you NEED to fill the entirely cavity (loosely) for maximum isolation. It only becomes a problem if the insulation is too dense, or it if it is compressed to force it into the cavity. In other words, 60mm of uncompressed insulation in a 60mm cavity us just fine, but 100 mm of insulation forced into a 60mm cavity is definitely not fine.

OK then. I'll get 80mm and put 70mm in it. It'll also have a soft ceiling with Dunlop gray acoustic 100mm attached to it on the underside.
Thanks so much for your help. I've had analysis paralysis for ages and am a bit stuck..

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MTE console, Quad Eight dynamics, old school outboard with 2" and digital.


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PostPosted: Fri Oct 06, 2017 3:05 am 
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Quote:
I don't need BIG isolation as I've made an airlock past the back wall, but also I don't want heaps of mass at the back because I'm doing a design that needs the bass (and high frequencies really) to pass my head once and never come back if possible
You seem to be confusing isolation with treatment. And while Philip Newell says a lot of good stuff in his books, there's also some "out there" stuff that isn't supported by research. For example, I'm not sure why anyone would want to unbalance the overall response of a room at the expense of the overall isolation... that's a "lose-lose" situation!

Quote:
The room will be soft with a hard reflective soffit mount so it's not like living in a ball of cotton wool. Tell me if I've gone off the rails here.
You should probably take a look at the document ITU BS.1116-3, which is THE go-to reference for the technical specifications of a critical listening room. It defines exactly what the response of the room should be, if you plan to use it as a control room. You'll notice that above all, it specifies balance, and smoothness: any place you look in the entire audible spectrum, from 20 Hz to 20 kHz, should have the exact same response as any other part of the spectrum. For example, there can be no difference in decay times that is greater than 0.05 seconds between adjacent 1/3 octave bands. There can be no difference in SPL level that exceeds 3 dB between any two points on the spectrum. etc. Since the raw response of your untreated room will look like the mountains of Mars (especially below the Schroeder frequency!), you will need to have specific treatment devices for each frequency range that will control not just the frequency, but also the way that frequency decays over time, and also how the phase and timing of that frequency are affected.

Here's what the acoustic response of a room looks like, when it fully meets that spec: viewtopic.php?f=2&t=20471 I know you've already seen that, but take another look. It would not have been possible to achieve that result if I would have designed the room with no rear wall.... :) You'll notice that the acoustic response is perfectly balanced, smooth, and even across the entire spectrum, in both the frequency domain as well as the time domain, which is actually more important than the frequency domain. That's what you should be aiming for in your room. You can only get there if your design is balanced, and treats each part of the musical spectrum specifically for what it needs. Lows are very, very different from highs, and mids are different again. Each frequency band needs to be dealt with in its own specific manner.

Quote:
The idea is to make a NE type room,
Personally, I much prefer the RFZ concept. You'll notice that most of John's designs are base on RFZ, as are the designs of many other highly respected designers.

Quote:
I'm even toying with the idea of pulling the back wall out and making an 8 foot deep wide band trap. Not sure yet.
If it is possible to extend your room 8 feet further back, and dedicate a lot of that to bass trapping, then I'd certainly consider it, seriously! But not if it would cost you isolation. Rooms should be FIRST isolated, and when that is totally completed, only THEN they should be treated. They are two entirely different aspects of acoustics, and therefore also of studio design. Some people try to lump them together, but they are very different things. Opposites, in many ways. Treatment for a room can only be correctly designed once the raw acoustic response of the room is known, and that cannot be known until the room has been isolated to the desired level.

Also, it would be a mistake to make the entire rear end of your room into a broad-band trap: The LEDE concept was tried and abandoned decades ago. It was abandoned because it was uncomfortable, unnatural, and fatiguing. RFZ is an extension of LEDE that gets rid of all the bad parts, and enhances the good parts. It produces a balanced room that is neutral and pleasant to work in for long periods. So your rear wall should NOT attempt to suck the life out of the room! It should control the bass, definitely, it should deal with SBIR and modal issues associated with the primary axis, absolutely, but it should also return a diffuse, even, smooth reverberant field to your ears, delayed by at least the Haas time, and that field should then die away smoothly at the correct rate for the overall volume of the room, relative to the "standard" volume.

The concept is that the room should be neutral, neither add to nor subtract from the direct sound of the speakers.

Quote:
I don't know how to calculate that, maths is not my strong point.
Can you subtract? :) If you hand the check-out clerk at the supermarket a hundred dollar bill for your groceries that cost 85 dollars, can you figure out how much change you should get? :) That's all the math you need here. Get a decent quality sound level meter (they are not expensive), measure how loud you are in a typical recording session, measure how quite it is outside your building late at night when there is only background noise from the neighborhood around. Subtract. That's how much isolation you need.

Quote:
I don't operate much above 90dB in the control room.
dBA or dBC? There's a large difference!

Quote:
I was hoping to keep it looking fairly "normal" as far as the walls go. Soffit, clouds (if any) and bolt on stuff doesn't matter as I can take it down if I ever need to sell the house.
Ummm... OK, that's fine, but how do you reconcile that with "pull the back wall out and make an 8 foot deep wide band trap."? That seems like just a bit more than "looking fairly normal"... :)

Quote:
Ok, I thought I could isolate the speakers by mounting them on a structure that is so heavy it will never vibrate.
But you said you were planning on mounting the speakers to the walls! Walls vibrate. If you don't think they do, then tap your wall gently with a small hammer, and listen....

Quote:
Then make the front (baffle) on another structure that is so heavy it will never vibrate
It's not just about being heavy: it also needs to be rigid, and damped. All three aspects go together. Both for the speaker and for the soffit.

Quote:
and then speaker and baffle will be completely isolated from each other and that's correct.
That's one way of doing it, yes, and that's the way I prefer personally, but there's an alternative method that other people use. For example, John prefers to mount both the baffle and the speaker very rigidly to the same massive, rigid, damped structure, rather than different structures. That also works. Personally, I just float the speaker on carefully tuned and damped isolation mounts, within the massive, rigid, damped structure that supports both the speaker and the baffle. That's the method that makes the most sense for me, and I have used it successfully in many studios that I have designed, where the owner has wanted to do that.
Quote:
Maybe I should try Sketchup in case I'm not describing it properly.
:thu: that would certainly help to understand it better, and see if you are doing it correctly.

Quote:
My idea is to make the baffle with 4 x 25mm MDF sheets with goo between them and fill the cavity with R5 insulation.
Question: Your baffle will be 4 inches thick (100mm), which implies that the front 4 inches of your speaker will have zero support (since with your plan, the speaker cannot touch the baffle: How do you plan to support your speaker from ONLY the rear section? You cannot support it at any point of the front four inches, so what system do you have in mind for supporting it in such a way that it is held absolutely rigidly, yet not in the front 4"?

Also, why did you choose R5 insulation? Did you check if the acoustic properties would be suitable for damping the internal resonances that will occur inside the soffit? How will you cool and ventilate the speaker, if it is surrounded with thick insulation on all sides?

These are all things that first-time soffit designers don't think about until they are wall advanced with their designs, and notice the major problems they are creating for themselves, so I'm bringing them to your attention early in the process, such that you can take them al into account right from the start as you work on your soffit design.

Quote:
I could probably get 80mm if I tried harder, it'll mean muscling all the furring channel out of the clips
Don't guess: do the math to make sure that you really will get the correct MSM resonance frequency, and the amount of isolation that you need, at the frequencies where you need it. Here's what you need to know:

The equations for calcualting 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.

Quote:
It'll also have a soft ceiling with Dunlop gray acoustic 100mm attached to it on the underside.
I'm not familiar with that product. I googled that exact term, and found nothing: just references to suppressor covers for acoustic guitar sound holes ( https://varietymusic.com.au/products/el ... e-shipping ), and also for guitar picks, but nothing on acoustic treatment products. Do you have a link to the specs for that product?

Assuming that you are referring to some type of porous absorber product that you plan to have below your hard inner-leaf ceiling surface, that's fine, but it does nothing at all to improve isolation. That's treatment, not isolation. If it is inside the room, then it cannot help with isolation, so it must be treatment. If it is inside the wall (part of the wall system) then it is isolation, and cannot help with treatment. As I mentioned above, those are two entirely separate and distinct parts of acoustics, and also of room design. They can only be combined to a very limited extent. The basic rule is that the isolation of the room will play a part in dictating what treatment will be needed in the room, but the isolation is not treatment, and the treatment is not isolation.

If you don't agree that typical soft insulation products are no use for isolation, then take a 2 inch thick piece of fiberglass or mineral wool insulation, tape it across the front of your favorite speaker, and turn up the volume... Can you still hear the speaker? Yup, you sure can! The porous absorption did very little to reduce the overall level. All that it did was to take the edge of the high end, but the low end still pumps through, as loud as ever. In fact, you can even do this test to see just how much effect it does have: set your speaker to produce 100 dBC with typical bass-heavy rock music WITHOUT the insulation covering it, then put the insulation over it and see what the remaining level is... I think you'll be surprised! Because insulation is not isolation: it is treatment.

Think of it this way: If you accidentally splash some water in your kitchen some place that you didn't want it, then a sponge is a great way of moping that up. But if you turn on the tap and hold the sponge over the end, it does nothing at all to stop the water flowing through. Insulation is the same: great for mopping up sound that splashed some place you didn't want it (treatment) but useless for stopping sound from getting out of the room (isolation).

Quote:
Thanks so much for your help. I've had analysis paralysis for ages and am a bit stuck..
:thu: That's what we are here for! :)

- Stuart -

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PostPosted: Fri Oct 06, 2017 10:30 pm 
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Soundman2020 wrote:
Quote:
I don't need BIG isolation as I've made an airlock past the back wall, but also I don't want heaps of mass at the back because I'm doing a design that needs the bass (and high frequencies really) to pass my head once and never come back if possible
You seem to be confusing isolation with treatment. And while Philip Newell says a lot of good stuff in his books, there's also some "out there" stuff that isn't supported by research. For example, I'm not sure why anyone would want to unbalance the overall response of a room at the expense of the overall isolation... that's a "lose-lose" situation!

Yep OK. What I meant was, I didn't want heaps of hard mass to bounce things back at me. I have access to a Newell type studio here in Adelaide, and it is really very good. You can stand anywhere in the room and it's pretty great. Even with old JBL's, I heard 20hz for the first time. Not fatiguing either, and the guy who owns it does a lot of National broadcast including state orchestra etc. I'm certainly not arguing with you, I'm just going with what I've learnt so far and I've got a ways to go. The whole Newell NE thing is based on the assumption that my room is really a tad too small and I'm not very wealthy, so it seemed a good way to go from those 2 perspectives, but I'm totally open to your expertise in this area.

Quote:
The room will be soft with a hard reflective soffit mount so it's not like living in a ball of cotton wool. Tell me if I've gone off the rails here.
You should probably take a look at the document ITU BS.1116-3, which is THE go-to reference for the technical specifications of a critical listening room. It defines exactly what the response of the room should be, if you plan to use it as a control room. You'll notice that above all, it specifies balance, and smoothness: any place you look in the entire audible spectrum, from 20 Hz to 20 kHz, should have the exact same response as any other part of the spectrum. For example, there can be no difference in decay times that is greater than 0.05 seconds between adjacent 1/3 octave bands. There can be no difference in SPL level that exceeds 3 dB between any two points on the spectrum. etc. Since the raw response of your untreated room will look like the mountains of Mars (especially below the Schroeder frequency!), you will need to have specific treatment devices for each frequency range that will control not just the frequency, but also the way that frequency decays over time, and also how the phase and timing of that frequency are affected.

Yep, and because there is 2 doors in corners, I assumed there was no room for treatment, hence the dead zone in the end of the room idea, but now that I've realised I could just undo some work that I've done, I could gain 2 metres. Bit confused, I'll do a SKetch and see how I feel about it..

Here's what the acoustic response of a room looks like, when it fully meets that spec: http://www.johnlsayers.com/phpBB2/viewt ... =2&t=20471 I know you've already seen that, but take another look. It would not have been possible to achieve that result if I would have designed the room with no rear wall.... :) You'll notice that the acoustic response is perfectly balanced, smooth, and even across the entire spectrum, in both the frequency domain as well as the time domain, which is actually more important than the frequency domain. That's what you should be aiming for in your room. You can only get there if your design is balanced, and treats each part of the musical spectrum specifically for what it needs. Lows are very, very different from highs, and mids are different again. Each frequency band needs to be dealt with in its own specific manner.

I understand this.

Quote:
The idea is to make a NE type room,
Personally, I much prefer the RFZ concept. You'll notice that most of John's designs are base on RFZ, as are the designs of many other highly respected designers.

OK, I hear what you're saying

Quote:
I'm even toying with the idea of pulling the back wall out and making an 8 foot deep wide band trap. Not sure yet.
If it is possible to extend your room 8 feet further back, and dedicate a lot of that to bass trapping, then I'd certainly consider it, seriously! But not if it would cost you isolation. Rooms should be FIRST isolated, and when that is totally completed, only THEN they should be treated. They are two entirely different aspects of acoustics, and therefore also of studio design. Some people try to lump them together, but they are very different things. Opposites, in many ways. Treatment for a room can only be correctly designed once the raw acoustic response of the room is known, and that cannot be known until the room has been isolated to the desired level.

Also, it would be a mistake to make the entire rear end of your room into a broad-band trap: The LEDE concept was tried and abandoned decades ago. It was abandoned because it was uncomfortable, unnatural, and fatiguing. RFZ is an extension of LEDE that gets rid of all the bad parts, and enhances the good parts. It produces a balanced room that is neutral and pleasant to work in for long periods. So your rear wall should NOT attempt to suck the life out of the room! It should control the bass, definitely, it should deal with SBIR and modal issues associated with the primary axis, absolutely, but it should also return a diffuse, even, smooth reverberant field to your ears, delayed by at least the Haas time, and that field should then die away smoothly at the correct rate for the overall volume of the room, relative to the "standard" volume.

The concept is that the room should be neutral, neither add to nor subtract from the direct sound of the speakers.

[color=#FF0000]I understand what you're saying, the whole building is concrete, so isolation should not be too hard really. Problem is I started building the studio before I really understood what was required. Now I'm erring toward pulling out a wall and starting again. Again, I'll do a sketch up.[/color]

Quote:
I don't know how to calculate that, maths is not my strong point.
Can you subtract? :) If you hand the check-out clerk at the supermarket a hundred dollar bill for your groceries that cost 85 dollars, can you figure out how much change you should get? :) That's all the math you need here. Get a decent quality sound level meter (they are not expensive), measure how loud you are in a typical recording session, measure how quite it is outside your building late at night when there is only background noise from the neighborhood around. Subtract. That's how much isolation you need.

Quote:
I don't operate much above 90dB in the control room.
dBA or dBC? There's a large difference!

87dBA was my comfortable listening level. I live in an area where neighbours are more likely to bother me that me them.

Quote:
I was hoping to keep it looking fairly "normal" as far as the walls go. Soffit, clouds (if any) and bolt on stuff doesn't matter as I can take it down if I ever need to sell the house.
Ummm... OK, that's fine, but how do you reconcile that with "pull the back wall out and make an 8 foot deep wide band trap."? That seems like just a bit more than "looking fairly normal"... :)

I can remove a stack of material, and I think my version of normal might be subjective :)

Quote:
Ok, I thought I could isolate the speakers by mounting them on a structure that is so heavy it will never vibrate.
But you said you were planning on mounting the speakers to the walls! Walls vibrate. If you don't think they do, then tap your wall gently with a small hammer, and listen....

OK, so my 'wall' is 350mm thick poured concrete. I can mount speakers to that without fear of vibration.

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Then make the front (baffle) on another structure that is so heavy it will never vibrate
It's not just about being heavy: it also needs to be rigid, and damped. All three aspects go together. Both for the speaker and for the soffit.

Agreed, I make acoustic guitars for a living so I understand the concept. I can stand the baffle on 600x300mm concrete and mount the supporting struts to a 350mm concrete wall and still have no vibration issues that I can see. Again, I think Sketchup will help. I'm sure what I have in my head is OK :p

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and then speaker and baffle will be completely isolated from each other and that's correct.
That's one way of doing it, yes, and that's the way I prefer personally, but there's an alternative method that other people use. For example, John prefers to mount both the baffle and the speaker very rigidly to the same massive, rigid, damped structure, rather than different structures. That also works. Personally, I just float the speaker on carefully tuned and damped isolation mounts, within the massive, rigid, damped structure that supports both the speaker and the baffle. That's the method that makes the most sense for me, and I have used it successfully in many studios that I have designed, where the owner has wanted to do that.
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Maybe I should try Sketchup in case I'm not describing it properly.
:thu: that would certainly help to understand it better, and see if you are doing it correctly.

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My idea is to make the baffle with 4 x 25mm MDF sheets with goo between them and fill the cavity with R5 insulation.
Question: Your baffle will be 4 inches thick (100mm), which implies that the front 4 inches of your speaker will have zero support (since with your plan, the speaker cannot touch the baffle: How do you plan to support your speaker from ONLY the rear section? You cannot support it at any point of the front four inches, so what system do you have in mind for supporting it in such a way that it is held absolutely rigidly, yet not in the front 4"?

I think I have that worked out. I can hang a solid steel shelf per speaker straight off the back 350mm concrete wall and it will hold itself up with a bracket under it. Like a spiral staircase if you know what those treads look like.. .

Also, why did you choose R5 insulation? Did you check if the acoustic properties would be suitable for damping the internal resonances that will occur inside the soffit? How will you cool and ventilate the speaker, if it is surrounded with thick insulation on all sides?

I guessed. Sorry! My speakers are passive at the moment, but I looked at Johns design for soffit and thought I'd manage air flow if I needed to.

These are all things that first-time soffit designers don't think about until they are wall advanced with their designs, and notice the major problems they are creating for themselves, so I'm bringing them to your attention early in the process, such that you can take them al into account right from the start as you work on your soffit design.

Thankyou!!

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I could probably get 80mm if I tried harder, it'll mean muscling all the furring channel out of the clips
Don't guess: do the math to make sure that you really will get the correct MSM resonance frequency, and the amount of isolation that you need, at the frequencies where you need it. Here's what you need to know:

The equations for calcualting 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.

I'll give it a go

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It'll also have a soft ceiling with Dunlop gray acoustic 100mm attached to it on the underside.
I'm not familiar with that product. I googled that exact term, and found nothing: just references to suppressor covers for acoustic guitar sound holes ( https://varietymusic.com.au/products/el ... e-shipping ), and also for guitar picks, but nothing on acoustic treatment products. Do you have a link to the specs for that product?

I don't think they make it anymore!! I tried to find it as well! It's what I have anyway, it's super absorbent.


Assuming that you are referring to some type of porous absorber product that you plan to have below your hard inner-leaf ceiling surface, that's fine, but it does nothing at all to improve isolation. That's treatment, not isolation. If it is inside the room, then it cannot help with isolation, so it must be treatment. If it is inside the wall (part of the wall system) then it is isolation, and cannot help with treatment. As I mentioned above, those are two entirely separate and distinct parts of acoustics, and also of room design. They can only be combined to a very limited extent. The basic rule is that the isolation of the room will play a part in dictating what treatment will be needed in the room, but the isolation is not treatment, and the treatment is not isolation.

Yep, I have the Gervais book on studio design and was looking at that. I do get the difference, I just didn't articulate it very well.

If you don't agree that typical soft insulation products are no use for isolation, then take a 2 inch thick piece of fiberglass or mineral wool insulation, tape it across the front of your favorite speaker, and turn up the volume... Can you still hear the speaker? Yup, you sure can! The porous absorption did very little to reduce the overall level. All that it did was to take the edge of the high end, but the low end still pumps through, as loud as ever. In fact, you can even do this test to see just how much effect it does have: set your speaker to produce 100 dBC with typical bass-heavy rock music WITHOUT the insulation covering it, then put the insulation over it and see what the remaining level is... I think you'll be surprised! Because insulation is not isolation: it is treatment.

Think of it this way: If you accidentally splash some water in your kitchen some place that you didn't want it, then a sponge is a great way of moping that up. But if you turn on the tap and hold the sponge over the end, it does nothing at all to stop the water flowing through. Insulation is the same: great for mopping up sound that splashed some place you didn't want it (treatment) but useless for stopping sound from getting out of the room (isolation).

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Thanks so much for your help. I've had analysis paralysis for ages and am a bit stuck..
:thu: That's what we are here for! :)

Thanks again! Before I go, you mentioned plastering up the besser block wall with a heavy plaster to 'mass it up', but would 3 layers of cement sheet do the same at 9mm each? It would be MUCH easier for me to do as the access to flat ground outside is difficult and mixing mud is hard work and plastering is highly skilled.

Thanks again for your input

Steve


- Stuart -

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MTE console, Quad Eight dynamics, old school outboard with 2" and digital.


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PostPosted: Fri Oct 06, 2017 10:52 pm 
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I'm having a red hot go at Sketchup. Bit of a learning curve, I'll do more tomorrow, it's late here now.
Cheers
Steve

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PostPosted: Sat Oct 07, 2017 2:36 am 
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Quote:
What I meant was, I didn't want heaps of hard mass to bounce things back at me.
That's what I'm talking about, actually: Mass is what you need to isolate the room, and to create the inner-leaf surface, which is the acoustic boundary of the room. That's what sets the overall acoustic "signature" of the room. It governs what the lowest modal support frequency will be, which in turn governs how the room will perform. It defines the "shape" of the acoustic response that the room will have, and it puts a lower boundary on how low your Schroeder frequency can go. So it's important to have the rear-wall mass in the correct location. That's part of what "room ratio" is about. Yes, one unfortunate side effect of having a good solid rear wall to define the room, is that it also reflects back the mids and highs as specular reflections, but that's relatively easy to deal with: band-width limited absorption with controlled reflection if the room is small, or a combination of that plus diffusion if the room is large enough to allow the use of diffusion (many home studios are not large enough, but people try anyway, then wonder why they can't get good acoustics... :) ).

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I have access to a Newell type studio here in Adelaide,
Are you certain it is a true Newell design? As in: "specifically designed by Newell himself"? Or is it just a copy-cat type room? Or maybe it's one that looks like a Newell design but is actually something else? It's hard to tell the difference, unless you have access to the original plans or construction photos. You can't tell just by looking, since what makes the design work is hidden by the room itself.

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The whole Newell NE thing is based on the assumption that my room is really a tad too small and I'm not very wealthy,
Then I'm a little confused! If you are on a tight budget with very limited space, then why would you choose an expensive design concept that requires a lot of space? The asymmetric outer-leaf boundary walls of a true NE design take up a lot of space, and the inner acoustics takes a lot of careful design to make it work. It looks easy when you read his books, but it's not so easy (or cheap) when you actually try to do it in practice. It works, yes, but you need a large space and a matching budget to make it work...

If you have a small space then an RFZ design would likely be better, since it does not require the wasted space of an asymmetric outer leaf, nor does it require complex inner treatment. Right now I'm working on the design for a really, really, REALLY small studio, of slightly more than 9m2 :shock: Yep: no errors in that number: it really is nine square meters. I'm doing it as an RFZ design with soffit-mounted speakers for many reasons, but mostly because it is so small. The soffits include treatment as well, to make the best possible use of space, and they are almost complete now. Recently the owner sent me an e-mail saying: "I finally got all the lower mini hangers in, and also the 703 in the top section. Wow! These ... are amazing! I have never put a bass trap in a room and had such a noticeable change!" He's pretty impressed by the results, it seems, and do bare in mind the minuscule scale of this room: to get the bass under control is a big deal in a small room. I can safely say that it would not have been possible to achieve that with an NE approach.

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but I'm totally open to your expertise in this area.
Here's an interesting thing you can do to help you decide: Take a look at magazines such as "Mix" and "Sound on Sound" for the last few years, at the articles they often run on high-end studios. Count how many of those are RFZ-style desgns, and how many are are true NE designs... :)

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Yep, and because there is 2 doors in corners, I assumed there was no room for treatment
Doors are a pain, yes, and they do get in the way of treatment, yes, but there are ways around that. There are methods for optimizing room treatment, even when things like doors and windows get in the way. Of course, if you can move the door (which usually isn't as hard or as scary as it sounds) then that's a better option.

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hence the dead zone in the end of the room idea,
That unbalances the room, since it basically takes it back to being like a LEDE room from the 70's nor 80's....

Yes, the rear does need to be dead... but only for lows, not for mids and highs. It needs to return ALL frequencies to the mix position as evenly as possible, delayed by at least 20 ms, and at a level at least 20 dB below the direct sound, and preferably diffuse, not specular. That was one of the issues with LEDE: it totally sucked the life out of the room, leaving it unbalanced, unnatural, and fatiguing.

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but now that I've realised I could just undo some work that I've done, I could gain 2 metres.
Excellent! If there's one basic rule that all studio designers can agree on, regardless of the design approach, it would be that "size matters".... Maximize your room volume. Get it to at least 47 m3, which is the minimum volume for good acoustics according to some studies. Maximize your floor area, so it is at least 20 m2, or 30m2 id you plan on doing multi-channel mixing (5.1, 7.1, etc.). And maximize room length, to get as much space as possible between your head and the rear wall. Those are the three "holy grail" parameters that everyone searches for. Whatever you can do to achieve those, will be good for your room.

I'm working with a customer right now in Europe, where his room could be fantastic if only he could take down some simple light-weight non-structural glass partitions at the back of the room, and add the space just beyond that to his room (about a meter deep)... but the boss won't let him do that, so he's stuck with a non-optimal room. He's a sad guy right now, but we'll make the best of it.

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I understand this.
Good! Because it can't be achieved if one end of the room is all reflective, and the other end is a giant "sound sucker" that kills the entire spectrum. If the rear end of the room soaks up all sound and does not return a low-level diffuse field, then it is physically impossible to achieve that. There's no other place that the diffuse reverberant field could come from, except the rear wall, and if you either eliminate the rear wall or make it overly absorptive, then there can be no diffuse reverberant field after the ITDG. And that's the key to having proper ambience in your room.

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I understand what you're saying, the whole building is concrete, so isolation should not be too hard really.
:thu:

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Problem is I started building the studio before I really understood what was required. Now I'm erring toward pulling out a wall and starting again.
:thu:

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87dBA was my comfortable listening level.
Assuming typical contemporary genres, that's pretty loud. Likely around 100 dBC, which is how you should be measuring it. "A" weighting does not take into account the low end: it starts rolling off at 1 kHz, and it is 26 dB down by the time it reaches 60 Hz. At 20 Hz, it is -45 dB. So if you set your meter to "A", it is not showing you the real intensity of the entire spectrum. "C" weighting is a much better approximation of how the human brain actually perceives loud sounds. Take a look at the Fletcher-Munson curves, or the derived equal-loudness curves to see why. "A" weighting is appropriate for measuring quite non-musical sounds, but "C" is what you need for loud music. I'd suggest that you check your levels again, using the "C" weighting and "Slow" response settings on your meter.

Quote:
my 'wall' is 350mm thick poured concrete. I can mount speakers to that without fear of vibration.
Are you SURE about that? What is damping that wall? Did you try tapping it gently with a hammer, and looking at the decay curve? Even better, get a friend to tap the wall towards one end, while you press your ear up against the other end... Can you hear the vibrations that you have now passed into the building structure? You have taken the air-borne sound produced by the speaker, and directly coupled it into the building. So it is now structure-borne sound, that will be potentially hear anywhere in the entire building... :)

Quote:
I can stand the baffle on 600x300mm concrete and mount the supporting struts to a 350mm concrete wall and still have no vibration issues that I can see.
Are you sure about that? :) Let's take a look at your SketchUp design, and see if it will achieve what you are hoping.

Quote:
I can hang a solid steel shelf per speaker
Steel is rather resonant... it rings very nicely when you tap it! Depending on the dimensions of the plate, it will have several resonant modes, and with a speaker sitting directly on it, all of those will be triggered. So basically, you want to sit your speaker on top of a drum head... :)

Quote:
Like a spiral staircase if you know what those treads look like..
Have you ever noticed how loud a steel spiral staircase is, as you run up it? :) It sort of rings and thumps loudly with each footfall...

Quote:
My speakers are passive at the moment, but I looked at Johns design for soffit and thought I'd manage air flow if I needed to.
It's not a matter of "if" you will need to! It's a basic requirement. And active/passive is pretty much irrelevant: Speaker drivers are extremely inefficient at converting electrical energy into acoustic energy, totally independent of the amp that is driving them. An amp might be pumping out 100 or 200 watts of electrical power, directly into the driver in order to produce 100 dB SPL, but that driver will only manage to convert that into about one watt of actual acoustic energy. And that's assuming the driver is very efficient! An inefficient driver will need even more power to produce one watt of acoustic power. But let's assume that you have a really efficient driver in a very well designed cabinet with an excellent impedance matching curved baffle. State of the art in speaker design. Let's assume that it can produce one watt of acoustic power from 100 watts of electrical power. So where did the other 99 watts go? :) Yup, you guess it: they ended up as heat. And since this is all happening inside the driver, the speaker itself will get hot (and need cooling) regardless of whether it is active or passive. An active speaker might need even MORE cooling if the power supply and amp are also inefficient, but the main culprit hear is the driver. Or rather, driverS: plural. There will be at least two of them, maybe more. Some tweeters might be more efficient than that (the ART, for example), but the woofer will typically not be efficient. And since the woofer needs to put out twice as much acoustic power as the tweeter in any case (due to the baffle step response issue, and the resulting 6 dB power imbalance), that's where most of the heat is going to be produced.

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I don't think they make it anymore!! I tried to find it as well! It's what I have anyway, it's super absorbent
I'm sure it is! It might even be "amazingly, fantastically, hyper-absorbent", but if you don't have the specs for it, you'll never know what the coefficient of absorption is for each frequency band, so you'll never know where you can use it, nor what it will do to your room. You don't even know what the gas flow resistivity is (MKS rayls), so you can't estimate how well it will perform for any given application.

I'd suggest that you contact the manufacturer, and ask for the spec sheet. If you can't get that for any reason, then I would not use it in your room.

Quote:
you mentioned plastering up the besser block wall with a heavy plaster to 'mass it up', but would 3 layers of cement sheet do the same at 9mm each?
Pretty much the same, but it won't seal the wall like plaster would, and how would you attach it?

Quote:
It would be MUCH easier for me to do as the access to flat ground outside
"outside"? Who said anything about outside? I'm talking about INSIDE your room. Plaster the inner leaf walls that you see around you as you stand inside the room. You need to do that anyway to seal the porous surface. You can't have a porous surface facing your wall cavity, as it changes the acoustic characteristics of the cavity itself.

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is difficult and mixing mud is hard work
Yep! So is building a studio! :) Or you could by the read-mixed plaster, that comes in a bucket: just open the bucket and slap it on!

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and plastering is highly skilled.
Only if you want a nice smooth, pretty finish. This does not matter, since it will be inside your wall cavity, and nobody will ever see it. You can do a really ugly job of plastering, and it does not matter. As long as it seals the wall and covers it to roughly the right depth, that's all that matters.

Quote:
Thanks again for your input
:thu:


Quote:
I'm having a red hot go at Sketchup. Bit of a learning curve,
It takes a bit of getting used to. It has it's quirks, for sure, but once you get past the basics, it's very, very powerful. The biggest key is to remember to always do a "make component" operation on very new bit of geometry that you create. Second key is to assign all similar geometry to separate layers in the "layers" window. Third key is to set up "scenes" in the "scenes" window, with useful sets of layers turned on or off, and useful camera locations. Once you get those down pat, the rest is easy.


- Stuart -

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