The No.1 Website for Pro Audio
 All  This Thread  Reviews  Gear Database  Gear for sale     Latest  Trending
New construction 2-ch listening room build questions
Old 24th July 2019
  #1
Here for the gear
 

New construction 2-ch listening room build questions

Hey all,

I'm a long time reader of this board - first time posting.

I'm in the middle of constructing a new dedicated building for 2-ch listening. We are putting in an Atmos system and projector for occasional use, but primarily designing the room for 2-ch listening.

The room dimensions are 21'2"L x 15' 9" W x 10' H. Concrete slab floor. Equipment room is outside of this room. Right now the building is framed and insulated with a continuous air/vapor barrier over the in wall insulation (eco-batt).

We have been doing initial speaker placement and acoustic design in Sketchup just to get a sense of how to work things in aesthetically. Initial planning has superchunks on front wall corners floor to ceiling, superchunks on top front wall at wall to ceiling and potentially back wall and corners, 2" panels at 1st and 2nd ref side walls, 4" ceiling cloud, a rug, and an acoustic curtain in front of a large window on the front wall (11'w x 7'h). We're anticipating diffusion on the back wall. Since the room isn't complete and there is no power on site we are unable to test things until further down the road (unless we run gear off generators). So these initial acoustic designs are just ballparks to get us started and I'll reach back out to the board as things progress.

The room is designed to be wood paneling interiors. We initially used a wood slatted design on all of the walls and ceiling with the thought of integrating the acoustic treatments by way of Binary Amplitude Diffusion or something similar. Important to note - we have a 2" "service" cavity on the ceiling and walls - basically battens that sit inside the air barrier. This service cavity contains our electric and the thought was that it could accommodate 2" panels at reflection points, and potentially covering them in slatted wood w random patterns per Andre's wonderful posts here. But without listening tests we're not committing to any acoustic treatments yet, just wanted to note the 2" service cavity and it's possible use to hide/integrate some absorption.

Anyways, my question at this point is just about sheetrock - as we weren't initially planning to rock the interior (and don't need to air seal the cavity of the room) and just put the slats directly on the battens . But as we were installing our 2" battens on walls and ceiling I realized that a slatted design would mean the wall insulation will be exposed to sound through the slatted design. I've been looking for information on the necessity of sheetrock in an acoustic environment and it seems as though all rooms I come across are rocked and then acoustic treatments are placed on top of the rock.

Finally, my questions:
1. First off, Is sheetrock necessary in a listening room? Ie. if the wood is installed tongue and groove w/o gaps is there any acoustic benefit to have rock behind it?

2. If the slatted design was done with gaps minimized in width - would that work without sheetrock behind it? If so what would be an acceptable maximum gap to board width ratio? ie if the board is 3" thick and the gaps were 1/4" that would be about 8% of the surface area exposed to the insulation behind it. Does this create an acoustic problem?

3. If sheetrock is recommended is there a minimum thickness? Provided we don't need the structural support in any way it would simply be for acoustic purposes and I suppose to protect the air barrier integrity.

4. Anything that I should be concerned or thinking about at this stage in construction? (besides the 11' window on the back wall ).

I've attached some pictures - the current room before battens installed, a rough render of a WIP design w slats (the slats in front of broadband absorbers are just temporary we'll be experimenting with listening tests to determine what if any slats can go in front of these to be effective). and a quick render of potential acoustic treatment before slats would go in.

Thanks for any help and guidance. Really looking forward to input from this community on my project!

Anthony
Attached Thumbnails
New construction 2-ch listening room build questions-img_0485-copy.jpg   New construction 2-ch listening room build questions-screenshot-2019-07-19-12.42.47-copy.jpg   New construction 2-ch listening room build questions-screenshot-2019-07-20-09.23.30-copy.jpg  
Old 24th July 2019
  #2
Lives for gear
 

Quote:
Anyways, my question at this point is just about sheetrock - as we weren't initially planning to rock the interior (and don't need to air seal the cavity of the room)
If that was your plan, then it would seem that you don't really need any isolation for your room: Implying there are not outside noises that could interfere with your listening experience, such as rain, wind, hail, thunder, cars, trucks, aircraft flying over, helicopters, sirens, radios, lawnmowers, dogs barking, and things like that? If you have no inner-leaf wall, then you have only the mass-law isolation of your outer leaf, which isn't going to be very much. If you live some place that has zero outside sounds that could annoy your listening, then that's fine. But most places where people build things are not silent outside.

Isolation works the other way too: if you have have loud sound inside the room and poor isolation, then that will get out and annoy anybody nearby.... how close are your neighbors?

So that's the first issue: if you do need isolation, then you need drywall on your inner leaf. And if you need the typical amounts of isolation that most people need for listening rooms, home theaters, and studios, you would not put the drywall on the same studs as the outer-leaf, but rather on a separate frame built just inside that one. In other words, you would end up with two frames: the ine you have now, exactly as it is with sheathing on the outside only, and your new inner-leaf frame that would have the drywall on only ONE side of of it. You could choose to put the drywall on the side facing the room, which is "conventional" construction, or you could choose to put the drywall on the other side of that frame, facing the cavity between that and the other leaf, in which case it is often called "inside out" construction, in which case you could indeed continue with your current plan of putting slats directly over the inner-leaf studs, and you could then tune your slats as needed to help treat the room, acoustically

As far as I know, this "inside-out" technique which is then also built as a "slot wall", was pioneered by the great John Sayers, a couple of decades ago, and he has then refined it considerably, and now uses it in most of the rooms he designs. His web-site is here, if you are interested: http://www.johnlsayers.com/ He also has a forum connected to that: http://www.johnlsayers.com/phpBB2/index.php where you can ask questions about how he does that, and how to tune it.

Quote:
1. First off, Is sheetrock necessary in a listening room?
It is necessary if you want isolation for the outside world, yes. If you need no isolation, you could skip that... but there are caveats that I'll cover below.

Quote:
Ie. if the wood is installed tongue and groove w/o gaps is there any acoustic benefit to have rock behind it?
I would not install slats in a listening room like that...

Quote:
2. If the slatted design was done with gaps minimized in width - would that work without sheetrock behind it?
A slat wall (also sometimes called a "slot wall") is a tuned acoustic device. The thickness of the slats, the width of the planks, the size of the gaps between them, the depth of the air gap behind them, and an insulation placed in the gap, all play a part. There are equations you can use to calculate what frequency each slat would be tuned to, and you can adjust all of the above factors to change the tuning to match what the room needs. Slat walls are not just for aesthetics: they are a critical part of the room acoustic treatment, as you can see on John Sayers designs. He uses different widths, gaps, depths and thicknesses to get the right results for each individual room.

Quote:
If so what would be an acceptable maximum gap to board width ratio? ie if the board is 3" thick and the gaps were 1/4" that would be about 8% of the surface area exposed to the insulation behind it. Does this create an acoustic problem?
Yes it does create a problem because all of your slats would be tuned to the exact same frequency, so the entire room would treat just that one thing, without doing much to all the other things that need treating! And if you choose the dimensions at random, it's very probable that you would end up treating a frequency that did not even need it at all!

Quote:
3. If sheetrock is recommended is there a minimum thickness?
Assuming we are talking about isolation, then yes. And you would need to calculate the thickness based on how much isolation you need. There are equations for that too.

Quote:
Provided we don't need the structural support in any way
Drywall is not structural. It is rather brittle, in fact, and you can break it with your bare hands.

Quote:
it would simply be for acoustic purposes and I suppose to protect the air barrier integrity.
If that sheeting visible in your images is an air barrier, then you have a problem: It's in the wrong place! That should probably be a vapor barrier, not an air barrier. That depends on climate, though. Your building should have a water barrier on the outside of the outer-leaf, and a vapor barrier on the inner-leaf, inside the wall cavity, and up against whichever surface is warmer in winter. Usually, that means it goes against the inner-leaf. But find out out where to put water barriers, air barriers, and vapor barriers is rather complex, so you should check your local building code to find out what is required in your area.

Quote:
4. Anything that I should be concerned or thinking about at this stage in construction? (besides the 11' window on the back wall ).
I think you mean the FRONT wall? The back wall would be the one behind your back as you sit or stand in the room facing towards the speakers and video screen. The front wall is the one in front of you.

But anyway, yes, that window is a big issue, mainly from the point of view of isolation, and also from the point of view of acoustic response inside the room.

Quote:
the slats in front of broadband absorbers
Ummmm... if you have slat COVERING your broadband absorbers, then they are not broadband absorbers any more! They will only absorb whatever frequencies are NOT reflected off the slats, and happen to make it through them...

Quote:
we'll be experimenting with listening tests to determine what if any slats can go in front of these to be effective).
Hopefully you have a few dozen months set aside for that! It's going to take a hell of a long time to figure out how to tune the room acoustic response by trial and error... it would be much better to simply design the walls and ceiling correctly, to produce the acoustic response that you want.

Good room acoustic response happens by design, not by accident or randomly changing things. Design the room from the beginning with the desired response, then build it, then do the final tweaking to get the tuning perfect.

Quote:
and a quick render of potential Acoustic Treatment before slats would go in.
I don't see any bass trapping in there, nor diffusion, nor sufficient / suitable treatment overall....

- Stuart -
Old 24th July 2019
  #3
Here for the gear
 

Thanks for your thoughtful reply Stuart.

Quote:
Originally Posted by Soundman2020 View Post
If that was your plan, then it would seem that you don't really need any isolation for your room: Implying there are not outside noises that could interfere with your listening experience, such as rain, wind, hail, thunder, cars, trucks, aircraft flying over, helicopters, sirens, radios, lawnmowers, dogs barking, and things like that?
Yes sorry i did not mention isolation as indeed we aren't too concerned about that. this is a standalone structure in the middle of the desert - looking out onto Joshua Tree National Park. Closest neighbor is .5 miles away in any direction. That said we do have considerable wind which could present a noise issue I suppose and I completely overlooked drywall used as a source of sound isolation from wind noise.

This building is all exterior walls so the enclosure is separated from any other rooms that would present noise issues. The building exterior is sheathed in 1/2" struc 1 plywood, wrapped in a continuous 2" of eps rigid insulation (insulfoam). There is a rain screen (air gap) and then wood siding. The studs are 2x6 filled w fiberglass insulation. Is there a way to calculate the STC of the wall enclosure with and without sheetrock? I'm wondering how much of a difference a layer is actually going to make. But it does seem prudent to install a thin layer of drywall.

Quote:
Originally Posted by Soundman2020 View Post
Yes it does create a problem because all of your slats would be tuned to the exact same frequency, so the entire room would treat just that one thing, without doing much to all the other things that need treating! And if you choose the dimensions at random, it's very probable that you would end up treating a frequency that did not even need it at all!
The slats are not supposed to be acoustic treatment. It is an aesthetic choice. Ie. where one would traditionally put drywall and absorbers on top of that we will have slatted wood.

Quote:
Originally Posted by Soundman2020 View Post
Assuming we are talking about isolation, then yes. And you would need to calculate the thickness based on how much isolation you need. There are equations for that too.
Do you know what this equation is or point me to a place to calculate? I can't seem to find anything that factors in wall construction without a layer of drywall first. They all assume 1/2" of drywall as standard.

Quote:
Originally Posted by Soundman2020 View Post
I would not install slats in a listening room like that...
Hm. reasoning for this? What would a surface wall be constructed with if a wood interior is preferred? Not talking about acoustic treated areas.

Quote:
Originally Posted by Soundman2020 View Post
If that sheeting visible in your images is an air barrier, then you have a problem: It's in the wrong place!
Ha, this isn't the place to debate 'building science' but re: building envelope. there is continuous exterior weather and air barrier and interior air and vapor barrier on this building to achieve passive house standard. these are 'smart' membranes meaning they don't let air through but will allow vapor to permeate through to the inside and outside if moisture (condensation) does make it's way into the cavity for any reason. These details are not typical for construction in the US but very common in European standards.

This does lead to another question I have, however. In a tight building envelope is there anything needed to consider in terms of speaker/sound moving air? these structures have 24/7 ERV - fresh air is continuously supplied to main space while humid, stale air is continuously exhausted to the exterior. This is essentially making up for air that would traditionally make it's way into a home through leaks in a building's envelope - ie windows, doors, improper wall sealing, etc.

Quote:
Originally Posted by Soundman2020 View Post
I think you mean the FRONT wall? The back wall would be the one behind your back as you sit or stand in the room facing towards the speakers and video screen. The front wall is the one in front of you.

But anyway, yes, that window is a big issue, mainly from the point of view of isolation, and also from the point of view of acoustic response inside the room.
Yup i do mean the FRONT wall.

Again, not worried about isolation. However, for acoustic response of the room we were anticipating installing an acoustic absorbing curtain in front of this window for theater use, but assuming it will lead to the room sounding too dead for 2-ch listening. I saw one design with movable diffusor doors that could cover a front wall window. Any thoughts on treatment for this wall?

Quote:
Originally Posted by Soundman2020 View Post
Ummmm... if you have slat COVERING your broadband absorbers, then they are not broadband absorbers any more! They will only absorb whatever frequencies are NOT reflected off the slats, and happen to make it through them...
I guess I wasn't clear here - the 2" insulation (knauf 6lb or Roxul 80) could go in the service channel at the points of 1st and 2nd reflection on side walls. These would not have slats in front of them, but potentially some limited slats to integrate them into the design. The 4" thick ceiling cloud would sit below the ceiling with a 4" gap. Wouldn't those be defined as broadband absorption?

The superchunks in corners would be constructed hidden by wood slats - either in random or 345 pattern - with the goal of slight scattering of mids and highs and trapping low end.

Additional absorption and diffusion would be placed per listening tests and room analysis software.

Quote:
Originally Posted by Soundman2020 View Post
I don't see any bass trapping in there, nor diffusion, nor sufficient / suitable treatment overall....
The corners are 24x24 triangular superchunks floor to ceiling for bass trapping. Knauf 3lb or similar. Additional bass trapping would be worked into ceiling to wall transitions as necessary. Any thoughts on how much additional trapping I should anticipate in this room?

1st and 2nd reflection points are planned with 2" knauf 6lb for now. Can be bumped up to 4" or an air gap created if necessary. Ceiling cloud is 4" of knauf 6lb with a 4" air gap. Diffusion is on rear wall. And slight diffusion (scattering really) on Front wall in corners covering the superchunks. What further treatment overall would you suggest to make this room 'suitable' at this stage? I had anticipated using this as a base layer and building up from there - based on all of the acoustic advice I've read and been given. But if I am missing something critical by all means tell me what I'm overlooking!

Thank you again.
Anthony
Old 25th July 2019
  #4
Lives for gear
 

Quote:
The building exterior is sheathed in 1/2" struc 1 plywood, wrapped in a continuous 2" of eps rigid insulation (insulfoam). There is a rain screen (air gap) and then wood siding. The studs are 2x6 filled w fiberglass insulation. Is there a way to calculate the STC of the wall enclosure with and without sheetrock? I'm wondering how much of a difference a layer is actually going to make. But it does seem prudent to install a thin layer of drywall.
There certainly is a way to calculate the estimated isolation. Actually, there are several ways, depending on how the studio is built. If you just have a single-leaf wall, like you do now (your wall is a bit more than single leaf, but it will act mostly like single-leaf), then you are subject to a set of equations known as "mass law". And those equations are not very friendly for isolation, unfortunately. In simple terms, what mass law says basically is that, under ideal conditions, every time you double the mass of the wall, you get a miserly increase of 6 dB in isolation. That's under ideal conditions, assuming perfect mass, perfect construction, etc. In the real world, it's more like 4 to 5 dB for each mass doubling. Considering that you need about 10dB to subjectively say that the sound level went down by half, that implies that you would need to double the mass, then double it AGAIN to reduce the subjective sound level by half. And to get it down to a quarter of what it was, you would need to double yet again AND yet again.... You can see that trying to get good isolation from a single-leaf wall is not really a good option. You get nowhere, slowly.

To put all of this in perspective for you, a typical ordinary stud wall in a house, with 2x4 studs having 1/2" drywall on each side, is going to get you maybe 30 dB of isolation, with luck. On a good day. With the sun shining brightly. And a gentle breeze blowing. Probably a bit less under typical conditions. You already know that such a wall is pretty lousy at isolating: you can hear people talking through that, and music comes through as though the wall wasn't even there. At the other end of the scale, arguably the best isolated recording studio on this planet is Galaxy Studios in Belgium: they get around 100 dB isolation. In subjective terms, they are about 128 times quieter than a typical house wall (7 steps of 10 dB). You could yell and scream your head off in there, and smash things on the floor, and play the drums louder than Phil Collins on steroids, and nobody would hear you at all. You could play an entire Grateful Dead concert in there, together with Pink Floyd at the same time, at maximum power, and STILL not be heard outside as more than a vague whisper... So those are the two extremes. Typically, home recording studios amd good home theaters and audiophile rooms get something in between, around 50 to 60 dB of isolation. Your needs probably lie somewhere in that range, but the only way to be sure, is to so some measuring of levels, with a decent quality hand-held sound level meter.

So, the big question here is: How does your single-leaf wall stack up against that "typical house wall" that I mentioned? Well, making a lot of assumptions, we can use the simplest form of the Mass Law equation to figure that out. All we need to know is the "surface density" of your wall. In other words, if we could cut out one square meter of your wall and weight it, how much would that weigh? Fortunately you don't need to actually cut out chunks of your wall! We can estimate, based on the typical characteristics of those building materials:

"sheathed in 1/2" struc 1 plywood,". Plywood has an absolute density of somewhere around 560 kg/m3, so sheets 1/2" thick (roughly 12mm) will have a surface density of around 7 kg/m2 (I'm only estimating very roughly and rounding lots, to keep the math simple. There's no need to be accurate for this estimate. You'll see why...)

"2" of eps rigid insulation" The mass of that is negligible here, but lets' call it 1 kg/m2, to be generous.

"There is a rain screen (air gap) and then wood siding. " You didn't say how thick or what type of wood, but being generous let's estimate 1/2" thick cedar. That would work out to a density of around 5 kg/m2.

So, your total surface density is 7 + 1 + 5 = 13 kg/m2.

Now plug that into the empirical mass-law equation, which goes like this:

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

Where: M = Surface density in kg/m2

So, we have

= 14.5 log (13 * 0.205) + 23 dB
= 14.5 log (2.6) + 23 dB
= 6 + 23
= 29 dB

So your wall is acting sort of similar to a typical lousy house wall, in terms of isolation. No quite as good, but close.

Now for the fun: Let's assume that you only need 50 dB of isolation, and you already have 30. So, if you double the mass of your wall from 13 kg/m2 to 26 kg/m2, you would get an increase of 5 dB, and you'd be at 35 dB. Double it again (to 54 kg/m2), and you get 40 dB. Double it again (108 kg/m2) and you get 45 dB. And double it one more time (216 kg/m2), then you'd get your 50 dB isolation. Since you increased your isolation by 20 dB, subjective things would be about 1/4 as loud as the are now.

Now, with your jaw on the floor, you realize that you would have to increase the mass on your wall SIXTEEN TIMES what it is now! In other words, 16 layers of 1/2" drywall, 16 layers of foam, and 16 layers of siding....

OK, hopefully I've now convinced you that just adding more mass to your existing wall is not the way to go... As I said, mass law is not your friend. Single-leaf is not your friend.

Fortunately, there's a better way. A MUCH better way. As I mentioned yesterday, you could build a proper 2-leaf wall by simply putting up another set of framing inside your current framing (walls and ceiling, resting on the same floor), and putting some sheathing on that. As long as the two frames don't touch each other anywhere (not even a single nail), you can get much better isolation with much lower mass. You completely leave "mass law" behind, and move into a whole different ball-game when you go to a fully decoupled 2-leaf isolation system. Adding that second leaf does far more than what you'd think. Logically, you'd expect it to be twice as good, but it's actually way better than twice as good. You could probably get your 50 dB of isolation by just putting 2 layers of 5/8" drywall on your inner-leaf frame, along with suitable insulation in the cavity (instead of 16 layers of drywall, plus 16 layers of foam, plus 16 layers of siding...). The reasons why it is so much better are a bit complex, and I won't bore you with those, but this is the way most studios are built, because: it works!

So this decoupled 2-leaf system is a much, much better option than what you have now.

Excuse my long waffle about isolation, but it's important to understand what your options are here. And hey, you DID ask if it could be calculated!

Quote:
I'm wondering how much of a difference a layer is actually going to make. But it does seem prudent to install a thin layer of drywall.
I think I answers that above... But don't guess at how much drywall you'd need on your second frame: calculate! Or look it up in the tables and charts about isolation structures.

I'm sure you are thinking: "But surely I could just put the drywall on the existing stud framing to get 2 leaf! Much easier." Welll... nope! You can't! Because that framing would "couple" the drywall on the inside to the sheathing on the outside, making them act together as one unit, so you would basically be back to mass law again. You need the second frame to "decouple" the two leaves, so they are not mechanically connected to each other, and can act independently.

Quote:
The slats are not supposed to be Acoustic Treatment. It is an aesthetic choice.
It doesn't matter what they are "supposed" to be! The slats and the sound waves really don't care what you think their purpose should be: rather, they will just react to the physics of the situation, and they WILL act acoustically. They will simply act in accordance with the surfaces they meet. Even if you hang big signs on the walls, saying "Dear Sound Waves: WARNING! These slats are aesthetic, not acoustic! Do not react acoustically!", that still wont help: Sound waves can't read, and they are really stubborn basstttards anyway, always doing just what they want, so you'd be out of luck: they will still react to the slats acoustically. Sorry!

Quote:
here one would traditionally put drywall and absorbers on top of that we will have slatted wood.
... and the sound waves would love that! Thy will happily behave as sound waves always do when they run into slats... (Even if you turn the lights off, so they can't SEE the slats...)

Quote:
Do you know what this equation is or point me to a place to calculate? I can't seem to find anything that factors in wall construction without a layer of drywall first. They all assume 1/2" of drywall as standard.
You already have the equation for "mass law", which I gave you above, so that's a start. But that's the simplified empirical equation that does not consider frequency. From here on we need to move to the slightly more complex version, which does consider frequency. Because two-leaf walls are more complex, and frequency is a more complicated factor here. And the equations are more complex, too. In fact, there's a set of equations for this, and each equation calculates part of the audio spectrum, based on frequency. Because a 2-leaf wall is resonant in ways that a single-leaf wall is not, and you have to take that into account.

Here's the full set of equations for roughly estimating the isolation in each of the three frequency ranges:

First, you have to think of the wall as being a pair of single leaf barriers, so you need Mass Law equation again:

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

Where: M = Surface density in kg/m2

Now you need to calculate the above for EACH leaf separately (call the results "R1" and "R2").

Next, you need to forget that it is a pair of single leaf walls, and start thinking of it as a resonant two-leaf wall, so you need to know the resonant frequency of that 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 or lbs/ft2)
m2 mass of second leaf (kg/m^2 or lbs/ft2)
d=depth of cavity (m or ft)

(C=43 for imperial empty, 1897 for metric)

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)/2 + 20log(f * d) - 29 ...[for the region where f0 < f < f1]
R = R1 + R2 + 6 ...[for the region where f > f1]

Where:
m1 and m2 are the surface densities of leaf 1 and leaf 2, respectively
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.

So you will end up with three numbers that estimate the isolation for each of the three regions. You can plot those on a graph if you want, to get a better idea of how the wall will isolate. That will give you a very, very rough approximation of the "transmission loss" curve for the wall. It is possible to calculate a much more accurate and detailed TL curve, but the math gets complicated...

Quote:
Not talking about acoustic treated areas.
Once again, there's no such thing! EVERY surface in your room is an acoustic area! The sound waves won't stay away from certain surfaces just because you don't want them there... Sound is a 3D field that fills the entire room, and interacts with every surface around the room, and every object in the room. The sum total of all that is the "acoustic response" of the room. There's no such thing as "acoustic areas" and "non-acoustic areas. All areas are acoustic, like it or not. And the sound will get to all of them, and react to all of them.

Quote:
In a tight building envelope is there anything needed to consider in terms of speaker/sound moving air? these structures have 24/7 ERV - fresh air is continuously supplied to main space while humid, stale air is continuously exhausted to the exterior. This is essentially making up for air that would traditionally make it's way into a home through leaks in a building's envelope - ie windows, doors, improper wall sealing, etc.
You mean exactly like a typical studio, then? That's exactly the way studio HVAC systems are done, for a very simple reason: each of the two leaves MUST be sealed totally air-tight. Because the equations above depend on that. The air trapped in the cavity between the leaves must be totally trapped in there, unable to leak in either direction. So it's good that you already have that implemented on the outer leaf: you inly need to take care that the inner-leaf is sealed airtight as well.

Quote:
However, for acoustic response of the room we were anticipating installing an acoustic absorbing curtain in front of this window for theater use, but assuming it will lead to the room sounding too dead for 2-ch listening.
Curtains are actually pretty lousy treatment for rooms. Curtains do a decent job of absorbing high frequencies, a vague halfhearted job of absorbing mid-range frequencies, and no job at all of absorbing lows. In most rooms, that's exactly backwards from what you need. Small rooms need a LOT of absorption in the lows (the smaller the room, the more bass-trapping it need), some in the mids, and little to none in the highs. Your room is large enough that you won't need crazy truck-load tons of low-end absorption, but you will still need a fair amount. Curtains will just make the room sound dull, muddy, and boomy, all at the same time.

Quote:
I guess I wasn't clear here - the 2" insulation (knauf 6lb or Roxul 80) could go in the service channel at the points of 1st and 2nd reflection on side walls. These would not have slats in front of them, but potentially some limited slats to integrate them into the design. The 4" thick ceiling cloud would sit below the ceiling with a 4" gap. Wouldn't those be defined as broadband absorption?
2" is better than nothing, but not much at all for first reflection points. The general recommendation for that is 6", and certainly no less that 4".

Now, you did say that this is mostly just a stereo listening room, but it seems rather large for just one person, so I'm assuming that it is for groups of people? If so, then you have SEVERAL first refection points in different locations: one set for each person. There's a lot of planning in figuring that out. It's not as simple as just slapping up a few absorption panels on the wall, apart way between the speakers and the chairs....

Quote:
Additional absorption and diffusion would be placed per listening tests and room analysis software.
You can save yourself a lot of time in those tests by first designing the room to get the response you want, rather than trying to get that afterwards by trial and error! Yes, you'll still need to do some final tweaking with ears and REW, but a hell of a lot less than if you don't design the acoustic response completely.

You might think you are doing that with your superchunks and absorbers, but you aren't. There's a lot more to it than that. For example: What is your target decay time? What is your planned early reflection time? How much will you allow that to vary between frequency bands? How will you ensure even coverage of the seating area, especially for the bass? Do you want the room to sound natural, or extra wide (in relation to the sound from the speakers, of course)? How many chairs will there be? What is the absorption profile of each of chair? Etc. Those are all things you should be considering, and building in to the basic acoustic design of the room.

Quote:
The corners are 24x24 triangular superchunks floor to ceiling for Bass trapping.
Rather small for a room that size. That's not going to get all of your low end under control.

Quote:
Additional Bass trapping would be worked into ceiling to wall transitions as necessary. Any thoughts on how much additional trapping I should anticipate in this room?
That depends on the numbers I mentioned above! "What is your target decay time? What is your planned early reflection time? How much will you allow that to vary between frequency bands?" Until you define that, you can't know how much absorption you will need in general, nor specifically based on frequencies, nor where to put it.

Quote:
Can be bumped up to 4" or an air gap created if necessary.
The air gap doesn't do anything useful, unless you move the panel out by the same amount. Thus, a 4" thick panel absorbs roughly the same frequency ranges as a 2" panel over a 2" air gap... but it does it more effectively.

Quote:
Ceiling cloud is 4" of knauf 6lb with a 4" air gap.
Where will that be hung, in relation to the speakers and seating area? What angle? Is it hard-backed, or not? Is one cloud going to be enough, assuming multiple seats? Why are you going with knauf 6lb for that, when the angles of incidence will be rather shallow? Have you checked if maybe a lighter, less dense insulation would be more effective? What frequency range are you expecting will need the most treatment up there?
Quote:
Diffusion is on rear wall.
Why? Tuned to what frequency range? Why that range and not a different one? How big is that diffuser, and what type is it? What that big, and why that type? How far is it away from the seating area? Is that far enough away to ensure that the ears of the listeners won't be in the login area caused by the diffuser, given the type of diffuser and the tuned range?

Quote:
What further treatment overall would you suggest to make this room 'suitable' at this stage? I had anticipated using this as a base layer and building up from there - based on all of the acoustic advice I've read and been given. But if I am missing something critical by all means tell me what I'm overlooking!
See above...

I guess the basic question here (in addition to how much isolation you need), is: how good do you want the room to be? Is this just sort of a nice place to listen to a bit of background music while chatting with friends? Or is it more of a serious audiophile type room, where you really want it to be very good, so you can hear every last minute detail of every last instrument? Without knowing that, it's really not possible to say what level of acoustic treatment you would need. If it's just for background music while a bunch of friends are sitting around pizza and beer, chatting, without really being involved in the music at all, then by all means do what you are proposing: throw up some curtains, a few panels here and there, slats without caring about tuning, any old chair in any old place, etc. No problem. It will work out fine for that. But if this is for very serious extreme critical listening, then I haven't even begun to talk about all the stuff you'd need to do... I've just covered the basics with broad brush strokes. So if you cold clarify the purpose and intention of the room, that would help. However, give the very large investment for putting up an entire building whose sole purpose is ti listen to music, I'm guessing that this is for the high end of the scale: serious critical listening.



- Stuart -
Old 4 weeks ago
  #5
Lives for gear
 
Starlight's Avatar
 

Quote:
Originally Posted by Soundman2020 View Post

Here's the full set of equations for roughly estimating the isolation in each of the three frequency ranges:

First, you have to think of the wall as being a pair of single leaf barriers, so you need Mass Law equation again:

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

Where: M = Surface density in kg/m2

Now you need to calculate the above for EACH leaf separately (call the results "R1" and "R2").

Next, you need to forget that it is a pair of single leaf walls, and start thinking of it as a resonant two-leaf wall, so you need to know the resonant frequency of that 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 or lbs/ft2)
m2 mass of second leaf (kg/m^2 or lbs/ft2)
d=depth of cavity (m or ft)

(C=43 for imperial empty, 1897 for metric)

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)/2 + 20log(f * d) - 29 ...[for the region where f0 < f < f1]
R = R1 + R2 + 6 ...[for the region where f > f1]

Where:
m1 and m2 are the surface densities of leaf 1 and leaf 2, respectively
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.
Nothing complex but what a lot of time this fascinating topic can eat up!

What is the aim of the f0? To be different to any of the modes? For example, if I have two lowest modes of 1-0-0 at 29Hz and 0-1-0 at 38Hz, should my aim be to get the f0 below 29Hz or is between them at 33 or 34Hz alright? Or, should the f0 be below audible frequencies, let's say below 10Hz?
Old 4 weeks ago
  #6
Gear Addict
 

Quote:
Originally Posted by Starlight View Post
Nothing complex but what a lot of time this fascinating topic can eat up!

What is the aim of the f0? To be different to any of the modes? For example, if I have two lowest modes of 1-0-0 at 29Hz and 0-1-0 at 38Hz, should my aim be to get the f0 below 29Hz or is between them at 33 or 34Hz alright? Or, should the f0 be below audible frequencies, let's say below 10Hz?
Fo or fs is the resonance frequency of the construction.
At this frequency the construction is theoretically not damped and will move very easely when exited by sound with this frequency so isolation is here minimal.
Isolation starts at the sqrt of 2 x this fs.
So trying to get fs as low as possible will provide best isolation.

It has in principle nothing to do with modes, although if you have a flimsy drywall construction with a fs that is by accident tuned at a mode you will have mode cancelation in the room (nice) but a problem with isolation (bad).
Using tuned membrane absorbers to tame modes can cause severe ptoblems regarding sound isolation.
Old 5 days ago
  #7
Lives for gear
Quote:
Originally Posted by bert stoltenborg View Post
Using tuned membrane absorbers to tame modes can cause severe ptoblems regarding sound isolation.
Because this way, it will act as a triple-leaf system (assuming a double leaf system was already there for soundproofing)?
Post Reply

Welcome to the Gearslutz Pro Audio Community!

Registration benefits include:
  • The ability to reply to and create new discussions
  • Access to members-only giveaways & competitions
  • Interact with VIP industry experts in our guest Q&As
  • Access to members-only sub forum discussions
  • Access to members-only Chat Room
  • Get INSTANT ACCESS to the world's best private pro audio Classifieds for only USD $20/year
  • Promote your eBay auctions and Reverb.com listings for free
  • Remove this message!
You need an account to post a reply. Create a username and password below and an account will be created and your post entered.


 
 
Slide to join now Processing…
Thread Tools
Search this Thread
Search this Thread:

Advanced Search
Forum Jump
Forum Jump