John Sayers' Recording Studio Design Forum Archive

The more I read, the more I get confused. I have read Rod Gervais' 'Build it Like the Pros' book, which has some very useful info, but I am still unsure as to the best strategy.

I am converting my garage into a small home cinema. It isn't a big space, only 2.75 x 5m, but I am going to construct a room within a room. My biggest concern is trying to keep as much sound from escaping to surrounding neighbours etc. as I do live in a town house with other houses close by, so I need to be conscious of this.

My plan was to have 100mm stud walls, with about 10-20mm air gap from the brickwork, with new ceiling joists build on top of these walls. This fully decouples me from the surrounding brickwork. On to these new walls and ceiling I would have x2 layers of plasterboard, with either Green Glue or TecSound in-between. Acoustic insulation will also be added of course.

However, I have been advised by a company I am buying supplies from that the IsoMax resilient clip/channel system would be preferable, but in order to utilise that I'd need to drop to a 50mm stud as I'd lose too much room width if I stuck with the 100mm. I'm certainly aware they have a vested interest in selling me their product, but they present a good argument from the vibration point of view and the added benefit the system offers in that respect.

That said, I cannot accurately determine if this is correct advice, and even if it is, whether a 50mm stud assembly all round will be strong enough to support my ceiling joists and the weight that will be going up there? If not, then it rules out this idea anyway.

Based on the advice in Rod's book, a double wall would be the best solution... again though, the overall wall thickness is an issue, but if I had a 10mm gap, then a 50mm stud, then another 10mm gap, and a second 50mm stud wall, covered in the plasterboard, that wouldn't be too bad. Thicker than the other solutions, but if it's going to be the most effective solution, maybe that's the way to go?

Any advice would be much appreciated as I'm really stuck. Thanks.

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My biggest concern is trying to keep as much sound from escaping to surrounding neighbours etc. as I do live in a town house with other houses close by, so I need to be conscious of this.

You really should define a number: how many decibels of isolation do you need? If you don't know what that number is, then it's impossible to figure out what building materials or techniques you will need.

My plan was to have 100mm stud walls, with about 10-20mm air gap from the brickwork, with new ceiling joists build on top of these walls. This fully decouples me from the surrounding brickwork.

Right!

On to these new walls and ceiling I would have x2 layers of plasterboard, with either Green Glue or TecSound in-between.

Those are two entirely different products, with very, very different purposes. Not comparable at all. Choosing between them is sort of like deciding if you prefer a fish or a bicycle...

However, I have been advised by a company I am buying supplies from that the IsoMax resilient clip/channel system would be preferable,

You should probably look for a different supplier then! What they are telling you is totally wrong. They are trying to sell you stuff that you do not need! Apparently, they are either ignorant, or dishonest. Either way, that's bad for you. If they are ignorant, and just don't understand how isolation works, then any advice they give you is suspect. And if they actually DO know how it works but are recommending this anyway, then it seems they just want your money and don't actually care about giving you good advice...

Here's the truth: Yes, IsoMax resilient clips plus hat channel (or any other similar product) will increase isolation on a NORMAL wall that has sheathing on both sides, but it will NOT do anything to improve a wall that is already decoupled with sheathing on only one side! All that the clips do, is to decouple the sheathing from the framing. Period. That's it. But if your framing is ALREADY decoupled, then decoupling it again serves no purpose at all (except to make the supplier richer, and you poorer...). The advice they are giving you is like saying that if you want to get really wet, then the best way to do that is to get completely submerged in a swimming pool, but also take hose pipe with you, so you can get even wetter.... IF you are already wet all over, then the hose will not make you any wetter! If your sheathing is already decoupled, then decoupling it again won't make it decouple any better!

It is also wrong to say that using clips+hat channel is BETTER than plain decoupling: Many studies have been done on this. For example, Google the paper "NRCC-44692", titled "A Simple model of the sound insulation of gypsumboard on resilient supports", and take a look at that. You'll find that this type of isolation is limited to a gain of about 15 dB in isolation, as compared to the same wall with no decoupling. That's a good gain, yes, but pales in comparison to what you can achieve by decoupling the entire frame. Here's te actual conclusion fron that report (last page): "The maximum increase in transmission loss due to the addition of resilient channels is about 15 dB and only occurs for cavity depths greater than about 75 mm where the cavities are filled with sound absorbing material.". So your friends at the supplier are just plain wrong.

OK, so that report is about RC, but hat channel on clips is similar. Not a huge difference.

but they present a good argument from the vibration point of view and the added benefit the system offers in that respect.

And they would be wrong, no matter how convincing their argument is. Actual tests by acousticians in proper acoustic laboratories with the best equipment, prove them wrong.

That said, I cannot accurately determine if this is correct advice, and even if it is, whether a 50mm

It isn't, and not the conclusion that you need at least 75mm just to get that 15 dB improvement....

whether a 50mm stud assembly all round will be strong enough to support my ceiling joists and the weight that will be going up there?

Use a span table, or span calculator, to find that out, roughly, but the best bet is to hire a structural engineer to check out exactly what you are doing, and sign off on it. He's the ONLY person qualified to tell you that.

Based on the advice in Rod's book, a double wall would be the best solution... again though, the overall wall thickness is an issue, but if I had a 10mm gap, then a 50mm stud, then another 10mm gap, and a second 50mm stud wall, covered in the plasterboard, that wouldn't be too bad. Thicker than the other solutions, but if it's going to be the most effective solution, maybe that's the way to go?

I don't understand what you are saying: you are already building a double-wall system (full-decoupled 2-leaf MSM isolation system): In what way is that different from what Rod describes?


- Stuart -

Thank you for your detailed response.

Soundman2020 wrote:You really should define a number: how many decibels of isolation do you need? If you don't know what that number is, then it's impossible to figure out what building materials or techniques you will need.

I am not sure how to answer that. Is there a typical 'range' for an 'average' small cinema set-up utilising a 5.1.2 speaker set-up? I am not one for blaring out at max volume, that's all I can say.

Those are two entirely different products, with very, very different purposes. Not comparable at all. Choosing between them is sort of like deciding if you prefer a fish or a bicycle...

I have heard many arguments for Green Glue over TecSound (I'm aware the former is favoured by many on this forum), but I wasn't aware they weren't even comparable? Can you elaborate?

Here's the truth: Yes, IsoMax resilient clips plus hat channel (or any other similar product) will increase isolation on a NORMAL wall that has sheathing on both sides, but it will NOT do anything to improve a wall that is already decoupled with sheathing on only one side! All that the clips do, is to decouple the sheathing from the framing. Period. That's it. But if your framing is ALREADY decoupled, then decoupling it again serves no purpose at all (except to make the supplier richer, and you poorer...). The advice they are giving you is like saying that if you want to get really wet, then the best way to do that is to get completely submerged in a swimming pool, but also take hose pipe with you, so you can get even wetter.... IF you are already wet all over, then the hose will not make you any wetter! If your sheathing is already decoupled, then decoupling it again won't make it decouple any better!

It is also wrong to say that using clips+hat channel is BETTER than plain decoupling: Many studies have been done on this. For example, Google the paper "NRCC-44692", titled "A Simple model of the sound insulation of gypsumboard on resilient supports", and take a look at that. You'll find that this type of isolation is limited to a gain of about 15 dB in isolation, as compared to the same wall with no decoupling. That's a good gain, yes, but pales in comparison to what you can achieve by decoupling the entire frame. Here's te actual conclusion fron that report (last page): "The maximum increase in transmission loss due to the addition of resilient channels is about 15 dB and only occurs for cavity depths greater than about 75 mm where the cavities are filled with sound absorbing material.". So your friends at the supplier are just plain wrong.

Correct me if I'm wrong but that test appears to be testing the channels directly fitted to studs? The IsoMax channel system doesn't do that... there is no DIRECT contact with the joists, the channel is contained within the rubber clip. The Genie Clip system is similar, and the figures put forward by IsoMax and Genie Clip all present a convincing picture, and say they outperform standard resilient bar by up to 7dB, and exclaim to be the ultimate sound proofing solution (which I know isn't true). Have third party tests been done on IsoMax or Genie Clip specifically to disprove those claims? Regardless, I'm aware this doesn't change your previous point about the single sheathing, so even though I'm sure IsoMax performs better than standard resilient channel, from what you're saying that would ONLY come in to effect if you had sheathing both sides? In my specific situation, it won't help at all?

the best bet is to hire a structural engineer to check out exactly what you are doing, and sign off on it. He's the ONLY person qualified to tell you that.

Well it's a moot point if I don't actually go with the IsoMax system, as I would go with my original plan of 100mm stud. The only reason I was looking at 50mm was due to the IsoMax.

I don't understand what you are saying: you are already building a double-wall system (full-decoupled 2-leaf MSM isolation system): In what way is that different from what Rod describes?

Sorry, yes you're right... I'm confusing myself and thinking this is two walls within the same room.

Bottom line and the only real question I have is... am I better to go with 100mm stud decoupled from the wall, or 50mm stud with IsoMax? The answer to that seems obvious actually, but is there ANY reason you would use IsoMax in my scenario, or would it always have an inferior result?

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I have tried three times already: I will give this just one more try, then I'm giving up:

READ THE forum rules for posting (click here). You are still missing something!

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I am not sure how to answer that. Is there a typical 'range' for an 'average' small cinema set-up utilising a 5.1.2 speaker set-up? I am not one for blaring out at max volume, that's all I can say.

Get a sound level meter. Measure the actual level. That's how loud you are. Get a copy of your local noise regulations. That's how quiet you have to be. Do the math.

I have heard many arguments for Green Glue over TecSound (I'm aware the former is favoured by many on this forum), but I wasn't aware they weren't even comparable? Can you elaborate?

GG is a CLD (Constrained Layer Damping) compound. It does not add mass to the wall. It works by damping the bending waves in the sheathing. If you don't know what bending waves are, then you could google that. TecSound is flexible mass, similar to MLV in concept. It is not a CLD. Two entirely different principles. TecSound also provides no usable acoustic data on their products, so it is impossible to say how well they work. I have no doubt THAT the work, but without independent test reports from a reputable lab, there's no way of knowing of the results are fantastic, mediocre, or disappointing, nor way way to judge value for money. On the other hand GG provides mountains of data on their products, from many sources.

Correct me if I'm wrong but that test appears to be testing the channels directly fitted to studs? The IsoMax channel system doesn't do that... there is no DIRECT contact with the joists, the channel is contained within the rubber clip.

Read the report that I mentioned again: it has nothing at all to do with hat channel. It is about three different types of RESILIENT CHANNEL, which is an entirely different product. It looks like hat channel, but isn't.

there is no DIRECT contact with the joists, the channel is contained within the rubber clip.

That's exactly what RC does! It DECOUPLES the drywall from the stud. No solid contact. That's why it is called RESILIENT channel, not HAT channel: because it provides a resilient mount for the drywall.

The Genie Clip system is similar, and the figures put forward by IsoMax and Genie Clip all present a convincing picture, and say they outperform standard resilient bar by up to 7db

Claims are a dime a dozen, unless supported by real data from independent testing in reputable labs. Besides, 7 dB is not that much. A reduction of 1 dB is not audible. A reduction of 3 dB is barely audible to most people. You need a 10 dB increase in isolation to get a subjective drop to half the level (in other words, it sounds half as loud at 10 dB less). So 7 dB gives you, subjectively, maybe a quarter drop in level. A well-built MSM wall can give you 65 dB of isolation, which is 35 dB better than a typical house wall, and 20 dB better than your best RC wall, and 15 dB better than your best clip+channel wall.

Have third party tests been done on IsoMax or Genie Clip specifically to disprove those claims?

No idea. If it has, then it's up to the manufacturers to publish it. Or not publish it, as the case may be. If they don't, then that says a lot about their product, right there...

from what you're saying that would ONLY come in to effect if you had sheathing both sides?

No. What I'm saying is that RC, IsoMax, RSIC, and other similar products are designed for the case where there is an existing wall that has drywall on both sides, and greater isolation is needed. Take the drywall off one side, add the RC or clips+channel, put on new drywall (maybe even two layers, for maximum performance), and you get an increase of up to 15 dB in isolation with RC, perhaps a bit more with clips+channel. That's it. That's the purpose of these devices, and they work very well when used for that purpose. Since the original wall probably got around 30 dB, with a lot of luck, if it was well built, the update wall will get maybe 45 dB. On the other hand, a properly built fully decoupled 2-leaf MSM wall will easily get you 50, perhaps 60, and maybe even 65 if you build it very carefully with a large gap and plenty of mass.

If you read that report carefully, you'll see that the limiting factor for all resilient solutions is that the resilience of the device works IN PARALLEL with the resilience of the air, thus making the entire MSM system LESS springy (stiffer). That places a physical upper limit on how much isolation can be achieved with ALL such devices: it does not matter how you make the device, nor what materials you use: it will ALWAYS provide less isolation than the same amount of air would, simply because anything such device has GREATER stiffness than air, and that stiffness is ADDED to the air stiffness. You can't beat physics with marketing! There is a physical, real, absolute limit to what a resilient mount can achieve, and all other factors being equal, it can NEVER match, nor even come close, to what air alone can do. Read the paper, especially equation (6), to understand why this is always true, for all resilient mounts, regardless of how much money the advertising and marketing guys spend....

Here's what the report actually says about this: "The addition of the stiffness of the resilient channels increases the total stiffness and increases the resonance frequency above that for a similar situation without resilient channels. It will also limit the minimum stiffness and hence the lowest resonance frequency for larger air spaces." Take a close look, and read through to the end of the paragraph. It's quite clear and unequivocal.

Another interesting paragraph: "The measured resonance frequencies for all 8 constructions are given in Table 1. As expected, these resonances tend to be at higher frequencies than would occur for the same cavity without the added stiffness of the resilient channels." Yup. There you have it. The added stiffness of the resilient mount INCREASES the MSM frequency, and therefore REDUCES isolation, as compared to the exact same wall built with ONLY an air gap (without the resilient mount). It could not be more clear cut than that!.

Well it's a moot point if I don't actually go with the IsoMax system, as I would go with my original plan of 100mm stud. The only reason I was looking at 50mm was due to the IsoMax.

It's not a moot point: neither 50mm nor 100mm joists are capable of spanning any great distance with the live load and dead load of a typical studio ceiling, and for typical spacing and deflections. Do NOT try to build your ceiling until you get professional advice on the type and dimensions of the framing you need up there. It might actually turn out that you can use 100mm if the spacing is low enough, the deflection is unrealistically high, or the load is minimized. But you'll never know unless you get professional advice. It's not a good idea to hang many hundreds of kg of stuff over your head, if you have not done the due diligence to ensure that it won't collapse on you one day, and kill you ore seriously injure you...

Bottom line and the only real question I have is... am I better to go with 100mm stud decoupled from the wall, or 50mm stud with IsoMax? The answer to that seems obvious actually, but is there ANY reason you would use IsoMax in my scenario, or would it always have an inferior result?

You do not have a stud wall there to start with, so IsoMax clips are not the solution! Plane and simple. You said you have "brickwork" walls, not stud walls, so the solution is simply not applicable to your case.

Sorry, yes you're right... I'm confusing myself and thinking this is two walls within the same room.

Just to clarify: You already have single-leaf walls around your studio area: those are the brick walls you mentioned. That's one leaf. All you need to do is to add the SECOND leaf, which is a stud-framed wall-plus-ceiling that is decoupled from the brickwork and ceiling above, and has drywall on only ONE side of the framing. That's the same thing that Rod is describing.

- Stuart -

I have updated my location now, sorry about that.

Just to provide further details on the room also, it is exactly 2.75m x 5m with a height of 2.6m, which is to the lowest point of the underside of the concrete floor above. The floor needs to be raised and leveled (with insulation added as per building regs), which will be done with screed. This will raise the floor by approximately 175mm. I had initially considered a floating floor, but from reading Rod's book that doesn't seem like an optimal solution.

Below is a picture of the space at present... as you can see it's a blank canvas. The old ceiling joists still need to be removed. The door you can see at the back left is the door to the hallway of the house. This is a thick fire door. I am considering adding another fire door on the inside, and one or both of these can have acoustic seals added if necessary.

As to my budget, this is flexible... I do not have a bottomless pit of money but I have factored in a ballpark of £3000 ($4000) or so to do all the works, much of which will be done by myself... apart from the floor screeding and any electrics.

Get a sound level meter. Measure the actual level. That's how loud you are. Get a copy of your local noise regulations. That's how quiet you have to be. Do the math.

The problem there is obviously the room is just a bare shell. I don't know how measuring would help at this stage?

According to the UK Government website, permitted noise levels are; 34 dBA (decibels adjusted) if the underlying level of noise is no more than 24 dBA and 10 dBA above the underlying level of noise if this is more than 24 dBA.

In my experience though, excessive noise seems to be a qualitative measure rather than quantitative one. If someone complains and the 'noise police' come round, they don't record the decibel levels. They simply use their own judgement to decide if you are overly loud. Regardless, I want to avoid as much noise leakage as possible so that never becomes an issue... yet I'm obviously aware an excessive enough volume could negate any sound insulation solution I have in place.

GG is a CLD (Constrained Layer Damping) compound. It does not add mass to the wall. It works by damping the bending waves in the sheathing. If you don't know what bending waves are, then you could google that. TecSound is flexible mass, similar to MLV in concept. It is not a CLD. Two entirely different principles. TecSound also provides no usable acoustic data on their products, so it is impossible to say how well they work. I have no doubt THAT the work, but without independent test reports from a reputable lab, there's no way of knowing of the results are fantastic, mediocre, or disappointing, nor way way to judge value for money. On the other hand GG provides mountains of data on their products, from many sources.

Thanks. So in my situation, should I be more concerned with mass or damping? How do I make that determination exactly, if the effects of GG vs TecSound are that different? Mass is certainly emphasised heavily in Rod's book as being a crucial factor.

No. What I'm saying is that RC, IsoMax, RSIC, and other similar products are designed for the case where there is an existing wall that has drywall on both sides, and greater isolation is needed. Take the drywall off one side, add the RC or clips+channel, put on new drywall (maybe even two layers, for maximum performance), and you get an increase of up to 15 dB in isolation with RC, perhaps a bit more with clips+channel. That's it. That's the purpose of these devices, and they work very well when used for that purpose. Since the original wall probably got around 30 dB, with a lot of luck, if it was well built, the update wall will get maybe 45 dB. On the other hand, a properly built fully decoupled 2-leaf MSM wall will easily get you 50, perhaps 60, and maybe even 65 if you build it very carefully with a large gap and plenty of mass.

OK, makes sense. In my property, there is no drywall. The walls are all brickwork and plastered. I know this as we pretty much stripped the house when we bought it due to the state it was in. So in the garage, looking at the photo above, the left and rear wall (which has my bedroom behind it) are a single layer of breeze block with about 1/4" of plaster on the other side. That's it. The wall on the right, which has the neighbour's garage on the other side, is a double wall (i.e they have a separate wall on their side), with a likely air gap in-between. I can't know 100% if there is an air gap there as I can't get access to it, but a builder friend has told me this is probable as that's typically how it would have been constructed (house was built in late 90's).

It's not a moot point: neither 50mm nor 100mm joists are capable of spanning any great distance with the live load and dead load of a typical studio ceiling, and for typical spacing and deflections. Do NOT try to build your ceiling until you get professional advice on the type and dimensions of the framing you need up there. It might actually turn out that you can use 100mm if the spacing is low enough, the deflection is unrealistically high, or the load is minimized. But you'll never know unless you get professional advice. It's not a good idea to hang many hundreds of kg of stuff over your head, if you have not done the due diligence to ensure that it won't collapse on you one day, and kill you ore seriously injure you...

Yes that is valid... I have checked on span calculators and given the distance I am covering I will need a thicker joist for the ceiling, and I will also be sure I'm OK with weight tolerances before proceeding.

The problem there is obviously the room is just a bare shell. I don't know how measuring would help at this stage?

Read what I said one more time: "Get a sound level meter. Measure the actual level. THAT'S HOW LOUD YOU ARE. Get a copy of your local noise regulations. THAT'S HOW QUITE YOU HAVE TO BE. Do the math." Think it through, and you should be able to come up with the answer... I'll even give you a hint: If you are driving your car at 110 km/h, and the speed limit is posted as 50 km/h, how much to you have to slow down to abide by the regulations?

According to the UK Government website, permitted noise levels are; 34 dBA (decibels adjusted) if the underlying level of noise is no more than 24 dBA and 10 dBA above the underlying level of noise if this is more than 24 dBA.

Cool! So you already know the answer to ""How quite you have to be". Now you only have to measure "How loud you are", and do the math.

Thanks. So in my situation, should I be more concerned with mass or damping? How do I make that determination exactly, if the effects of GG vs TecSound are that different? Mass is certainly emphasised heavily in Rod's book as being a crucial factor.

Once you know the most basic number for your entire build (see above), you'll be able to answer your own question by using the equations for isolation as related to MSM walls. You are going to need them sooner or later, so I'll give you the complete set now:

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The equations for calculating total isolation of a two-leaf wall are simple:

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

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

Where: M = Surface density in kg/m2

For a two-leaf wall, you need to calculate the above for EACH of the two leaves, 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)

(Of course, if you don decide to use resilient mounts in addition to having decoupled framing, then you would have to account for the increased stiffness using the additional equation in NRCC-44692, since that places a lower limit on resonant frequency, and therefore places an upper limit in possible isolation).

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.

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You will likely need to repeat the above calculations using several different gaps and masses, until you arrive at a solution that allows you to achieve the isolation number that you calculated right at the start. You can make build up the mass any way you want, but it simply makes sense to do so with the least expensive materials, which is usually drywall in most parts of the world. TecSound is probably much more expensive, kg for kg.

You MIGHT also need GG, if your build happens to have the set of circumstances where it would be useful. But GG is also expensive, so you'd only use it if you need it, and can afford it.

So in the garage, looking at the photo above, the left and rear wall (which has my bedroom behind it) are a single layer of breeze block with about 1/4" of plaster on the other side.

Great! So that's a single-leaf wall. However, it does have cavities inside, which can mess up the isolation due to resonance, but that probably won't be too much of an issue. DO you know if the cavities in the breeze block are filled with sand, or just left empty? My guess is "empty".

The wall on the right, which has the neighbour's garage on the other side, is a double wall (i.e they have a separate wall on their side), with a likely air gap in-between. I can't know 100% if there is an air gap there as I can't get access to it, but a builder friend has told me this is probable as that's typically how it would have been constructed (house was built in late 90's).

That might be a problem, since it is already a two-leaf wall, so when you build your inner-leaf, that will make it into a three-leaf wall. which can potentially reduce isolation. You might need to add additional mass to your inner-leaf wall on that side, or increase the size of the gap, or both, to compensate.

Yes that is valid... I have checked on span calculators and given the distance I am covering I will need a thicker joist for the ceiling, and I will also be sure I'm OK with weight tolerances before proceeding.

Right. 2x4 ,umber (100mm joists) are not going to be able to span 2.75m safely at 600mm OC, and would be borderline at 400mm OC, assuming the typical live load and dead load for studios.

- Stuart -