A couple of quick questions

[tonium]

First off, I'm building a new studio, and I have most of the acoustics and building work planned out. This forum has been an excellent resource, but sometimes you just need a few quick answers to simple questions

1. Should I place the timber frame of the inner leaf on neoprene matting. I see some people doing it and some not. If so, I am based in Sydney, Australia so if any one can suggest an appropriate product, that would be great. In terms of Mass, Walls will be 90mm Timber frame, Earthwool R2.5, Fyrcheck 16mm with a max height of 3m.

2. How are people lighting and providing power to their studios? Cutting a hole in what was previously a sealed wall seems counterintuitive, so I imagine a fair amount of green glue has to seal the hole back up once the cables are pushed through? And what about power points?

I can provide the Sketchup plans if needed, but I didn't think they would be needed in this case....

[Soundman2020]

Hi "tonium", and welcome to the forum!

1. Should I place the timber frame of the inner leaf on neoprene matting. I see some people doing it and some not.

Only if you do it right! Technically, that is "floating" the wall, and has to be done carefully, after the relevant calculations have been done. Basically, you need to determine the total mass of the wall plus everything that will be attached to it, and use that to figure out the type of rubber you will need, how thick to make it, and how wide to make it in order that it will be compressed just enough to cause the correct deflection, and therefore actually "float". If you don't load it enough, then the rubber does not compress and the wall does not float. If you put too much load on it, then the rubber over-compresses and the wall does not float. Then, you also need to use isolated collars for your anchor bolts, and isolation washers, and you then need to torque the bolts just enough so that the washers compress just right (for the same reasons as above), and of course you need to consider the pressure that the bolts will be applying when calculating the initial rubber thickness/width/type. And finally, you also have to ensure that the drywall itself also floats, by keeping it well off the ground while hanging it, then partly filling the gap underneath with backer rod, and caulking the rest of the gap with acoustic sealant. You also need to take those into account in your calculations, since they constitute part of the overall resilient pad that is keeping the wall floating. So, if you think you can get all of that done correctly with no mistakes, then yes, floating your wall is an option. It will gain you a few decibels in isolation, with luck.

On the other hand, since your proposed wall structure isn't designed for high isolation anyway, it doesn't seem worthwhile going to all that trouble in your case. Floated walls and floated floors are only used when there is a need or a high level of isolation, which does not seem to be your situation.

In terms of Mass, Walls will be 90mm Timber frame, Earthwool R2.5, Fyrcheck 16mm with a max height of 3m.

You don't say what the outer-leaf is made of, or what the size of the air gap is, but at a guess I would assume you are aiming for around 40 dB of isolation?

2. How are people lighting and providing power to their studios? Cutting a hole in what was previously a sealed wall seems counterintuitive,

Exactly. That's why you can have only one single penetration for bringing the main power feed into each room, then all of the internal electrical work is done with surface-mount outlets, switches, lights, and ducts. No holes in the wall: everything is mounted on the wall, not in it.

so I imagine a fair amount of green glue has to seal the hole back up once the cables are pushed through?

Green Glue is not sealant, and it is not glue either. It is a visco-elastic polymer compound that is designed to do one thing only: act as a constrained layer damping material between sheets of drywall, plywood, fiber-cement, or other similar wall/ceiling/floor sheathing materials. It can't be used to glue things together (despite the name!), and it can't be used as a sealant either. The Green Glue Company also makes acoustic caulk, which is a sealant, but their flagship product is not what you would use to seal electrical work.

And what about power points?

Same as the switch boxes and light fittings: use surface-mount sockets. Take a look at the Legrand product range for surface mount electrical systems (also called "structured cabling systems" and "cable raceways" sometimes). Also Kalop (mostly in Latian America), Wiremold (although I think Wiremold is now Legrand), Panduit, Rialto, Wire Track, Electra-Base, and others.

I can provide the Sketchup plans if needed,

Definitely! It's always a good idea to have extra eyes looking over your design to make sure you didn't miss anything! Post some images form the SketchUp model here on the forum, and the model too, if it isn't too big. If it is too big, then post it on a file sharing service (Eg. Dropbox), and post the link here.


- Stuart -

[tonium]

Hi Stuart,

Thanks for the reply.

- That makes sense on the neoprene. So we will be leaving that out then.

- 40db reduction doesn't seem like that much, or am I wrong? The Air gap ranges from 5cm to 8cm, depending on wall angles. If I added a second layer of 13mm fyrchek to the inner leaf (first vertical and then horizontal) , would that give me much improvement?

- Earthwool R2.5 seems to be recommended by quite a few people, but how does it REALLY compare to Tontine Acoustisorb 3. The Absorbtion Co-efficients on the data sheets are identical all the way down to 125Hz, but any more 'hands- on' info would be helpful. The price difference seems to good to be true...

- The outer leaf changes on different sides. 2 sides are 1920's art deco brickwork that is at least 30 cm thick - which seems good. The others are internal gyprock, so pretty terrible as a starting point. Fortunately we have a corridor on the other side, before another studio. Still not ideal, but at least we have a bit of air.

- Your explanation of Electrical and Audio cabling thankfully matched my ideas, but I was going to have one entry point for electrical and another for audio, so that there was no chance of electrical interference ending up in my audio. Acoustic caulk (not green glue) will be used to seal the gaps.

- I'll look at all the electrical products you mentioned. Thanks for those.

- Attached is a link to the sketch up doc, which contains all the measurements on layers. I haven't put in all the walls so that I could look around! The windows will be double glazed 6mm, angled. All the doors open out into the corridor.

If you need any further information, I hope I can provide it!

- Ben

https://www.dropbox.com/s/clskd8y0abrs4 ... 0booth.skp

[Soundman2020]

- 40db reduction doesn't seem like that much, or am I wrong?

You are right! It's the starting point for home studios. A common house wall will get you 30-something dB of isolation, perhaps more, depending on how it is built, so 40 dB is only about twice as good, subjectively, meaning that sounds are about half as loud on the other side. A more common goal is around 50 dB isolation, which is twice as good again (subjectively), or ten time as good (objectively, in terms of the amount of energy you are stopping).

The Air gap ranges from 5cm to 8cm, depending on wall angles.

Careful! Don't confuse "air gap" with "framing gap"! If you have two stud frames for your wall, where the outer frame has drywall on the outside, and the inner one has drywall on the inside, and you have a 5cm gap bet ween the frames, then you have about 23cm of air gap: the depth of the studs themselves is "air", since the drywall is on the far side of those gaps. That's the gap that matters: the distance between the two "leaves" of the wall, measured from surface to surface across the wall cavity. Stud frame depth plus frame gap size. That's your total air gap, and is what the sound "sees", even if it is filled with insulation. Insulation is mostly air anyway, so is not considered when calculating the gap. In fact, technically, adding insulation increases the size of the gap as far as sound waves are concerned, because it forces them to take a longer path in crossing the gap...

If I added a second layer of 13mm fyrchek to the inner leaf (first vertical and then horizontal) , would that give me much improvement?

It would, yes, but switching to 16mm drywall for both of those layers would give you a bigger improvement, and filling the air gap completely with insulation (the right type, of course!) would also give you a good increase. The difference in isolation between a wall with no insulation and filled with insulation is usually around 6 to 10 dB, and can be as much as 16 dB, depending on the wall. That's a huge increase!

Adding extra layers of drywall not only increases your isolation, it also drives down the resonant frequency of the wall, meaning that it isolates better at lower frequencies where it was not isolating at all before.

- Earthwool R2.5 seems to be recommended by quite a few people, but how does it REALLY compare to Tontine Acoustisorb 3. The Absorbtion Co-efficients on the data sheets are identical all the way down to 125Hz, but any more 'hands- on' info would be helpful. The price difference seems to good to be true...

Well, like a lot of things in acoustics, this is not intuitive: Absorption coefficients refer to using the insulation as an acoustic absorber inside the room, as part of your treatment. They tell you roughly how well the material will absorb different frequency ranges, when one side of the material is pressed up against a hard barrier and the other side is exposed to the air in the room, and the sound waves are arriving mostly "normal" to the surface (hitting it head on). Unfortunately, that doesn't tell you a whole lot about how that same insulation will behave when you are using it as a resonance damper inside a resonant cavity sandwiched between two sheets of drywall! You'd think it would be the same, but actually... not so much.

What matters really for wall cavities, is how well the insulation damps sound at the resonant frequencies that will be happening inside the wall. The best indicator of that is something called "gas flow resistivity", which basically means "how well does this stuff resist air moving through it". It is measured in the wonderful obvious terms of "rayls", and of course everybody knows that 1 Rayl = 1 kg/(m2s) (Not!) It's a measure of acoustic impedance, and basically refers to the ratio between the applied pressure across the insulation and the particle velocity inside it. Wonderfully simple stuff, that everyone learns in primary school, right? And of course, if you go to your local hardware store, the salesman knows all about Rayls, and will be able to guide you to exactly what you need!

Of course, in reality this is one of the most obscure units of measurement ever devised, and even most manufacturers of insulation don't bother measuring it, because their products are meant mostly to be thermal isolators, not acoustic isolators! Only a very small number of manufacturers measure it, and publish it, since it is meaningless to the vast majority of their customers. Only us weird folks who want to build studios are interested, and we don't count: we by a tiny fraction of one percent of the insulation products out there...

Fortunately, it turns out that there is a rough relationship between gas flow resistivity (GFR) and a far more common measurement: density. The relationship isn't perfect, and isn't linear, and is different for each type of insulation, but is close enough to be useful. It turns out that if you use fiberglass insulation, then you need a density in the region of about 30 kg/m3, whereas if you use mineral wool, it has to be in the region of about 50 kg/m3.

If you really want to confuse yourself even more, then this explains Rayls: (sort of) http://en.wikipedia.org/wiki/Rayls

- The outer leaf changes on different sides. 2 sides are 1920's art deco brickwork that is at least 30 cm thick - which seems good. The others are internal gyprock, so pretty terrible as a starting point. Fortunately we have a corridor on the other side, before another studio. Still not ideal, but at least we have a bit of air.

OK. The brick will need sealing with some type of masonry sealant, or a coat of render, or even just a good coat of paint. You just need to seal the porous surface. I'm talking about the surface that will then be hidden inside the wall cavity: you don't want a porous barrier, for obvious reasons. The drywall will probably need beefing up with an extra layer. And in both cases, all gaps MUST be sealed with acoustic caulk.

- Your explanation of Electrical and Audio cabling thankfully matched my ideas, but I was going to have one entry point for electrical and another for audio, so that there was no chance of electrical interference ending up in my audio.

That's fine: no problem. The idea is to minimize the number of penetrations, to make your job of sealing them easier, and to have as few as possible potential points of failure.

- Attached is a link to the sketch up doc, which contains all the measurements on layers. I haven't put in all the walls so that I could look around! The windows will be double glazed 6mm, angled. All the doors open out into the corridor.

great! I'll try to take a look at that later today, and see if I have any comments...


- Stuart -

[Soundman2020]

Looking at the SketchUp model, it seems that this is just a rehearsal space, right? No control room? No recording/mixing? Just a single drum booth, plus a larger rehearsal room?

- Stuart -

[tonium]

- The 2 rooms that don't have the drum kit will be control rooms, sharing the live room. 1 will be mine, (the one with all the detail in, and the other will be someone else's) I did have some desk models in the control rooms, but they seem to massively increase the size of the sketch up file. The 'rug' was put in to give me some idea of the size of my current desk/chair setup, currently about 2m wide.

- Drums were put in for a size indication. I would love to be able to do drums, but the logistics (not on a ground floor) and budget won't allow us to get enough reduction into neighbouring floors. Maybe after office hours... If I owned the space (instead of leased) I would do a much more severe job. FYI - I have read nearly every post on floating floors, and we have to apply the same treatment to the floor of the booth. I know this may introduce some resonant frequency issues, but the isolation will be needed.

Careful! Don't confuse "air gap" with "framing gap"! If you have two stud frames for your wall, where the outer frame has drywall on the outside, and the inner one has drywall on the inside, and you have a 5cm gap bet ween the frames, then you have about 23cm of air gap: the depth of the studs themselves is "air", since the drywall is on the far side of those gaps. That's the gap that matters: the distance between the two "leaves" of the wall, measured from surface to surface across the wall cavity. Stud frame depth plus frame gap size. That's your total air gap, and is what the sound "sees", even if it is filled with insulation. Insulation is mostly air anyway, so is not considered when calculating the gap. In fact, technically, adding insulation increases the size of the gap as far as sound waves are concerned, because it forces them to take a longer path in crossing the gap...

So my current gap to the brick would be 9cm frame, plus 2 to 5cm of air, giving me 11 to 13cm of 'gap' from gyprock to wall. In the booth it would be 9cm frame + 5cm air + 9cm frame = 23cm. The frames are filled with isolation material (earth wool/acoustisorb).

16mm drywall for both of those layers would give you a bigger improvement, and filling the air gap completely with insulation (the right type, of course!) would also give you a good increase.

- 2 layers of 16mm will be used everywhere now. But we still need an an actual gap to the outer leaf, right? Otherwise we will get flanking from the inner to outer leaves?

The Earthwool has a density of 45 kg/m3 and the Acoustisorb is 48kg/m3. At $60 a roll instead of $300, that seems like a good deal...

Everything else makes sense, and will be applied. This information is MUCH appreciated.

[Rizza_81]

Where did you see Earthwool R2.5 is 45kg/m3?

http://www.knaufinsulation.com.au/en-au ... batts.aspx

Looks like it's only 20kg/m3 according to the manufacturer. The R2.7 is 27kg/m3 which they call their super high density insulation.

[tonium]

Where did you see Earthwool R2.5 is 45kg/m3?

On a post on this forum....

http://www.johnlsayers.com/phpBB2/viewt ... ol#p130021

I thought it was too good to be true! I will go to Acoustisorb 3, as that was originally budgeted for.

[stevev]

I thought it was too good to be true! I will go to Acoustisorb 3, as that was originally budgeted for.

Hey tonium, I looked around at a lot of insulation for my build and came up with Bradford Soundscreen as the best option. It's fibreglass and comes in at 24kg per m3. I don't think the Acoustisorb is anywhere near that density and from memory it's also polyester, which I don't think even Stuart has the gas-flow-resistivity numbers for The Bradford product was more expensive if I remember right and if you wanted to go the rolls-royce for insulation then it's a product made by Fletcher called FI-32. Semi rigid insulation. I didn't use it in the wall cavity (I used the Soudscreen) for my build as it was cost-prohibitive, but I did use it as the acoustic treatment in the control room and it's btilliant.

all the best.

steve