The thing with double layer is that you don't align the joints all at the same spot and therefor reduce leakage. The more mass the more isolation you get so double 15 is better than double 12.5. Is it Worth it ? It depends on how much ambient noise you have in your neighborhood. Close to an highway ask for more than a quiet place...
Having more mass without it being sealed perfectly won't help. But if you have the expertise to do perfectly filled joints, the SoundBloc seems to be an interesting product.
Combining it with other products might be risky if they don't react the same to weather and humidity ; one may break the other. I'd ask the maker if such combinaison is recommanded or to be avoided.

Note that I'm far from an accoustic specialist...

pcrecord, post: 440239, member: 46460 wrote: Note that I'm far from an accoustic specialis

me neither but i do know when doing double layers of rock it's better to go with one layer of 3/4" or 5/8"and one layer of 1/2" and as the previous post mentioned, stagger the joints. it's also best to use construction adhesive to bond the layers together to prevent rattles and resonant vibrations.

Kurt Foster, post: 440250, member: 7836 wrote: it's better to go with one layer of 3/4" and one layer of 1/2"

Noted, good to know but... Why is that?

different thicknesses of sheet rock have different resonant frequencies. same thing as with a window. (different thickness on each side).

Kurt Foster, post: 440250, member: 7836 wrote: me neither but i do know when doing double layers of rock it's better to go with one layer of 3/4" or 5/8"and one layer of 1/2" and as the previous post mentioned, stagger the joints. it's also best to use construction adhesive to bond the layers together to prevent rattles and resonant vibrations.

You should not use construction adhesive between the layers, it reduces the TL of the wall. You can use Green Glue which dampens between the layers and increase the TL of the assembly.

dprimary, post: 440279, member: 15341 wrote: You should not use construction adhesive between the layers, it reduces the TL of the wall. You can use Green Glue which dampens between the layers and increase the TL of the assembly.

Agreed.

Here's what I've got so far:

When you consider how much floor space you will lose doing a double wall assembly everything has to be taken into consideration.

You have to think of the ceiling as a wall too. You are going to be building a "room inside of a room". You ceiling of the
interior framing should be a completely separate frame from the roof.

Sound wants a lot of space to fully bloom so with that in mind, I personally would get rid of the angled wall and use as much of the building as possible.

Thanks Brien. The image is confusing: the angled wall is actually the four inner stud walls propped up, awaiting installation. When finished, it will be a normal, rectangular room with double stud all the way round.

- Is 15mm worth the extra cost than 12.5mm if you double them up?

There is current data that supports the "thicker / mass is better" so yes the firerated 5/8 or 15mm is better at generating isolation assemblies that contain the low frequency and the high frequincies as well.

- You can get thicker, acoustic plasterboard like this. Does this work as double thickness? Could you use a combination of one layer drywall, one layer specialised acoustic plasterboard?

Yes it does and yes you can. What would have to ferreted out is what will this configuration generate in respect to the Tl of the assembly. But mass and density are what you keep your eyes on.

- Is two layers of standard drywall theoptimal configuration here?

Again...mass is your friend. And two layers has supported data and is based on mass law that states for every doubling of mass you can expect a 6 dB increase in isolation. So if you wanted to generate a higher TL with your current assembly you would have to double the mass. E.g. 2 layers becomes 4 layers...4 layers becomes 8 layers 8 layers becomes 16 layers...etc. etc. Still only recieving a 6 dB bump with every doubling.

- The studs are up and ready to go, so if you were in this position, what would you install on the inner stud for optimal sound containment?

Me personally...I would install OSB as my first layer. This gives you an interior structure that can support itself without tje need for isolation braces. Now in your country you may or mayNOT have this flexability. You may live on a fault line like say Chile, where it would be expressedly forbidden....and everything is concrete anyway.

And you an install treatments as needed at precise locations thanks to the plywood or OSB whichever is used.

Thanks for the reply. Are you suggesting OSB as the first layer of INNER stud, and then a layer of dry wall on top of that? Would that be superior to double drywall?

This gives you an interior structure that can support itself without the need for isolation braces. Yes do it as the first layer. But the density of osb or plywood is not the same as sheetrock so you would still install 2 layers of rock.

To match the density of sheetrock you would have to use MDF...and while it can be used it is offered with much caution because MDF will break down from moisture and moisture is always an inherant side effect of building high thermal assemblies of which sound proofing falls into this catagory.

Brien Holcombe, post: 440290, member: 48996 wrote: moisture is always an inherant side effect of building high thermal assemblies of which sound proofing falls into this catagory.

(y)

JCurtisDrums, post: 440234, member: 48753 wrote: - Is 15mm worth the extra cost than 12.5mm if you double them up?
- You can get thicker, acoustic plasterboard like this. Does this work as double thickness? Could you use a combination of one layer drywall, one layer specialised acoustic plasterboard?
- Is two layers of standard drywall the optimal configuration here?
- The studs are up and ready to go, so if you were in this position, what would you install on the inner stud for optimal sound containment?

-Standard fire rated 5/8" double or more is the best performance for the dollar with reguard to isolation bar none.

-The optimal amount of layers of the fewest number of layers that brings the isolation to acceptable / legal tolerance. Two drywall layers is considered the minimum since one layer of drywall is simply a standard wall. Your also restricted by what's holding the drywall up like clip/channel systems max out at 2 or 3 layers. A double stud wall maxes out at much more.

- I can't tell what the room dimensions are. Double stud takes the most space, but is simultaneously the cheapest and most effective for isolation.

RISC -1 clips aren't the cheapest but outperform channel systems and can support a third layer, which resilient channel can't.

Green glue is a proven product at the cost of 1.5x a drywal layer roughly. If your paying for labour it could come just equal to a n additional layer.

Resilient channel is the least space consuming and least effective method while also being only about 30-40% cheaper roughly, than the alternatives not counting labour. Adding only 3-5 db of isolation with a high chance of error for installation it's my last choice.

All in all double stud is the simple way to go and the most cost effective, while taking up the most space, it offers the highest isolation. That double stud assembly adds 20+ db of isolation from the get go.

Kurt Foster, post: 440263, member: 7836 wrote: different thicknesses of sheet rock have different resonant frequencies. same thing as with a window. (different thickness on each side).

For Windows the resonant frequency is a concern becuase there is a cavity. It's also why you have to over spec one of the glass sheets, becuase the thinner side will always be weak. So the weak side has to be as dense as the wall. The strong side should be the next size up. This gives you no resonant frequency issues or any weak links isolation wise.

I have seen Andre Avare, an excellent Canadian acoustician state that with glass this thick resonant frequencies aren't an issue. It was in response to me reccomending doffernt glass thicknesses.

With layers that are coupled like drywall on a wall, is all about mass. So becuase the two layers are essentially acting as one, their resonance is calculated as a whole. So two different thicknesses are weaker isolation wise, unless they equal more mass than two layers of the same stuff.

With reguard to construction adhesive, this also decreases isolation. Products like green glue are elastic dampeners so it's there non-hardened state that allows the drywall layers to act semi independently and dissipates engery. Construction adhesive does not allow for this and weakens the assembly as a whole. So green glue is the only stuff to use in between drywall layers.

Windows are often weak spot in walls, what did you plan there ??

pcrecord, post: 440304, member: 46460 wrote: Windows are often weak spot in walls, what did you plan there ??

Double glazed laminate upvc window on the outer shell, secondary inner glazing on the inner.