Hello there,
I recently moved and my new room needs some modifications.

On one side of the room the wall is thin drywall, on the other side it is a load bearing wall made of concrete. So I was thinking of bracing up the drywall to add some rigidity to the hollow portion of the room by adding an additionnal sheet of 25mm audio-adapted drywall but I am wondering if I should add a gap between and sheetrock, or directly screw the new 25mm dry wall onto the present one.

Any thoughts on that matter would be greatly appreciated

Have a good one.

When adding mass layers you don't leave any air gap between the layers.

Also use standard drywall and get the thickest size that readily available. Over here it's 5/8" thickness. Don't use any sort of "audio" branded drywall.

Hello there Kyle,

So no gap it is
Thanks for your advice.

Could you elaborate why I shouldn't buy audio specific dry wall ?
Is it not more rigid/heavy ?

Cost vs performance

Its only got a little extra mass vs a lot of extra cash

Also... if we are talking about a control room here, it would be best to have the mass imbalance in the front/rear vs left/right

Oh well that does that make sense.

So if I can get 2 sheet of drywall for the price of one and get an extra 10mm in the deal, it's the way to go ?

Correct, mass is mass, so whatever you can get cheap is best

note: if you buy 5/8" fire rated drywall (or other dimension - fire rated - some countries have up to 1 1/4"), you'll generally get a better density than regular drywall, or without the "magic" implied by "acoustics rated".

note: some "acoustics rated" drywall products mix in a damping agent which can improve its isolation characteristics - however you'd be wise to compare their [professionally] tested and published ratings (such as found in [professionally] tested and published assemblies) for that product, versus another type of damping, such as viscoelastic dampers (e.g. Green Glue), MLV, etc. in their [professionally] tested and published assemblies.

however, for general purposes, the 5/8" (15-16mm) "fire rated" (e.g. Type-X) drywall is a good first choice for readily found and cost-effective mass when building framed wall and ceiling assemblies.

Just to add to the others excellent posts, they area to focus on is low frequency performance. This is where often "acoustic" drywall or damping agents will not have an advantage, and will nearly never have the cost vs performance advantage.

If you could, try to mimic the mass of the individual walls to match as close as you can get. Not saying you have to put 20 layers of drywall to match the concrete wall, however getting close will minimize the differences in low end response between left and right.

One sheet of drywall is somewhere between 10kg/m² and 13kg/m², depending on the type, go figure

Thanks alot for that wisdom !
I will keep all of this in mind before making any purchase

Now if I put up multiple sheet of drywall, should I add a viscoelastic damper between each sheet such as "Green Glue" like @ gullfo mentionned ?

I never heard of this kind of products.

Each of these has its use case. Will drywall/green glue/drywall provide more isolation than drywall/drywall? yes it will. But it will provide less than 3 drywall layers, which will probably even be cheaper.

The most cost-effective mass is std building materials. The limitations come from the environment you work in. If your floor safely holds the weight of an additional concrete wall? Do it (as a matter of speech). Your floor does not support it? Make multiple layers of drywall. Not enough space for the extra layers? use MLV or green glue. This is in order of higher to lower effectiveness and low to high price :D. In all scenario's, consult your structural engineer before you start enforcing walls.

This is all assuming you have a single leaf environment (mass will be the most important driver for isolation results). Second driver is airtightness; close all gaps and cracks with sealant, baker rod, your favourite silicone etc, as long as it stays flexible over time.

If your requirements go further, then you go mass/air/mass, or room-in-room setups.

I'd have to double check, but I'm pretty sure GG in between 2x sheets of drywall equals 4 layers of drywall approximately. The difference is in the low frequencies where the equivalent drywall will outperform. GG does not lower the fMAM like additional drywall does.