# Best panel assembly for a soundproofing barrier

What are the properties of the best barriers for general outdoor noise?

1. Number of reflective panels
How much does the number of panels affect STC (sound transmission class rating)? Many sources claim that removing drywall layers can improve STC.

d = drywall
s = studs
f = fiberglass
a = air space

• Assembly 1:  d, s + f, d, a, d, s + f, d:

• Assembly 2:  d, s + f, a, s + f, d:

They claim assembly 2 has a higher STC than assembly 1.

2. Absorptive layers
I heard they help between reflective panels. They can't be used in the middle of a window because they block the view.

3. High ρₛ (mass / area) and low stiffness is best for 1 panel.

4. Panel variety
Is there a benefit to using a variety of materials?

Reducing coincidence effect
I think this has to do with the relationship panels have with each other, ρₛ, and stiffness.
For a simplified version, what panel thickness ratio is best given they're the same material?

• Are you asking why removing drywall from an assembly can improve STC? The STC values for these assemblies have been determined experimentally and are not disputed, so if you’re skeptical, then we can say that yes, more drywall layers can be bad for STC. Aside from that, it would help if you can edit this to include on clear question. Right now I’m not sure what your question actually is. Commented Sep 2, 2023 at 23:09
• 'general outdoor noise' is too vague. If you mean kids playing in the street, then fine, but if you mean trucks passing 5 yards away, this won't help in the slightest. Aside from that - panel variety, yes. Each plane should have a different resonant frequency. All construction should be floated on engineering rubber/neoprene. For trucks or neighbours with poor taste in music, you need considerably more mass. Commented Sep 3, 2023 at 9:19
• Intuitively, two hard surfaces like plasterboard in close parallel would vibrate in sympathy, adding to sound transmission. You want to break that kind of interaction as much as possible. Rigidity is the enemy if you don't have the critical mass. That being said, there are a lot of curves on this graph, and I'm no expert. Furthermore, we don't really like to talk about construction on a sound design community :)
– n00dles
Commented Sep 3, 2023 at 19:00

For my studio design needs I mostly use John Sayers' forum and handbook. (The forum is up for now but it had gone dark for a period of time. In case this happens again this great Reddit member got us covered with an archive of the forum!)

In there (handbook), you can find STC charts for various designs and materials.

In general, it's a very good and extensive book on studio design & construction along with the forum that has a lot of great information and projects. Not sure if it's very lively but the information is there.

Specifically for the design you mention (2), there are 3 STC measurements in the handbook:

As someone would expect these measurements and examples come with the following disclaimer:

But of course, you can find all that in the handbook I shared above, it's a good idea to download it and keep it as a general reference :)

Also, keep in mind that when stacking plasterboards you should not align the edges, meaning that when 2 plasterboards connect on layer one this connection should have a full plasterboard covering it thus throwing the connection of this layer's plasterboard on another point. This helps with keeping things airtight!

I will just mention that walls alone won't cut it, especially for mechanically transmitted noises, you'll need to work on the ceiling and floor as well.