Recommended Air Gap For Back Wall Panels?

[mrfye17]

Hi People,

I have a room 11' 6" x 18' and have already installed Sofits (17" x 17") Floor to Ceiling on all 4 corners as well as Wall / Ceiling corners.

Side panels 2' x 4' x 6' deep with Roxul Safe'n'Sound for RFZ are done and will be putting up a ceiling cloud with same type of Panels.

I will be using these 2' x 4' x 6" deep panels also for the Back Wall.

My Question is....

How much of an Air Gap shall I allow between the Back Wall and the Panels for most effectiveness? 4", 6" or more?

Thank you to everyone in advance.

[Gregwor]

Air gaps will help. Add as much as you can afford space-wise. It's not entirely necessary but again, it will help if you can have a gap.

Greg

[mrfye17]

Thanks Gregwor.
Is there any reason not to have an Air Gap on the Back Wall, in this case, or is that just a Silly question?

[Gregwor]

The gap will help a lot with thinner amounts of insulation. For thick insulation (like you'll have on your rear wall), the air gap doesn't help nearly as much.

4" of insulation with a 1" gap:

4in with 1in gap.png

Now, see how little the air gap helps when we have 24" of insulation with a 1" gap:

2ft with 1in gap.png

Greg

[DanDan]

We are only guessing really. Gap:fibre of 16:1 works really well with a full boundary, e.g. suspended ceiling.
If you are doing full boundary, these calculators should be accurate. But they do not cover the boost in absorption in a corner, or the loss of absorption when say a 4" trap is alone and away from the boundary wall. I would suggest that for traps with gaps between them, 1:1 is probably a good bet.

[mrfye17]

Thanks DD. You've helped me greatly on previous threads. The traps are 6" deep (Rockwool Safe'n'Sound)

What would you suggest for Ceiling cloud?

I only have a Height of 8 feet. Does a 1:1 gap ratio still apply and will there be a benefit angling the panels? If so, then what angle would be appropriate? Panels are 48" x 24" x 6" deep and putting 4 of the across the top from left to right.

[DanDan]

6" is a fine depth of cloud and 4 across is a good area. But as always acoustics would be very happy to cover the whole ceiling.
Vertical modes are very intrusive especially when your ears are at half height.
1:1 would be great, perhaps if you were to include lighting in the cloud it could help with height. If the full 12" is untenable just do your best, go as far as you can. Angling is a way to score some depth while keeping some height I guess, but on the other hand it is reducing the air gap. Not sure if it really of much or any benefit. Some acousticians have promoted hard backed angled clouds, to break up the vertical modes.
Many of these techniques don't really get properly tested, e.g. soft cloud vs hardbacked, angled vs flat.

[mrfye17]

Thanks once again DD

[Gregwor]

will there be a benefit angling the panels? If so, then what angle would be appropriate?

There will always be some percentage of reflected sound from any surface. As I'm sure you've understood by now from reading on the forum, low frequencies will easily penetrate through insulation (that's why it takes such intense construction to isolate low frequencies!). Lower frequencies can be reflected using very hard and heavy materials. So, the idea is to place a heavy hard surface on the backside of a ceiling cloud and angle it such that frequencies are reflected towards your rear wall (over top of your head/ears). With thick effective insulation on your rear wall, we are able to attenuate and delay any reflections we hear enough that it won't have a negative impact on our listening position.

Greg