Air Space Behind Bass Traps

Among other acoustic treatments, we're planning to build a large (8'x8') bass trap at the back of our control room and our question is whether it would improve the low frequency absorption by staggering two layers of 4" unfaced 705 panels with a 4" air gap between the two fiberglass layers and another 4" air space between the second layer and the wall, versus 8" of 705 with an 8" gap behind. I couldn't find an answer in the posts I searched.

Gapping is done for cost reasons. Solid 703 would probably cost about the same as the gapped 505 you are suggesting. Other materials may be significantly cheaper. Andre

Cojonesonasteek wrote:

and another 4" air space between the second layer and the wall

I think one contiguous air gap is best. Figure how much total space you can give up, then have 703 or 705 for half of it, and a gap for the other half. --Ethan

Thanks, that will be a little easier to frame out without the staggered panels.

Andre and Ethan, Are you two on opposite sides of the coin here? Andre always suggests going with cheaper materials and filling up the entire space whereas Ethan tends to always mention the air gap. Am I misreading this or are you two under a difference of opinion here?

awilki01 wrote:

Andre and Ethan, Are you two on opposite sides of the coin here? Andre always suggests going with cheaper materials and filling up the entire space whereas Ethan tends to always mention the air gap. Am I misreading this or are you two under a difference of opinion here?

No. Read this if you have problems with what Ethan and I write about materials and gapping. People at this level have problems even reading Ethan's articles about room treatment where he writes that 703 is a generic term and to look for HVAC suppliers for the material. I have lost count of how often I have linked Bob Golds Absorption Page telling people to look at performance and best price in their area. How low do you go? No pun intended. In the last three weeks I have helped people in the States to find suppliers of 703 like material by using web searches for commercial insulation suppliers. In case you have not noticed, I am in another country. My secret to success is knowing online yellow pages and looking for commercial insulation suppliers (as clearly stated in Ethan's articles). Do not think this is a slight to Americans. Less than than 12 hours ago I was talking with fellow music addict that I met through an AES meting and he was asking me if 703 is available in Canada and where to get it. Assuming that you read the linked thread, it is hilarious because the Roxul plant is one phone dialling area away from both of us! Do not ask generalities, or imply animosity where you do not understand what is being written. Ask more specific questions! Andre

Imply animosity or do not understand what is written? I think you are reading something into what I am writing that I am not intending. I also am understanding what I am reading, but I am also subject to information overload and many different theories. I am trying to get the information I need to make the best decision when making and hanging my panels. Regarding the material itself, I have found a place here in Dallas that supplies what I need. 4" - 4 pound Fibrex mineral wool panels is what I am getting based on price.

AVare wrote:

Do not think this is a slight to Americans.

Aw, go ahead and insult us. Most of us are just a bunch of dumm redneck yahoos anyway. Hey, look who got elected president - twice! :) --Ethan

awilki01 wrote:

Andre always suggests going with cheaper materials and filling up the entire space whereas Ethan tends to always mention the air gap.

Both approaches are good. Filling the space with insulation and using twice as much material absorbs bass a little better, but only a little. So if cost is not the issue for you, go ahead and fill the space. But not if that means you need to have fewer bass traps. In that case use half as much material with an air gap the same size, to have twice as many traps total. Is this clearer? --Ethan

Clearer, yes.....not yet crystal though :wink: I'm going with 4" material regardless. So, with that being stated, a 4" air gap would be better with this 4" material than no air gap at all, correct?

awilki01 wrote:

Clearer, yes.....not yet crystal though :wink: I'm going with 4" material regardless. So, with that being stated, a 4" air gap would be better with this 4" material than no air gap at all, correct?

Did you read my first post in the linked thread? If are willing to devote 8" of space, look for a safe n sound like product and fill it for a fraction of the of 703. Andre

AVare wrote:

awilki01 wrote:

Clearer, yes.....not yet crystal though :wink: I'm going with 4" material regardless. So, with that being stated, a 4" air gap would be better with this 4" material than no air gap at all, correct?

Did you read my first post in the linked thread? If are willing to devote 8" of space, look for a safe n sound like product and fill it for a fraction of the of 703. Andre

Andre, I had already read this post a couple days ago. I have been doing quite a bit of research on this site and others. I did look up Safe n Sound and it seems as though it is Canada centric. I'm too green to know what a similar Safe N Sound product would be. I found a local supplier in Dallas for Fibrex mineral wool and OC 703/705 panels. Money is important, but I'm not going to let it drive my decision into getting inferior products. I have my limit but the prices quoted me for the 703 and 4# Fibrex mineral wool will not come close to breaking me. Where I come from, you truly do get what you pay for more often times than not. And, the idea of filling in an 8" space full of material on my wall does not appeal to me from an aesthetics point of view. Back to the question..... Money aside, if I got 4" of Fibrex mineral wool or OC 703, a 4" gap would be better than no gap, correct? That's all I'm asking. I'm 99% sure of the answer, but I just want that 1% of doubt to go away. Everything I'm reading indicates it would be better, but I just want someone to tell me that I am on target....

awilki01 wrote:

Andre, I had already read this post a couple days ago. I have been doing quite a bit of research on this site and others. I did look up Safe n Sound and it seems as though it is Canada centric. I'm too green to know what a similar Safe N Sound product would be. I found a local supplier in Dallas for Fibrex mineral wool and OC 703/705 panels.

I'll some digging. What brands are available in your area?

Money aside, if I got 4" of Fibrex mineral wool or OC 703, a 4" gap would be better than no gap, correct?

Yes. Andre

Safe n sound is 2.5 lb/ft^3 insulation, in generic terms. SPI has an office in Austin, if you have not contacted them. Johns Mannville, Knauf. Owens Corning, amongst other brands. Andre

awilki01 wrote:

if I got 4" of Fibrex mineral wool or OC 703, a 4" gap would be better than no gap, correct?

Yes, and the explanation is here: http://www.ethanwiner.com/acoustics.html#air%20gap --Ethan

AVare wrote:

Safe n sound is 2.5 lb/ft^3 insulation, in generic terms. SPI has an office in Austin, if you have not contacted them. Johns Mannville, Knauf. Owens Corning, amongst other brands. Andre

I'm using the SPI office in Dallas and they only have OC 703/705 and Fibrex mineral wool. Thanks everyone! And, thanks Ethan for the simple 'yes' I was looking for....... Regards, Adam

We went with 6" of 703 and 6" of air gap behind the fiberglass with a grand total of 72 s.f. of absorber surface area at the back of the control room. The traps are mounted flush with the ceiling and in one case flush with the back corner (the studio's door is in the other corner so the other panel is offset). Clients have said the bass response of the room is much tighter than before the installation of the new traps. We still have some modal issues in the center of the room (where the producer's desk is) and will address those with tuned absorbers (the room is 24x16x11 so we have a good deal of volume to work with).