Quick question before I install

[Fumblefingers]

Hi all. I am building a couple of broadband absorbers....I think.

I made a 2'WX4'HX4"D box/tray and a 2" deep one. I have the 1" rigid fiberglass panels and will put 4 in the 4" and 2 in the 2". I have a nice brown burlap to cover.

Now.......my studio is tiny and there is a lot of 2" Auralex and Sonex in there. I really do not have the room for a lot of 4" panels, so I built one deep one for the lows and a 2" I figure might grab a slightly higher freq. Hoping...LOL.

I did a Room EQ Wizard test with and without the panels ( uncompleted and just leaning...the fiberglass nesting in place but without the burlap screens ) and I can see a visible difference where the graph is more flat with the panels in. So I know they are making a difference. I will post on that later with images and ask you guys to help me decipher the readings.

My question is about the back and the mounting.The trays are 1/2" plywood sides with 2-3/8" holes all the way around, 20 in all....on the 4". I have yet to put the (smaller) holes around the 2" tray.

The back of the trays is regular luan. It is a tad less than 1/4" thick as measured.

Because of available space I am mounting these on the rear wall behind the desk. I have Auralex LENRD's in the upper rear corners....yeah I know....I might replace them with more screens later. Problem is there is electrical stuff in the corners, a fuse box and outlets...I cannot cover these...so I am a bit boned there.

Anyway.......finally my question...sorry to be long winded.

Should I.....A) Drill holes in the back? B) mount the panels flush against the wall or leave an air gap? If air gap.....how much?

I am about to start the finish work.....painting etc and want to hang these while they are unfinished so the weight is more manageable...I am working on my own...no helper to hold in place.

[DanDan]

Long description indeed. However quite clear.
Most treatment panels have no backs on them. They are just a frame.
I recommend that you remove the backs or drill holes equal to at least 30% of the area. Some of us are convinced that it is worth spraytac gluing a film of plastic or paper to the back to enhance LF absorption.
The airgap is a free lunch. More is better. Corners often have the most bass, so traps straddling them are very effective, plus a big gap.
Two traps is very little so I suggest that you make the most of them.
Take a look at your measurements. The Waterfall should show the strongest rooms modes clearly. Lets guess you have one at 45 Hz, another at 73Hz.
73Hz is right in the Kick Bass zone, so lets focus on that. Play a sine wave at 73Hz. Try to find a spot, maybe a ceiling corner, maybe the middle of a wall, who knows, where it is really loud. Put your Bass Trap there.
DD

[Fumblefingers]

Thanks, Dan....good info. I will put to practise.

[Fumblefingers]

So DanDan, I cut 3 one foot circles out of the backs of both traps. These 3 circles are less than the 30% that you mentioned some of you guys like to see but it should help a bit.

Space is a huge factor....I am going to mount these away from the wall by 1-1/2" for the 4" and 1" for the 2" trap.

I am just going to burlap over the holes and not do any sort of a membrane.

Thanks.

[DanDan]

In every detail there more would be better, but you can only do your best.
Good luck with it.
DD