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Can duffle bag bass traps work?
Old 1st August 2019
  #1
Here for the gear
 

Can duffle bag bass traps work?

Hello all! I have deeply enjoyed reading the forum for the last year, and now the time has come to stop lurking

I'm wondering about military duffle bags filled with insulation, and how well they can reduce low frequencies.
The bags are made from thick cotton canvas and barely let air flow through, so they cannot be good broadband absorbers, but am wondering if they can work effectively as low frequency treatment.
I've searched high and low, here and there with almost no results. There has to be a good reason I'm not seeing any mention these of these heavy duffle bags. It really seems like the fabric will reject all the stuff I need (highs, and some mids) in my tiny 9' x 11' issh room, but will absorb low frequency content.

Can they be effective in the same way as FRK panels?

If they are made from too dense of a material, then why not cut holes and use coffee bags on the inside to keep fluffy insulation in?

I like the idea of using 30" x 50" canvas bags because they come ready assembled and will fill up the better part of a corner easily, plus 30" x 50" is huge! Then you can put a Tri-Trap on top.

Somewhat unrelated - I have also been messing with filling coffee bags with Safe'n'Sound as I work in a coffee shop and get them free. They are not super pretty, but at 9'' deep in the corners, I think they work. It took a while to design something that holds its form well, and takes a bit of work. The bags alone are an odd size and shape for stacking.

Am I spending too much energy trying to reinvent the wheel? I love Cojo's DIY, but I need simple free standing solutions, and I don't have many tools.



Thanks for reading!!!!
Old 3rd August 2019
  #2
Here for the gear
 

Hey there! You guys are awesome. Theres so much knowledge here!

I am hoping someone can shed some light, or at least entertain the conversation. I can't tell if I'm proud, or embarrassed about how much I have thought about bass traps lately, and room acoustics in general. Polycylindrical diffusors made from drum shells anyone?

I know I'm noob here and everything, but the question of certain membranes reflecting frequencies above a certain point but allowing others below has to be legit. I know the census is you can wrap bags in thin plastic, but it makes the material less effective.

Does tightly wound fabric act like frk?

If air passing through a bass traps material is necessity, how can non porous material such as FRK be better?

I understand we want reflection in the highs, and mids with FRK facing out. But, if a non porous FRK panel still works at diminishing lows, is this due to reflections from the back wall, or does the low frequency content pass through the membrane?

I bet the low frequency waves move the FRK and the gas behind it.

If thats true, then there may be some value in thick cotton. If someone knows, and I'm waisting my time, please correct me. It's amazing how little on the web I can pull up about the subject, being that it seems like the easiest way to make low freq absorbers.

If no one really knows, than I'm def doing it, and recording the results so theres a thread about it here.

cheers!!!
Old 4th August 2019
  #3
Here for the gear
 

Looks like there is a -5dB attenuation of all frequencies, with an additional attenuation of frequencies above 2k. I’m assuming this will mean traps will be about -5dB less effective below 2k, and reflective above. That’s probably a big deal. Ha. The insulation was free, so that makes it a little less painful. The bags are 30” x 50”, so I’m hoping at the size, with lightly stuffed insulation they will help with the standing waves in my 9’ x 11.5’ room.

I’ll check the room with REW and a measurement mic when they are filled. Will let you all know. I know you all must be on the edge of your seat!

With wonder and excitement,
Jeffrey
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