My Experiment with a Metal Panel Absorber


My Experiment with a Metal Panel Absorber

I built this a few weeks ago, but at the time, the guy I built it for didn't want me to share the the details... Finally managed to convince him... The room was a tiny 11' 6" x 8' 6" x 9' 6". For various reasons, I decided to go with one large 4' x 8' trap with a 1 mm steel sheet. At the time, I was not able to source Basotect, so I went with open cell PU form of 24 Kg/m3. Thing is... I couldn't take the risk of of the sheet falling... serious risk to life and gear. So heres what I did... I took 2 nos. 8' x 4' x .75" sheets of plywood and nailed them together to create a boundary of as much mass as I could afford. I then put a 6" deep frame around it and vented the middle 2". I sourced the spray glue that the guy in the hardware shop recommended, and the machine to spray the glue was hired. 6" of the PU foam was stuck to the aforementioned double layer of plywood and the steel sheet was stuck on the foam. Then a beading was nailed in all around the frame... as such, the beading was not touching the metal sheet... but I don't know really if the steel sheet has come unglued and is now resting on the beading. I put the speaker (Sonodyne 8") in one corner and the trap on the other side of the room, in three positions... against the wall, on the floor, and diagonally, between the wall and the floor. I measured in 5 positions around the "sweet spot"... 38% from the front wall I know is pretty arbitrary... but it was what made sense in the room, anyway... The most encouraging result is with the trap against the wall... which has reduced the decay time @ 50 Hz from ~1750 ms to ~730 ms. 50 Hz corresponds with the length of the room (11' 6"). With the trap placed diagonally, the mode has moved up by a few Hz, this is almost certainly because the trap has significantly reduced the length of the room... Anyway, the pics below should give us a clue of what the traps are doing. What would I do differently, if I were to do it again? * Get rid of the frame, but for this, I'd have to be confident that the metal panel will not come unglued. * Use a 2.5 mm steel sheet, which is far more effective around 50 Hz. * Reduce the thickness of the foam from 6" to 4", so I can get that much closer to the wall... In this case, I used 6", so that I could put a frame around it and still be able to vent 2" in the middle... * Test using corners only... mic, speaker and trap. This is what G.E. did, and I think it is the better way...

Let me know what you guys think...

Attached Thumbnails
My Experiment with a Metal Panel Absorber-empty-room.jpg   My Experiment with a Metal Panel Absorber-trap-against-wall.jpg   My Experiment with a Metal Panel Absorber-trap-diagonal.jpg   My Experiment with a Metal Panel Absorber-trap-floor.jpg   My Experiment with a Metal Panel Absorber-my-vpr.jpg