"Airtight" bass traps why?

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jingleheimer

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Why exactly is it that sealing bass traps "airtight" is so important? Is it to stop sound spill or something else? Thanks for any help you can give me! -Jingleheimer-
 
Bass traps are often made of fiberglass or rockwool slabs,...

the fibers of which you don't want free floating in the air, as they may be harmful if you breathe them in. :eek:
 
The enclosure of the bass trap (mechanical) has to be sealed for it to work right.
 
If it is sealed, when the plywood face vibrates, it forces the air inside the trap to move into and out of the fiberglass panel inside, which dampens the vibrating plywood and soaks up the energy. If it was not airtight, the air would just move in and out the holes, and the plywood would not be dampened, so would just vibrate until it stopped on it's own (sending all that energy back into the room until it did).
 
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A Reel Person said:
the fibers of which you don't want free floating in the air, as they may be harmful if you breathe them in. :eek:
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Surely you could just cover both sides with fabric?
 
I was under the impression you could just use a thick broadband style absorber around 4-6" across the corner.
 
pandamonk said:
I was under the impression you could just use a thick broadband style absorber around 4-6" across the corner.
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You can, but the absorber is a sealed unit.
 
I think the discussion takes two turns in the road,...

as one "bass trap" would be mostly home made fiber "panels", and the ones needing to be "airtight" would be mechanical and/or manufactured specialty items.

;)
 
I edited my above post for clarity, and it refers to the mechanical type (pressure absorber) vs the fiber panels accross corners (velocity absorber). In the latter case, you wound not want it to be airtight, as the sound must pass into it to be absorbed.
 
Yeh. Got a fright, coz I've been giving Jingleheimer advice on his room setup, and suggeted he did the non airtight one. What is the acoutical difference. Surely the sealed absorbs more, but does the othre absorb a lot/enough? Surely it would with dense enough fiberglass. I suggested that he use them in the corners of the rooms for bass traps, and when recording vocals and drums he place them around them, along with the broadband absorbers i also suggested.
 
From what I've read, a home-made "broadband" absorber is a piece of rigid insulation wrapped in cloth. It is'nt tuned to a specific frequency therefore it absorbs frequencies ascross the entire range. A sealed trap is a wood frame with a plywood front and back (a sealed box) and has a piece of rigid insulation inside. The thickness of the front piece of plywood determines what frequencies will be absorbed. For example, if the front is very thin, all frequencies could be absorbed except the highs. I guess you would call that a bass/mid absorber. If the front is very thick, only low frequencies are absorbed and it would be called a bass absorber or trap.

Damn. I just skipped right over the question did'nt I. I don't exactly understand why it has to be sealed either.

I have read that filling the corners with rigid insulation is much more effective at absorbing than just putting rigid panels across the corner. When placing rigid panels on the wall, I wonder if it would be more effective to stack two panels rather than using one panel with an air gap.
 
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The broadband style ones can be used for many purposes, as they are easily manoverable. If all you need is bass absorbsion then the fixed ones are best, but if you want absorbsion of all frequencies the boradband across the corners is best. Am i on the right lines? And Jingleheimer, i think "broadband across corner" ones would probably be best.
 
Well the space behind helps it absorb. I've heard that a 1" piece 1" of the wall will act like a 2" piece. I've also heard that a 6" piece between a door frame with a 12' room behind has peak absorbion at 23Hz which is great if you have a doorway that doesn't need to isolate the sound from the room(which i will have woohoo:D)
 
pandamonk said:
I've also heard that a 6" piece between a door frame with a 12' room behind
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hey, that's a great tip pandamonk... i've got a room off the studio that is 10' deep and is isolated with the studio. i could make a door out of rigid panels and get some deep bass trapping.. nice. thanks...
 
:cool: I thought of it. And one of the guys from the building forum calculated it. Not sure if i was the first to think of it, but i ain't heard of it from anywhere else. I'm always coming up with stuff like this so look around for my posts. Heehee
 
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