Diaphragm / Membrane Bass Traps - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 18 Old 04-02-14, 04:17 PM Thread Starter
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Diaphragm / Membrane Bass Traps

I have various questions about diaphragm resonators, but the first ones:



Is there a cheaper alternative to Mass Loaded Vinyl? What about PVC "closed cell expanded" sheets, dB-3 Acoustical Barrier @ Home Depot, or Torch Down Roofing?

If I put insulation in them, they'll give a moderately wide absorption band, right?

Can they be useful down to 16Hz?



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post #2 of 18 Old 04-02-14, 04:45 PM
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Some of those may work but nothing I know will get down to 16hz. The are by nature not broad spectrum devices but adding insulation to them widens the scope do which they cover. Again not by a lot if I recall maybe be a half octive each side of the peak.

One other thing your going to most likely need several of them to treat a issue not just 1 or 2.
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post #3 of 18 Old 04-02-14, 04:48 PM
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Re: Diaphragm / Membrane Bass Traps

Unless you want to go 36" thick, you'll be lucky to get to 30Hz.

The mass of the membrane, the thickness of the absorber, the density of the absorber all determine how low it will go and where it will cut of on the top end. For instance, FSK as a facing will start to cut maybe 600-700Hz. Pond liner - maybe 350. 1/2 lb MLV, about 250Hz

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post #4 of 18 Old 04-02-14, 05:14 PM Thread Starter
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Re: Diaphragm / Membrane Bass Traps

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Unless you want to go 36" thick, you'll be lucky to get to 30Hz.

The mass of the membrane, the thickness of the absorber, the density of the absorber all determine how low it will go and where it will cut of on the top end. For instance, FSK as a facing will start to cut maybe 600-700Hz. Pond liner - maybe 350. 1/2 lb MLV, about 250Hz
250Hz for 2lb MLV, perfect! A specific estimate

The other gent mentioned a half octave away from the peak, does that sound about right - below the target? i.e., if I target 40Hz, the resonator is only good to ~30?



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post #5 of 18 Old 04-02-14, 05:17 PM
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If I recall ruffly the box would be around 9 1/2 inches deep with 2lb limp mass on the front to hit 40hz I am at work so i will look later
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post #6 of 18 Old 04-02-14, 05:19 PM Thread Starter
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Re: Diaphragm / Membrane Bass Traps

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If I recall ruffly the box would be around 9 1/2 inches deep with 2lb limp mass on the front to hit 40hz I am at work so i will look later
Yeah, the excel file I'm using says 9.01" (internal), so - you're close.
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post #7 of 18 Old 04-02-14, 05:31 PM
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I have 2 rolls of 4x10 2lb limp mass sitting at hone that I still need to try one. The issue is getting it tuned just right which a lot of people have issues with. I would think using 8 2x2 traps would be a fairly good amount of traping but never got to building any yet.

When if ever my basement gets setup that is where they will go.
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post #8 of 18 Old 04-02-14, 05:46 PM
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Re: Diaphragm / Membrane Bass Traps

If you're building a sealed membrane then yes, it's more narrow in scope. If a limp unsealed membrane, then bottom up to X with X defined by the mass.

And the 250Hz was for 1/2 lb, not 2lb.

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post #9 of 18 Old 04-02-14, 06:21 PM Thread Starter
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Re: Diaphragm / Membrane Bass Traps

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If you're building a sealed membrane then yes, it's more narrow in scope. If a limp unsealed membrane, then bottom up to X with X defined by the mass.

And the 250Hz was for 1/2 lb, not 2lb.
Oops.

Any idea on the high Hz for 2lb?
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post #10 of 18 Old 04-03-14, 03:33 AM Thread Starter
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Re: Diaphragm / Membrane Bass Traps

Does any one know where I can get 4lb/ft2 membrane?

ALSO, can I build the box with varying depth? In other words:
The very center of the box would be deepest. The sides would be most narrow. (To fit snugly into a room's corner, while increasing depth.)

If so, I take the average depth and put that into a calculator, right?

Last edited by icor1031; 04-03-14 at 04:39 AM.
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