Acoustical Treatments Master Thread - Page 355 - AVS | Home Theater Discussions And Reviews
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post #10621 of 10631 Old 01-26-2015, 09:39 AM
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Originally Posted by myfipie View Post
Symmetry is most important from where you sit forward. If you have windows in one of those corners then use something that can free standing and stacked. Something along these lines.
http://www.gikacoustics.com/product/...fit-bass-trap/
For symmetry the best I can do is 1m worth of soffit traps or super chunks in all four corners but that is only 40% of the wall height covered. No idea how much effect that would have on the sound. Due to WAF I can forget about having traps blocking the windows. Padded curtains made from say duvets are ok though but would that be remotely similar to the soffit traps?

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post #10622 of 10631 Old 01-26-2015, 03:39 PM
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Originally Posted by granroth View Post
I recommend watching the Acoustics 101 and Acoustics 102 videos from Home Theater Geeks 177 and 178 with . They are absolutely the best intro to acoustics I've heard and, notably, they cover things like coverage levels very clearly.

http://twit.tv/show/home-theater-geeks/177
http://twit.tv/show/home-theater-geeks/178

(also available on YouTube)
Hadn't seen those before - thanks for sharing the links. Interesting absorb/diffuse pattern approach...

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post #10623 of 10631 Old 01-28-2015, 07:16 PM
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Soffit as partial bass trap

Let's say I'm building a soffit that wraps around my entire theater and mostly exists as a chase for HVAC ducts and wiring. In fact, the entirety of both sides and 3/4 of the back of the soffit are monopolized by the ductwork. That does leave a roughly 13' x 4' x 10" section of soffit above the stage that will have nothing practical in it.

So I'm thinking I can do double duty on that part and turn it into a bass trap by stuffing it with insulation. The question is "how"?

The soffit will be built with dual layers comprised of 5/8" OSB + 5/8" Drywall (since most of it is to hide possibly noise HVAC). I'm assuming that that will also effectively reduce the "bass trap" ability of the soffit to unmeasurable levels.

If that's true, then that implies that I will need a hole in my soffit? Maybe covered with fabric?

If so, then how big should said hole be, to be an effective bass trap?

Just pink fluffy stuffing, or would it really help to use rigid fiberglass?
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post #10624 of 10631 Old Yesterday, 07:36 AM
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I would not use holes, but cover it with fabric, keeping it open on all sides facing the room. And yes use normal fluffy fiberglass.

Glenn Kuras
GIK Acoustics

http://www.gikacoustics.com

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post #10625 of 10631 Old Yesterday, 04:29 PM
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Originally Posted by myfipie View Post
I would not use holes, but cover it with fabric, keeping it open on all sides facing the room. And yes use normal fluffy fiberglass.
So this is roughly what it'll look like (minus the light tray):



The grey part is entirely taken up by ductwork (in fact, 3/4 of it is the duct) so only the green part is available to be a bass trap.

Are you suggesting to essentially have no bottom and no side to the green part of the soffit (other than the frame) and to install just have fabric covering the frame and fiberglass?
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post #10626 of 10631 Old Today, 12:37 PM
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Any suggestions for how to treat a 31.5Hz room mode? It shows in my REW measurements as a null (i.e. not a hump). It's very narrow so it's not a cause for major concern.

I played with the PEQ on my Dayton SA1000 equivalent but boosting did nothing but make other frequencies worse. Cutting didn't seem to have any effect whatsoever.
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post #10627 of 10631 Old Today, 03:24 PM
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31.5 Hz will most likely be a first order length mode resonance in most rooms. Your whole room rings like a tuning fork at that frequency, so there is a LOT of energy built up in that resonance. Absorbing the energy with a velocity based absorber will prove disappointing, I'm afraid.

You are probably best served by first relocating your sub(s) or adding a second. If you can't make that work, for whatever reason, I'd say you need to be looking into a resonant trap solution.
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post #10628 of 10631 Unread Today, 07:07 PM
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At 31.5 there is limited music content. You wont notice the null during playback I think.

In either case, multiple subs is most obvious way to help this problem with reasonable certainty.

Just moving one sub around will often just create different peaks and nulls. Tuning options and permutations increase a lot with multiple subs.
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post #10629 of 10631 Unread Today, 07:25 PM
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Originally Posted by HopefulFred View Post
31.5 Hz will most likely be a first order length mode resonance in most rooms. Your whole room rings like a tuning fork at that frequency, so there is a LOT of energy built up in that resonance. Absorbing the energy with a velocity based absorber will prove disappointing, I'm afraid.

You are probably best served by first relocating your sub(s) or adding a second. If you can't make that work, for whatever reason, I'd say you need to be looking into a resonant trap solution.
Well, I have 4 subs and I've located them in all kinds of places. I believe for that mode the only placement that addresses the problem is dead center in the room.

I've attached the REW measure just for the subs. It's unsmoothed and without any EQ (I don't have access to any). Looking at it in conjunction with the L main it doesn't look so bad.

According to a calculator I googled I'd need a 9ft gap behind an absorber! Seems a bit much.

Does a tube trap count as a resonant trap? Or are they something else? Is there a DIY I can follow to see if I can make a dent in it?

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post #10630 of 10631 Unread Today, 07:29 PM
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A tube trap is the sort of trap that might help, but they are tough to build and tune and you may need several.

Have you tried adjusting phase, polarity, or delay of some of your subs? I'd start by inverting the polarity of the subs in one half (either front or rear) of the room.
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post #10631 of 10631 Unread Today, 07:42 PM
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Originally Posted by HopefulFred View Post
A tube trap is the sort of trap that might help, but they are tough to build and tune and you may need several.

Have you tried adjusting phase, polarity, or delay of some of your subs? I'd start by inverting the polarity of the subs in one half (either front or rear) of the room.
Yeah, I did that. Continuous phase, 0-180 switch level, whatever the sub supported. It was a lot worse before. I have no way to control delay at the moment.

I do have a MiniDSP 2x4 that I've tried once or twice that never does what I expect/want. As a splitter it was awesome.
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