#1840831 - 11/14/07 08:17 AM
Making a whole wall out of traps?
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Msquared
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Registered: 11/14/07
Posts: 4
Loc: St. Louis, Missouri, USA
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I’ve moved into a home with a basement. About half of it is finished as two sort of separate rooms, and the other half is unfinished storage. The rectangular half that is to be the A/V area is oriented in the following way as you would sit facing the TV and speakers: right and back walls are exterior walls finished with drywall and insulation, the left wall is sort of an island/bar/pass-through that doesn’t present a completed boundary, and the wall behind the speakers is currently metal studs with drywall and with unfinished space behind it. The room dimensions as currently laid out are 20’9”l X 12’7”w X 6’8”h. The room on the other side of the island/bar adds another 15’3”, but it’s probably only partially “seen” by the sound waves. All of this finished area has carpet and padding over the concrete floor. The unfinished space behind the front wall is 23”8’l X 27’11”w, and of course right now it is closed off from the sound (more or less). I know none of this is ideal, but my system actually sounded overall pretty good in it as currently laid out. I need to re-do the wall behind the speakers at this time anyway, and so I need to concentrate on my opportunities to improve sonics with that wall for now..
So I can build this wall out of whatever I want, and it could be 1’ or 2’ thick if needed. And I don’t care about soundproofing the room from the unfinished floor space behind it. I am pretty sure that the flimsy sheet-metal studs with just drywall is a terrible way to do things, unless it just happens to be acting as a good resonant bass attenuator. I thought about making a whole wall out of studs on 24” centers and some thickness of 703 insulation or other absorptive materials, and with no solid wall surface on either side – IOW, make the whole wall an absorptive trap. This could allow some absorption of bass notes as they pass from the listening room into the unfinished space; and would also further attenuate those notes when they reflect back from the unfinished room. It could sort of end up as an infinitely deep room as far as bass notes are concerned (correct me if that’s wrong, though). That could support any bass I ever try to reproduce there, plus make it interact less with the other two dimensions’ room modes and therefore reduce reinforcements and cancellations in the bass range (I think). Does this theory sound plausible?
I guess another way of asking this is: If I'm rebuilding an interior wall that would get traps on it anyway; and I don't need to soundproof the listening space from the space on the other side of the wall; then do I really need a wall material at all or can the traps serve as the wall itself?
PS – I also thought about making the wall transparent to bass waves, I could effectively have a ???? long room dimension, with the speakers more than halfway out into the room. But that won’t actually eliminate bass modes – I think it would just delay them and spread them out so that sweet spots would be larger and easier to sit in. Not a bad result, but not as good as an infinitely long front room dimension.
PPS – I would eventually do further treatments on other walls, concentrating on the two back corners and the right side (exterior) wall. Ethan Winer’s 3-part traps seem like a good way to go for this.
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#1840936 - 11/14/07 11:28 AM
Re: Making a whole wall out of traps?
[Re: Msquared]
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Ethan Winer
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Registered: 06/12/00
Posts: 5300
Loc: New Milford, CT, USA
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First, I wouldn't try to use my wood panel bass traps that way. But your general idea of a "wall that traps bass" is not bad. If you have plenty of space, I'd make it at least four inches thick with 703 or 705, or 12 inches thick with fluffy fiberglass. However, I have to admit I've never done this so I can't guarantee that it will work as well as more conventional trap placements. 
--Ethan
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#1841127 - 11/14/07 05:24 PM
Re: Making a whole wall out of traps?
[Re: Ethan Winer]
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Msquared
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Registered: 11/14/07
Posts: 4
Loc: St. Louis, Missouri, USA
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Ethan, thanks for your response. Right, I wasn't really thinking about the wood panel traps for this wall - just absorption panel as you recommend (however, I will definitely make your traps part of my long-term plans for the other two solid walls). I think I'm going to give this a shot. I wish I had a better baseline reference so I could report back with measurable results. But I'll try to take some pics and post them here, at the very least.
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#1895887 - 02/21/08 08:00 PM
Re: Making a whole wall out of traps?
[Re: Msquared]
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Msquared
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Registered: 11/14/07
Posts: 4
Loc: St. Louis, Missouri, USA
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Okay, I'm finally getting around working on this project, and I'm bringing it back to the top to ask more questions. This isn't a huge wall, and so costs won't get out of hand no matter which materials I use for damping. Staying within reason, I could go as thick as 12" of 703 (layering six 2" sheets together), or any smaller thickness of it. I can also use mineral wool in the same range of total thicknesses, but I can't find a good set of absorption coefficients (across the full range of frequencies) and therefore don't know how it compares to 703 at any given thickness. Finally, I could certainly use the fluffy fiberglass bats, and I could go with 12" uncompressed (which gives less absorption, right?) or even 24" compressed into a 12" trap thickness (or whatever). That seems like more work to build, but if it had some advantage I'd do it.
So with all of that said, if you could choose among any of these materials for two sections of wall roughly 25sqft each, which would you choose and why? Thanks.
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#1896166 - 02/22/08 08:04 AM
Re: Making a whole wall out of traps?
[Re: Msquared]
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Ethan Winer
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Registered: 06/12/00
Posts: 5300
Loc: New Milford, CT, USA
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As fiberglass is made thicker you can get away with lower density for the same results. By the time you get to 12 inches thick the fluffy stuff works very well. And of course it costs a lot less. So if you have 12 inches to play with I'd use 12 inch thick fluffy fiberglass squeezed down to 10 inches, then put 2 inch 703 or 705 in front of that to make a clean flat front surface.
--Ethan
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#1896182 - 02/22/08 08:30 AM
Re: Making a whole wall out of traps?
[Re: Ethan Winer]
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gullfo
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Registered: 03/30/04
Posts: 75
Loc: Old Tappan, NJ, USA
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also. consider leaving some space in the wall in case you do need some panel traps - you can then put them in place on the boundary wall behind the porous absorption and get the benefits of both.
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#1896677 - 02/22/08 09:45 PM
Re: Making a whole wall out of traps?
[Re: gullfo]
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Msquared
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Registered: 11/14/07
Posts: 4
Loc: St. Louis, Missouri, USA
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Ethan, that sounds like a very good plan. It hadn't even occurred to me to mix the absorption media. Gulfo, the area behind the wall is just more basement space, but unfinished. I could certainly add panel traps at any time. I hadn't thought of that either, but will definitely keep it in mind. Thank you both for your suggestions!
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