DAX616 Posted August 24, 2004 Share Posted August 24, 2004 Will bass trapping behind the wall help cancel room modes? I have a framed wall in front of my basement concrete wall and wish to hide bass trapping.Is the framed wall the point where my bass starts the mode or is it the more substantial foundation wall. The distance is about 15 " from the framed wall to the concrete wall. Quote Link to comment Share on other sites More sharing options...
DrWho Posted August 24, 2004 Share Posted August 24, 2004 Of what is the framed wall constructed and what kind of trapping were you thinking of doing? The reason for room nodes is that the sounds (bass) gets reflected back into the room where all sorts of phase issues start happening (aka, room nodes). Any kind of wall is going to produce some level of reflection, some level of absorbtion, and will allow some level of sound to through. A bass trap behind a wall is only going to absorb the sounds that have managed to go through the wall...and then, the rest of the sound that doesn't get absorbed is going to have to go through the wall again and be even further reduced in volume. (kinda defeats the purpose of a bass trap behind the wall because the sound coming back out from hitting the concrete is already getting atenuated twice and is much lower in magnitude in comparison to the sound being reflected off the first wall). If it is at all possible, you could try cutting holes in your wall where you notice bass building up and then cover the holes with an acoustically transparent "wall" and then place some bass trapping behind there...This would basically result in changing the shape of the back wall and then adding some trapping in the new corners. There are also "slot resonaters" that could very easily be built into your 15" space that would only require small openings (slots) in your framed wall. I wouldn't be able to tell you how to make one though. If you want to go real insane, I might suggest making the whole wall a fake wall and then manipulate the space behind to act as a giant diffuser (or a few big diffusers) and then use bass traps in the corners...maybe even extending the bass traps a little further into the room. The good ones that attenuate very low frequencies extend 24" along the sides (which would mean that you'd have something sticking out 9" along the side of your wall). Btw, it wouldn't hurt to know the current dimensions of your room (length, width, AND height), as well as what issues with the bass you're experiencing (if you don't hear any problems, then there's no point in "treating" the room). And while you're at it, what kind of equipment are you using and where is it located? Anyways, to give you a simple answer to your question...No, trapping behind a "normal wall" will have no effect on room nodes. Quote Link to comment Share on other sites More sharing options...
Colin Posted August 24, 2004 Share Posted August 24, 2004 umm, adding insulation behind a wall has no effect on room reflections? is this only one wall in the basement? Quote Link to comment Share on other sites More sharing options...
DrWho Posted August 24, 2004 Share Posted August 24, 2004 ---------------- On 8/24/2004 6:16:47 PM Colin wrote: umm, adding insulation behind a wall has no effect on room reflections? ---------------- Wait does it? I don't think it would... Quote Link to comment Share on other sites More sharing options...
DAX616 Posted August 25, 2004 Author Share Posted August 25, 2004 Thanks for your input. I checked with aurelex about this subject. They did not recommend it.I would say just thinking about it,the parallel walls act like a tuning fork. The bass will vibrate the less massive framing walls before it will the foundation wall. Therefore the framing walls contribute to the frequency response of the room more than the boundary described by the foundation wall.The framing wall when vibrated by a frequency does not accurately reproduce that frequency.So if I have a calculated mode @ some frequency because of my room size. The response of my room may be differ from this result.I have framing up in my basement and will begin wiring soon. The layout is probably unconventional but I will stive for symmetry. Basically the room is about 29' x 27'x 8' with hard floors. Klipschorns in bricked corners along the long wall, between the speakers will be thick velour curtains covering two sliding glass patio doors. To the rear of the listening position (middle of the room) will be a polycylinder array centered in the room about 8' lng I have no real equipment yet.I will test the accoustics of the room first after it is built .The side walls and ceiling will be spot treated.Since there is quite a bit of witchcraft in accoustics I will try to solve this problem empirically. Correct me if I wrong. Quote Link to comment Share on other sites More sharing options...
artto Posted August 25, 2004 Share Posted August 25, 2004 Bass traps are often built into the walls and ceilings of recording studios. The depth required for them to be effective is usually quite substantial. You need at least ¼ wavelength of the lowest frequency to be effective. At 16 Hz, this is 17.5. At 32Hz this is 8.75. As Mike (DrWho) mentioned, the interior wall surface needs to be acoustically transparent, or at the very least, somewhat resilient, with the absorption material behind it able to damp any vibration motion. For the most part, the traps must be in the room to help. Use of fiberglass insulation in the 15 space between the interior wall and the concrete wall will help damp any resonances in that space. It will not have much, if any affect, on room reflections at most any frequency. The main interior wall surface is usually sufficiently rigid to reflect all frequencies to some extent, obviously longer wavelengths of bass, to a lesser extent. However 15 is not much different than the difference between a 32Hz and a 33Hz tone. The 15 space behind the wall approximately relates to ¼ wavelength of a 225Hz tone or the full wavelength of a 900Hz tone, clearly out side of the bass range. Quote Link to comment Share on other sites More sharing options...
Colin Posted August 25, 2004 Share Posted August 25, 2004 "The 15 space behind the wall approximately relates to ¼ wavelength of a 225Hz tone or the full wavelength of a 900Hz tone, clearly out side of the bass range." oh, so the insulation behind the walls only affects the upper bass (225Hz) and the critical MID-RANGE (900Hz)! gee, guess it might make a big difference after all - in fact, too much wall insulation might dampen the mid-range... Quote Link to comment Share on other sites More sharing options...
DAX616 Posted August 25, 2004 Author Share Posted August 25, 2004 Given the wall is drywall and framed,(not accoustically transparent)if any trapping occurrs in that space it will be of the third order. Most of the "reflection" or response in that range of frequency occurrs inside the room. The upper bass, critical mid range behave in a transient fashion kinda specular and kinda wave like.I believe insulation will dampen resonances between the hard surface of the concrete wall and the framed wall, but the cavity behind is not sealed and any resonance should be short lived because of the difference in densities. Am I correct to think this way? Quote Link to comment Share on other sites More sharing options...
Rudy81 Posted August 25, 2004 Share Posted August 25, 2004 If you have a large space behind the wall, as you indicate, it is the perfect space for a Helmholtz Resonator. Get a copy of "Acoustic Techniques for Home & Studio" by F. Alton Everest. It will have more information on this and other acoustic subjects than you can use. It will disucss this type of bass trap. Quote Link to comment Share on other sites More sharing options...
DAX616 Posted August 25, 2004 Author Share Posted August 25, 2004 I have this book and reccomemnd it as well. I am of the mind that broad band absorption or basic diffusion is safest, because I cannot accurately measure the room response at this point.It is my understanding that hemholtz resonators target a specific frequency and the "Q" is how efficiently it does so. I believe Artto preaches braod band absorption, possibly for this reason.Thanks for the referral. Quote Link to comment Share on other sites More sharing options...
artto Posted August 25, 2004 Share Posted August 25, 2004 ---------------- On 8/25/2004 9:35:20 AM Colin wrote: "The 15” space behind the wall approximately relates to ¼ wavelength of a 225Hz tone or the full wavelength of a 900Hz tone, clearly out side of the bass range." oh, so the insulation behind the walls only affects the upper bass (225Hz) and the critical MID-RANGE (900Hz)! gee, guess it might make a big difference after all - in fact, too much wall insulation might dampen the mid-range... ---------------- I DID NOT say that insulation (or too much wall insulation) in that 15" wall cavity (or any wall cavity for that matter) might dampen the mid-range. What I did say was that the 15" cavity behind the solid interior wall would not be very useful as a bass trap, its too small, even if filled with insulation. Even designed as a hemholtz resonator it would have limited bandwidth. (and BTW, I really, really resent anyone putting words in my mouth, or even implying that "such and such" is what I said) Quote Link to comment Share on other sites More sharing options...
artto Posted August 25, 2004 Share Posted August 25, 2004 ---------------- On 8/25/2004 10:33:40 AM DAX616 wrote: Given the wall is drywall and framed,(not accoustically transparent)if any trapping occurrs in that space it will be of the third order. Most of the "reflection" or response in that range of frequency occurrs inside the room. The upper bass, critical mid range behave in a transient fashion kinda specular and kinda wave like.I believe insulation will dampen resonances between the hard surface of the concrete wall and the framed wall, but the cavity behind is not sealed and any resonance should be short lived because of the difference in densities. Am I correct to think this way? ---------------- correct Quote Link to comment Share on other sites More sharing options...
DAX616 Posted August 26, 2004 Author Share Posted August 26, 2004 No offense Artto. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.