Acoustics of corners

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With all room shapes, there will be modes. My question is : why do some acousticians and books recommend corner placement of basstraps or absorbents ?

Hi jlo :)

From my experience, the corner allows absorption of not only axial modes (1,0,0 mode) but is also helps with absorption of tangential and oblique modes which will also have pressure maxima at the boundary.

If, for example, you place your trap in the centre of a wall, you would attenuate the axial mode, but the modes of the perpendicular opposing walls, corner to corner modes and other exotic mode shapes would be unaffected.

Hope this helps.

Andy
 
Hope this helps. Andy

Acoustic Absorbers and Diffusers third edition by Peter D'Antonio and Trevor Cox.

Sorry guys, but this litterature I know : it explains nothing at all about efficiency of absorption in corners. As I already told, the only beginning of an explanation was proposed by Earl Geddes and it is far from the standard model for room modes.
 
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I have used absorbers across corners. Lots of them. They do make some difference. I used corners to minimise the room space they used and still they were very intrusive. On the other hand the multiple sub approach can present an effective active absorber scenario.
 
Hanging a dead wall over an existing wall is not too hard and much more effective. Takes up almost zero space. Not as easy as just buying traps and placing them in corners.

What is your favorite recipe for a dead wall?

My rooms problem is that it's dry wall walls with Armstrong acoustic tile ceiling. The ceiling is too dead for midbass and too lively above. So it looses lots of midbass energy while maintaining flutter. I don't have the heart to tear down and replace the ceiling. I use duct board to affectively attenuate flutter which leaves the midbass much too dead.

Thanks!!

Scott
 
@Scott
You mean other than multiple subs?

Yes, I have two subs now and deep bass is fine, my troubles are midbass 80-200hz.

I think the only solution for it is to replace the ceiling or add large surface diffusion which would equate to replacing the walls. For now I use a different room. We have a semi open floor living room I like better but others like to watch TV while I listen and that causes other problems.

Can't win.

My personal favorite sounding space is a small clearing in a wooded lot. No echo what so ever. A $1000 system sounds like a million bucks. LOL
 
Can. I'm not saying it's easy tracking down issues in the lower midrange, it's probably the most difficult. Very important to good sound as well. That tactile feel and all.

Any idea whether the modes in question are whole room connected or mostly single wall reflections?

I'm going to say whole room. Also it's a stick and drywall room within a concrete room. With concrete floor. Double yuck. I should just repurpose the bad room and utilize an upstairs room by creating good diffusion.
 
What is your favorite recipe for a dead wall?

Scott

Hang two sheets of drywall on resilient channel and glue them together with a non-hardening damped glue, i.e. constrained layer damping. They must float so seal the edges with a soft material. (And no shorting screws please! I screw the layers together until the glue dries and then remove them.) These large panels will be great LF absorbers. Also remember that at LFs it is only necessary to dampen on of any two opposing surfaces. One wall acts exactly the same as two walls in the modal region.
 
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This comes close and is more practical DP_woofer_room
I don't know what this means..
Thus, such a configuration should therefore yield bass response which sounds subjectively similar to dipole
..and I don't much go for the idea of dipoles exciting less modes, and even 'if' they did, the goal is the same and why try to avoid what has to be done?
 
Hang two sheets of drywall on resilient channel and glue them together with a non-hardening damped glue, i.e. constrained layer damping. They must float so seal the edges with a soft material. (And no shorting screws please! I screw the layers together until the glue dries and then remove them.) These large panels will be great LF absorbers. Also remember that at LFs it is only necessary to dampen on of any two opposing surfaces. One wall acts exactly the same as two walls in the modal region.

Dr.Geddes,
let's say I have this room 24'x16'x10', all concrete and brickwalls.
What is the size of the hanging drywall panels (long wall and short wall) in order to be effective ? Can I hang let's say three panels on a wall to reach the needed area ?
thanks in advance
 
Dr.Geddes,
let's say I have this room 24'x16'x10', all concrete and brickwalls.
What is the size of the hanging drywall panels (long wall and short wall) in order to be effective ? Can I hang let's say three panels on a wall to reach the needed area ?
thanks in advance

Obviously the larger the panels the more absorption you are going to get and at an ever lower frequency. How large they are is up to you. An all concrete room with no leakage would need, IMO, at least one of every opposing pair of walls at least 75% covered.
 
Yes, I think in practice it probably is. Theoretically in a perfectly symmetrical room it would mean no room modes. This comes close and is more practical DP_woofer_room

John's approach is easy and does help the modal situation in a small room, but it is still not optimum. Letting the frequency response and phase of each woofer be a variable will yield better results. However, this technique requires measurements and some sense of what you are doing, but I have described how to do this many times.

And I agree with Allen above when he said that looking at cancelling modes is not the way to approach the problem. You don't want to cancel the mode, you just want to tame it.
 
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