Harder Corner

Build a 2' wide 8' tall frame, fill it with a pair of cloth covered 703 panels (2'x4") and mount the frame across the diagonal of the corner with the top and bottom left open. If you have any batts of fiberglass lying around tack one in the corner (tack the center of the back to the deepest part of the corner so it gets folded almost in half). Adjust the batt so that it doesn't stick out the top or hang out the bottom when you cover the corner with the frame.
Voila', a very efficient broadband absorber.
I covered some 703 in black burlap using pins and spray adhesive on the back side - bought it by the bolt at a fabric store - craft felt is also a pretty cheap way to go.
For the ceiling a light weight frame made of 2x2 lumber might be the easiest way to go.
The placement of an absorber device will effect its efficiency - for example, LF waves get folded up when they reach the room’s corners, and doubly so when they reach tri-corners [like where the floor or ceiling and two walls all come together]. A wide / thick panel of 703 mounted across the diagonal of a room corner from floor to ceiling will capture LF waves much better than the same panel mounted flush to the wall because: a) it has a large air gap behind it; and b) it covers a room corner and two tri-corners [one at the floor and one at the ceiling]. If the gap behind the front panels is filled with additional 703 [or even scraps of mineral fiber left from insulating the walls and ceiling] the device’s efficiency in the low part of the sound spectrum will be further enhanced. For a very clever approach to this design concept see:
Consider placement of broad band absorbers in the corners of the room whenever this is practical. The corners are locations where all the normal modes of a room will exist and absorbers placed here will have a chance to diminish all of the frequency components of a room’s reverberant field. Also absorbers in corners act on the pressures created by propagating sound waves more efficiently (just as speakers in the corner of room exhibit a boost in bass response). A panel of 703 placed across the diagonal of a corner from floor to ceiling (creating a variable depth cavity behind the panel) creates an excellent low cost broad band absorber.
Foam doesn't kill rooms; people kill rooms. :-)
'insert annoying trite saying'
> -----Original Message-----
> From: farmerbrown22002 [mailto:harder-sound@s...]
> Sent: Monday, December 01, 2003 9:46 AM
> To: acoustics@yahoogroups.com
> Subject: [acoustics] Corner trap question
> time to build in the control room corner traps and I have some very basic questions about dimensions and contruction that I have not found in the files section. As I understand it, these corner traps are broad band absorbers and not strickly a bass trap. To me this means that the out-word face has only (open weave) fabric between the room and the 703 that fills the corner. In other words, the trap is not air tight the way a true bass trap might be. Is this correct?
Yes... the idea is a wedge of absorptive material from floor to ceiling in the corner... you could build the thing entirely out of 703 and spray adhesive.
You might want to fill the hollow center with mineral wool [batts of R30 would do nicely].
> Secondly, how deep should they be? Commercial foam versions found here:
> Acoustical Solutions Alpha Corner
> are 12" deep. /Would there be any advantage to deeper traps? A potentially loaded question I admit, as the room itself and desired results of the listener might best dictate such things. But I thought I'd ask...
Deeper means it will work better lower in the band... a 4' wide [standard 2'x4' panels laid edgewise] wedge across the diagonal made of 6" 703 would not be overkill IMO... a 2' wide one made of 3" 703 would be a good compromise of cost & floor space lost vs. effectiveness low in the band.... also you could mix and match, for example: 2 footers in the front corners, 4 footers in the back corners with a large poly in the middle of the back wall.
> The front and rear of the room did have more low end energy with a kind of nul in the middle of the room for the same low frequencies (lets say below 100 hz). Will the corner traps effect/help this?
If you add four floor to ceiling corner mounted broadband absorbers large enough to work below 150 Hz to a small room [less 5,000 cubic feet], I would expect that there will be better LF clarity for all locations.