I was wondering what the absorbtion coefficient is for 4" thick oc 703, I have two bass traps in my room where the rear wall meets the ceiling, I can't hear much bass response from my monitors with commercial mixes I am familiar with elsewhere(I'm guessing due to cancellation) and was wondering whether or not it was worth building more bass traps with 4 ply 1" thick 703(I have 12 pcs of 703 left)as I only need absorbtion from around 200 all the way down, also where is the absolute crucial place to hang these for low end absorbtion, as I am only concerned with the sound at the mix position
4" thick 703 question/low end bass absorbtion
- Thread starter Davidblais
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Thanks that was helpful, however all this rave about rigid fiberglass, 4 inch thick 703 has a acf of .84 at 125hz, and the auralex Venus traps have a acf of 1.19 at 100hz, why does everyone favor rigid fiberglass for low end absorbtion if the foam corner traps are more effective? Should I have just bought those instead of all that material an labor, as those traps are affordable?
i'd get somebody who knows how to do the math on your room to determine the room nodes which you are dealing with and to predict where they are relative to your listening position. if you hear no bass it's likely a room dimension problem and adding 703 cannot do anything to help that. 703 can knock down a peak somewhat but will not treat a suckout. that would require some sort of DSP or EQ....or move your listening position maybe.
i just removed a huge amount of 1" and 2" 703 from my room because i had too much absorbtion.
but no matter i still had a suck out around 25hz-31hz at my listening position that there was not much i could do about. my speakers have adjustability in the bass output and i was able to reduce the suckout by 50%. but to do that i needed to understand cause and effect.
i just removed a huge amount of 1" and 2" 703 from my room because i had too much absorbtion.
but no matter i still had a suck out around 25hz-31hz at my listening position that there was not much i could do about. my speakers have adjustability in the bass output and i was able to reduce the suckout by 50%. but to do that i needed to understand cause and effect.
Mounted in a corner the effective path length is increased and absorption goes up due to te rear absorption (vs. flat on a wall). Fiberboard panels are cheap and easy to use; I am not sure anybody has said foam traps are ineffective (caveat: I have stated before that Auralex LENRD's do not impress me -- see their specs, not much LF absorption). Good corner traps work well, but most of the sites sell panels and so that's what we get. Whatever you get, there has to be enough material to reach (or at least closely approach) the 1/4-wavelength of the sound you want to absorb to do much good. That is,
fc ~ v/4t where fc is the low-frequency cut-off, v is the velocity of sound (1127 ft/s), and t is the effective thickness of the absorber (in ft if v is in ft/s)
The effective thickness is equal to the actual thickness for sound coming straight at a panel mounted flat on a wall; for most real situations the sound is oblique and the panel is a bit off the wall so the effective path length (t) is longer and fc is lower. Ethan's site has a lot of helpful info worth reading: www.realtraps.com There is also a room mode calculator on his site.
If you are sitting in a room modal null ("suckout") absorbers will not help much because it is due to signals cancelling at that point. In fact, short of absolutely killing any reflections at that frequency (very challenging in the bass region), about all you can do is move the listening spot to get out of the null. EQ can generally reduce a peak, but a null is tougher to deal with and EQ alone generally won't do it.
You can make your own corner traps out of the fiberboard; one way is to e.g. place a 2' x 4' x 4" (or 6") panel in the corner with another half-width panel behind. The back panel can also be thicker, e.g. 6", since there is room behind the corner panel. Another way is to cut the fiberboard into triangles (maybe 24" - 36" on a side depending upon what you have room for) and stack the triangles (lying flat) in the corner from floor to ceiling; that would likely beat most any typical corner trap.
HTH - Don
fc ~ v/4t where fc is the low-frequency cut-off, v is the velocity of sound (1127 ft/s), and t is the effective thickness of the absorber (in ft if v is in ft/s)
The effective thickness is equal to the actual thickness for sound coming straight at a panel mounted flat on a wall; for most real situations the sound is oblique and the panel is a bit off the wall so the effective path length (t) is longer and fc is lower. Ethan's site has a lot of helpful info worth reading: www.realtraps.com There is also a room mode calculator on his site.
If you are sitting in a room modal null ("suckout") absorbers will not help much because it is due to signals cancelling at that point. In fact, short of absolutely killing any reflections at that frequency (very challenging in the bass region), about all you can do is move the listening spot to get out of the null. EQ can generally reduce a peak, but a null is tougher to deal with and EQ alone generally won't do it.
You can make your own corner traps out of the fiberboard; one way is to e.g. place a 2' x 4' x 4" (or 6") panel in the corner with another half-width panel behind. The back panel can also be thicker, e.g. 6", since there is room behind the corner panel. Another way is to cut the fiberboard into triangles (maybe 24" - 36" on a side depending upon what you have room for) and stack the triangles (lying flat) in the corner from floor to ceiling; that would likely beat most any typical corner trap.
HTH - Don
The actually not, they have cutouts yielding a thickness range from 6 to 10" thick, the dimension from the corner of the wall out ward measures 12 inches, but that "thickness" is only about 1/8th of an inch wide, but based on what I've read I got the impression those weren't real bass traps
If you own a rectangular room I can recommend the excellent online calculator at
http://www.hunecke.de/en/calculators/room-eigenmodes.html
The shadowed information of the pressure intensity of each frequency helps a lot for positioning you and the speakers
This whole site is one best I ever found in the net about room acoustics.
http://www.hunecke.de
The suckout is the result of superimposing a positive wavefront/reflection with a negative wavefront at the same point in space. The sum of + and - is a lack of pressure. Standing waves keeps repeating the same back and forth movement, so they appear to us (listeners) as regions in the room with high and low pressure. Dealing with a suckout is no different than dealing with a boom - the reflection needs to be tamed either at the boundary or somewhere along the path they travel in the room. EQ won't to anything at all about the energy level in the reflections.. It may send less energy into the room at certain frequencies, but it can't alter the level of the reflections themselves.
I don't doubt the results you observed. Porous absorbers aren't much effective at such low frequencies. Try tuned traps to treat that area!
These can be had at various target frequency ranges below 100Hz:
http://www.rpginc.com/products/modexplate/index.htm
http://www.rpginc.com/products/modexcorner/index.htm
Regards,
Andreas Nordenstam
Very interesting! Would I be correct in thinking that the dark areas on the images produced (especially near the walls) are the places which would be the most beneficial places to put bass traps? (I see a lot of dark in corners and I remember Ethan and co's advice about bass trapping in corners.)
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