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I am currently using "egg carton" foam on my walls at the first reflection point, but notice that the soundstage seems dead at the edges. Do I want something that will absorb, diffuse or both? What products should I look at? Thanks!
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I agree with others. I've found foam absorption to work best at first reflection points. I've had great luck with Sonex 3" foam. I agree that 2" is generally not thick enough (although I've found it useful as a "supplement" in other places in the room (further from my listening area). One important thing I've learned: the concave Sonex is much more linear in it's effect than the convex. I don't know why this is, but it's unmistakable in my situation. I wish it weren't so, because it means buying more boxes of Sonex, i.e. because I'm only using half of it. I guess if I were to do this again, I would call Sonex and ask them if they could supply only the concave. Good luck.
to take a look to some very interesting articles at www.gikacoustic.com and www.realtraps.com and other similar websites, the more you read and learn about, the better you'll prepare your criteria to make a proper decision. Of course the proof is always in the pudding (listening) after which you'll have a complete, experienced opinion coming from your own system, speakers, room and tastes. "Absorbtion/diffusion" is an interesting and extensive subject. Best, Antonio Machado.
David is right, difusion needs room to work, absorption at the 1st reflection points is what is best for most rooms.However, you say you are using "egg crate" foam, but give no other details.
How thick is the foam overall (tip of 'egge' to rear flat surface)?
If it is not much more than 2" or so, this may be a part of the problem, as then it means that the absorption is not occuring at lower frequencies.The other side of the problem is having an area that is too large with the thickness too thin. A wall panel for absorbing the 1st reflection should be approx. 30-36" wide and about 48" tall. If your foam is larger than that, and not thick enoug, this could cause a problem for the imaging.
Finally, if it is foam that is not designed for acoustics use, such as the type intended for use as a bed mattress pad, then it may be reflecting more of the upper midrange and lower treble than a good grade of acoustic foam (or fiberglass) would. This could also be a cause of imaging problems. You might be able to "fix" this by adding a layer of polyester batting over the front surface of the foam. The 1/2" to 3/4" thick hi-loft type is what you would want to get.
> Do I want something that will absorb, diffuse or both? <I'm with David - absorption is the better choice for first reflection points. Diffusion can be useful in larger rooms on the rear (or front) wall, but it's more icing on the cake compared to the staple of absorption. Also, good diffusors are complicated to make and thus cost more than good absorbers. The thin cheap diffusors I've heard are not very useful IMO.
When you treat first reflection points, the aim is to reduce the level of the early reflections reaching your ear so that the direct sound is more dominant. Both absorption and diffusion will do that, but there are differences.Diffusion takes time in which to develop. Diffusion spreads the soundwaves over a larger area and the amount of reduction you get is proportional to the increase in area over which the soundwave is spread at the plane at which you make the measurement. Sit close to a diffusor and there is little reduction in the level of the reflection because the reflection hasn't yet had much space in which to spread out. Diffusors are more effective the further away you sit.
Because of that my preference is to use absorption at early reflection points because it will have a bigger impact on the reflections. I use diffusion further away at other locations where the sound being diffused will have more space in which to diffuse before reaching me, and ensuring that most of the diffused sound reaching me will have been reflected at least one more time as well.
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