Originally posted by Dennis ErskineAn anechoic chamber is all absorption (ever done research in one?). Like this one for example:
Sound decays (STP in air) at the rate of 1/r squared. The rate of decay is not affected by reflection (a form of diffusion). It is affected by distance and absorption.
The purpose of diffusion is to randomize reflections which will result in axial, tangential and oblique reflections.
Learn something every day. I always thought the wedges were all edge hardened in those chambers so they acted more like diffusors. Guess I will have to stand corrected on that one.
My comments were only made to present the poster with options, not to rebutt any other previous statements. They were also stated understanding that I was trying to provide a compromise solution not knowing what the poster's use was for the room.
Even though what I was describing may not be significant in pure RT60 terms, I still don't get how forcing a portion of a wave to travel through more air and through more absorbers before bouncing back at the user from the front can't help. Remember, I was only discussing diffusion on the rear wall, not the sides. If it takes the same amount of time to decay but each wave bounces back at my position fewer times and from more different directions within that space of time, how can that not help the situation?
Besides the above stated, it appears to my ears, to provide 2 other benefits. In surround mode, the rear portion of the surround field gets scattered more evenly thereby increasing the sense of envelopment. In 2 channel, forcing the wave to travel a longer distance before coming back off the front wall makes the space appear acoustically larger than it actually is. Not all rooms require this but you don't run the risk of sucking the life out of the sound if you put some up. Like you said, reflection does not effect the rate of absorbtion.
Also, if I the room is a bit live, the only time I would worry about it is when it is just me in there. At that point, I am probably listening to music so it works better that way. When we are watching movies, there are 4-12 wonderful abosobers that get added to the room called people spread throughout the middle of the space.
I have heard rooms done both ways. Both can sound very good when doing multichannel duty. Like I said before, I have just never been able to find that one sweet spot for stereo when you totally optimize for surround, even when sitting in the nearfield of the front speakers. Just my opinion but I'll sacrifice a tad on the ultimate in multichannel quality to get that sweet spot back.