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In Reply to: RE: the glass is half full/the glass is half empty posted by KlausR. on December 19, 2007 at 00:14:56
"Comb filter coloration has been shown to not be a problem. Change in spatial impression in small rooms has never been investigated other than determining absolute thresholds of a single reflection which are higher than the absolute thresholds of detection, at least for artificial signals. No data for music and no data for a single reflection in the presence of multiple reflections. So you simply don't know what appropriate levels are which do not totally remove the reflection."
You're right. I don't have data to tell me precisely what an appropriate level which doesn't totally remove the reflection is, but I do have some data from Toole and Olive that provides a guide by indicating the range between inaudibility of the early reflection and the level at which image degradation starts to occur. Admittedly that data applies to single reflections but the reflection I'm applying it to is also the strongest reflection from that surface and the other reflections are weaker, many significantly weaker and able to be ignored from a practical level because once they're 6 dB below the level of the early reflection they're adding less than 1 dB to the overall level and once they're 9 dB below the early reflection they're adding less than 0.5 dB to the overall level.
So what I do have is some information which provides some good indications of what kind of range the level of the early reflection should be reduced to in order for me to get the benefits I want. That range is quite wide—roughly a 6-8 dB window—and absorption treatments that are practical enough for use in a listening room never achieve total absorption. I don't find achieving a level I regard as appropriate as particularly difficult since what I regard as appropriate is a result that makes me happy. I'm prepared to experiment and fine tune the treatment a little to get a result that I like.
I'm not suggesting that scientific data isn't useful or valuable but I am saying that my goal is not to produce a 'scientifically optimum' result but simply to increase my own listening pleasure. I use acoustic theory to help me change the sound I'm getting in my room to something that I enjoy more, not to dictate what that sound should be. I may not know in advance what level of treatment of the early reflection points will yield the result I'm looking for but I am prepared to be pragmatic about playing around until I get it. My experience has been that it's pretty easy to get an acceptable result and I suspect that's because what is acceptable falls somewhere in a 6-9 dB wide range and that makes it much easier to achieve than it would be if the acceptable window was much narrower.
In fact, my experience and the experience of many others tends to indicate that it's relatively easy to achieve results that are liked by the person doing the treatment and also by others who subsequently listen in the room by simply following a few basic rules about where to place treatments and what sort of treatments to use.
Let's change the subject slightly. I want to ask you a very serious question. You've obviously read extremely widely in acoustics research and you've also obviously thought about it a lot. Since that is the case, why is it that you seem to use that knowledge purely for the purpose of rejecting recommendations for acoustic treatment and arguing that treatment isn't necessary? I agree that it isn't necessary/essential and that I could listen and get enjoyment in an untreated room but I do get more enjoyment and a better appreciation of the music in a treated room. While I haven't read as widely, I've tried to use what knowledge I've gained from my reading to assist in improving the sound I get in my room with what I suspect many would regard as a relatively basic level of acoustic treatment. You on the other hand seem to want to use your knowledge for no other purpose than to argue against acoustic treatment. I simply can't understand why that should be the case. Why spend a considerable amount of time and effort studying acoustics not so that you can use it to improve the listening experience but rather so that you can try to expertly argue that there's no nothing to be gained by acoustic treatment which is the way most of your posts seem to come across to me?
David Aiken
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