Originally Posted by cap'n
To summarize one aspect of this disscusion, I think we could agree that in a small room, at the ears of a human subject, the left and right ear signals are correlated to a large degree.
True, but hardly relevant. After all, we're talking about how to create the sensation of a large room inside of a small room. So what we must do is FIX the problem you cite above. The correlation is a problem, and remains so.
Of course, under the right circumstances, our auditory system can detect amazingly small phase differences even at low frequency. The question is whether or to what extent it is audible, and more importantly, if decorrelation is preferred - an assumption which sounds reasonable but that doesnt' make it a true, especially if all factors are taken into consideration. For example if in trying to get some subtle spatial effect you degrade the spatial uniformity, it's not a clear cut improvement. When people have a complaint about bass in a small room, it is almost always "it sounds boomy", or "it sounds thin", or "it sounds boomy here and thin over there", NOT "gee, the subwoofers don't sound spatial enough".
All of which testify exactly to the idea that you haven't broken up the LISTENING ROOM's modes enough. Damping them is great, breaking them up so that they behave (via multiple subs, not by attempting the impossible regarding walls, etc) more like a large venue, on the other hand, at least has a chance of sounding like a large venue. To that end, what you need is a lot of modes, a lot more than a small room will ever provide without some help from electronics. And, what's more, a lot more than you'll ever get with one subwoofer in any location.
Part of what makes large (good) venues smooth is the lack of hot spots, booms here or there, nulls, etc. The way this comes about is not by eliminating nodes, but by creating many, many nodes. Check out Beranek if you don't accept that, it's not my opinion. Measurement, certainly, does bear out the idea remarkably well, though.
This thread reminds me of many discussions I had with David Greisinger, which were fascinating but theoretical. This is why I did the research I did on "stereo bass". You can theorize all you want, but it is just theory until you can back it up with real research. Bill Martens is one of the few who has done such research.
Do you accept the measurements shown in the paper I cited above. Yes or no? If yes, then what's with the 'theoretical' codswallop? If "no" what's your problem with them? They are simple measurements, simply made, and the results are plain as day. Measurements are measurements. As far as I know, that's about as down-to-earth practical as is humanly possible.
So, since when is measurement "theoretical"? By what mechanism do you dare to insinuate my argument here is "theoretical"? It is not, it is based on simple, clear, measurement. Unambiguous measurement, in fact.
I've published 1 paper, which, although it wasn't intended to address this issue, does so in a rather clear and startling manner, as regards the actual content in a large room. It shows, very clearly, that even at low frequencies, in a good large venue (or 3, I would have to go back to see how many, I know it's at least 4, it wasn't particular to any one venue, but I wouldn't call one of them "good" by any reasonable standard) that the soundfield in the bass region is much more highly decorrelated than you expect (or that I expected!), in fact the coherence length (meaning the point at which the correlation drops to 1/e) is remarkably well under 1 wavelength. (And none
of that is even remotely true in a small venue, of course.)
To the perception of phase shifts, you have already stipulated. We have the evidence from large rooms, we have your stipulation. Ergo, we have an effect, unless your stipulation is unwarranted. (and it's not)
So, we have evidence that this is a real
, not theoretical
issue, and that it is audible in large rooms. So we can now abandon "theoretical" insinuations, insults, and name calling, please, and do so completely. So, no more "theoretical" now or ever, in this context. NONE. We are not talking theory, unless by some magic observation has now become theory.
Now, what are you still
All of your arguments about a soundfield in a small room simply do not address any attempt to create
a more complex node structure in the small room, by using multiple sources.
And no, artificial decorrelations are just not a useful thing to do, unless you really do the right
kind of decorrelation. The "hilbert" idea, for instance, decorrelates two signals, but does little, if anything, for the node structure in the small listening room. N.B. Please don't presume that I know how to do the 'right kind' myself, other than by measurement, at this point. I might, I might not, and I don't know the answer to that myself.
Now, as to "smoothness" in the room, allow me to point out that good, large venues are not "smooth" in any sense one would usually use the term. So, creating a "smooth" response in the usual sense is not, can not, sound like a large room.
Now, how do we create that kind of soundfield in a small room? That's the question, not "smoothness" or "decorrelation" of some particular fashion with some particular method.
And this is where the problem with "optimization" comes in. Do you wish to optimize to some particular standard of "smoothness" or do you wish to recreate something like a good, real venue? Do you want to do the same thing when such information is present (which is rare in the present day) as when it's not (for which I think you're doing the right thing)?
Now, suppose I give you a recording with the proper information. What is your system going to do with it?
And therein is my objection to enforcing monophonic bass. You can't use information when you get it, and information that even the uber-denier admits is most likely audible. So, what do you do when you get the information?
(I'm not presently in a position to offer you a germane recording. I doubt I have to explain the problems in being able to release material.)