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Posts: 5109
Location: Brisbane
Joined: September 25, 1999
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My point was basically that a bigger room doesn't automatically reduce the room's contribution and in fact I can think of big spaces which actually increase the room's contribution to the sound. For example I have a recording made inside a large concrete water cistern in Washington State which has a reverberation time of over 40 seconds. You simply can't get away from the room's contribution in a space like that, it simply dominates everything, so size is definitely not an automatic determinant of the level of room contribution. Setup within the room is important too, and depending on the particular room and setup, either one can dominate the other.
My other concern, not stated in my original post but which I will state here, is my frustration with seeing people generalise from one situation while apparently not considering everything relevant to that situation. As I said, larger rooms make it easier to move the speakers and listening position away from the walls, which tends to increase the length of the reflection paths and reduce the level of the reflections relative to the direct sound, thereby reducing the room's effect. It's easy to observe that larger rooms seem to produce results which have less room contribution and to attribute this to nothing other than room size, leading to a generalisation like Mike's, while not considering just what else is changing in the large room setup—ie often distance from walls—and ignoring the effect of that change. Repeat the generalisation too often and people start to think that large rooms are always better and another audio myth is born. Large rooms are often better, but they definitely are not always better. If we understand and acknowledge why large rooms are often better, we may also do something positive about helping people with smaller rooms to get better results by giving them information they can use to help minimise their problems in a smaller room. Moving to a bigger room isn't any solution at all if you don't have a bigger room to move to.
You said:
"The smaller rooms always seem to have a "sharper" sound in the midrange, and I partly credit this to way boundary proximity is affecting wavefront dispersion. But regardless of the facts, in a larger room with a farfield setup I often get the *feeling* that I am hearing less of the room (and more of the music), thanks to the more believable sonic ambience of the relatively cavernous space. "
I'd make 2 comments in response.
First, the frequency at which room response starts to smooth out and modal behaviour stops being significant depends on modal density, the number of modes occurring per octave. The number of modes per octave increases as frequency increases because modes occur at multiples of the fundamental modal frequencies and octaves occur every doubling of frequency. If we have a fundamental mode of 100 Hz, it's next contributions will occur an octave higher at 200 Hz, then at 300 Hz, 400 Hz (the next octave), 500 Hz, 600 Hx, 700 Hz, 800 Hz (the next octave) and so on. The lower the fundamental modal frequencies, the lower also that the modal density required to start smoothing the room's modal response will occur. Big rooms have lower modal fundamental frequencies and smoothing will start to occur at a lower frequency. Modal behaviour can continue to have significant effects up to 300 or 400 Hz, perhaps a little higher in some rooms, and that is well into the midrange. The smaller the room, the higher the modal effects are likely to be noticed so it's possible that the midrange sharpness you refer to may be related to modal behaviour rather than wavefront dispersion, especially if you have noticed the same effect in small rooms with different sorts of speakers which have different wavefront dispersion patterns such as dipoles, bipoles, and line sources as well as the more common box speaker. I'm not saying wavefront dispersion isn't the cause. I'm simply saying that there are room effects which can continue well into the midrange which may also be the issue, or part of the issue, and that different speakers can have very different wavefront dispersion patterns so if you have heard the same thing in rooms with different speaker types, that would make it more likely that something other than wavefront dispersion was the cause.
Second, farfield systems tend to give more of the sort of presentation that one gets mid-hall in a concert hall. For many that sort of presentation is the epitome of the sound of live music. A nearfield setup tends to give a very different presentation and if that presentation is not what a listener is used to, they're likely to think that the nearfield presentation is giving them less of what music really sounds like and, because the farfield setup gives them more of what they believe music sounds like, they could assume that they're hearing less from the room with the farfield setup. Do we say that in the farfield setup you hear a greater contribution from the room because the contribution from the reflected sound is greater in absolute terms or do we say that in the nearfield setup you hear a greater contribution from the room because it minimises the contribution from the reflected sound? Both statements are based on accurate assessments of what is going on in each case.
I suspect that most people will consider room contribution in terms of how much of what they don't want is being contributed so they will say that they hear less contribution from the room which gives the sort of presentation they want, whatever kind of presentation that is. Taking away something which is desired, ie reducing the level of reflected sound below what the listener prefers, will be seen as a room contribution by someone who prefers a farfield setup if this is how they consider what the room contributes to the sound they get and the further the result diverges from what they'd like to achieve, the greater they will regard the contribution from the room. Fewer people will consider room contribution in absolute terms based on the level and character of the reflected sound. Those people will consider that the room's contribution increases as the level of reflected sound rises relative to the level of the direct sound and/or the frequency balance of the reflected sound shifts from that of the direct sound.
I'm definitely in the second of those groups which puts me in what I suspect will be the minority but you may well be in the first. There's nothing wrong with that and it's possible to argue for one way of describing things or the other. It's simply worth noting that you and I may well be saying different things that aren't the contradiction they initially appear to be when you say that the room contribution is less in a farfield setup and I say it is less in a nearfield setup.
I don't want to cast one of those perspectives as "objective" and the other as "subjective" because the tendency is to think of objective as related to something which can be measured and independently verified and subjective as something which can't be measured and independently verified. In this case the room's contribution can most definitely be measured and verified and the issue is not what the results, measured or perceived, are but rather what should be taken as the "standard" when interpreting the results. There is no agreement on what we should be comparing things to when we say the room is making a greater or lesser contribution so the listener making the assessment is forced to supply their own 'standard' to the assessment. I simply think it's worth flagging the point that it often can be less than clear as to just what an apparent disagreement can mean in this sort of discussion.
David Aiken
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