I don't think their tests are showing this. They have recently gotten excited about room curves and the earlier reflections but I haven't seen a good reason for this other than their ability to predict the room curve has developed.
All the classic Toole tests showed that system power response was well below axial response in importance. Floyd concluded his early two part paper by saying that directivity index or system power response was a poor determinant other than, when strong peaks were present, it was a useful indicator of audible resonances. Certainly the preference ranking of his early paper showed that systems could be well ranked by looking at axial or "listening window" results alone (as he commented). Power response was not well correlated with the rank ordering and was also why Toole and Olive come down hard on the older consumer Reports tests.
Lipshitz and Vanderkooy also found poor correlation between power response or d.i. and sound quality. They concluded, as has nearly everyone else, that improving power response at the expense of axial response was a step in the wrong direction. That flat power response even with flat axial response, tended to sound too bright. That holes in the power response were generally inaudible (but not peaks).
Another friend of mine worked on the Mirage Omnisats. He found that, due to their very wide dispersion, that they needed to be given a downhill response trend to sound balanced. Flatter power response had to be compensated for.
Toole does find that speakers can be too directional. His highest ranked speakers tend to be conventional systems with conventional directivity. In other words, baffled speakers with direct radiators and gradually climbing d.i.s up to a max of 10dB or less at highest frequencies, less below (typically a midrange d.i. of 6). One of the dipoles that he included in his tests was the Quad ESL 63 and it is ranked downwards by the listeners for a lack of spaciousness.
The Bech study I just quoted found that the reflection level in the upper mids seemed to be important, and when reflections had a deficiency in the 1 to 3k region it just meant the overall reflection could be raised for the same effect. The particular response curve for a reflection was otherwise of little importance.
It is tempting when you market speakers with smooth directivity to proclaim that flatter room reflections must lead to a better listening experience. It is a simple and appealing arguement, but I would suggest that it is marketing rather than science.
Regards,
David
Dave
There is hardly complete agreement on this issue.
Greisinger claims that Toole's results do not apply to complex signals and he finds that the early reflections are indeed detrimental to sound quality. I agree with Greisinger and have never accepted Toole's claims in this regard, But perhaps Olive and all are changing on this position, as you say, and maybe for "good reason".
Optimizing sound power without due regard to listening axis response (please note that axial and listening axis are NOT necessarily the same thing) is clearly wrong. Flat power response with flat listening axis response is indeed "bright" since this situation is unnatural. I do not recommend a perfectly flat power response, but a slowly falling one.
But your implication that constant directivity is not a good thing does not really have much support. Not even by Olive. Olive found that room EQ that was preferred tended to correct for a bad power response (i.e. not CD). This means that while power response may not be as important as listening axis response it is not unimportant either.
So no, I don't agree with your conclusions, although they may be convenient for you.
There is hardly complete agreement on this issue.
Greisinger claims that Toole's results do not apply to complex signals and he finds that the early reflections are indeed detrimental to sound quality. I agree with Greisinger and have never accepted Toole's claims in this regard, But perhaps Olive and all are changing on this position, as you say, and maybe for "good reason".
Optimizing sound power without due regard to listening axis response (please note that axial and listening axis are NOT necessarily the same thing) is clearly wrong. Flat power response with flat listening axis response is indeed "bright" since this situation is unnatural. I do not recommend a perfectly flat power response, but a slowly falling one.
But your implication that constant directivity is not a good thing does not really have much support. Not even by Olive. Olive found that room EQ that was preferred tended to correct for a bad power response (i.e. not CD). This means that while power response may not be as important as listening axis response it is not unimportant either.
So no, I don't agree with your conclusions, although they may be convenient for you.
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Toole's results are all achieved with listening tests on conventional music, so I'm not sure why a distinction about complex signals should be made. I'm also not talking about early reflection because I don't believe that Toole is a proponent of them. He clearly like a greater number of later reflections than those who would argue for higher directivity. It isn't clear to me that Toole and Griesinger are at odds.
We can both agree on a slowly falling power response as being a good target. The remaining issue is whether the shape of the the power response curve is of high importance and whether there is a preferred general amount of directivity. I maintain that, for those who have done the studies, the shape of power response is a very secondary effect. Toole and Lipshitz and Vanderkooy show that power response can have significant holes in it and no particular shape is required. It is secondary to axial response (listening axis if you will). As I mention, a system with intentionally low directivity (in the omni class) will require some compensating adjustment to the axial response. Conversly, for those that aim for higher directivity it would make sense that power response shape becomes even less important.
I am aware the Olive has jumped on the room correction bandwagon and I have discussed with him the problems of steady state room correction, not the least of which is the need for arbitrary non flat targets that appear to change with every room. If power response "may not be as important as listening axis response" then we do indeed fall into a trap when we start to adjust the one at the expense of the other.
It would be more convenient for me to proclaim the high importance of CD, as I was a little earlier to that party. I am still in favor of systems with the best possible polar response, at least throughout any likely listening window. I am just leary of those that start to proclaim that power response or system directivity are more important than they truly are. Again, it is an appealing arguement to say that every reflection should mimic the direct sound, that the power response must have a particular shape or be free from any holes or that even the phase response of reflection should match the first arrival.
There just isn't any proof that these claims are valid.
David S.
I think it would help the arguments if conditions were stated. If one were seated in the sweet spot, would power response matter?
On the other hand, if one wanted a horizontally extended sweet spot, as in wider seating positions while viewing a home theater, off axis response, i.e. power response, would seem to be very beneficial. And, if beneficial to the widest positioned seats, would flat power response possibly not be the best it could be at the central seat? In other words, is there a trade off to better fidelity at the central seat for making the outside seats better?
On the other hand, if one wanted a horizontally extended sweet spot, as in wider seating positions while viewing a home theater, off axis response, i.e. power response, would seem to be very beneficial. And, if beneficial to the widest positioned seats, would flat power response possibly not be the best it could be at the central seat? In other words, is there a trade off to better fidelity at the central seat for making the outside seats better?
Dave
I think that we are converging on agreement.
Listening axis response, i.e. the direct response is paramount, no argument there. Second, to me at least, is the absence of very early reflections and diffractions for good imaging. I use Greisingers work here as well as Blauert as support. (Toole will disagree.) This highlights the need for higher than average directivity in smaller rooms with nearby boundaries. Third, is the need for a room response, steady state response, reverberant field, whatever you want to call it to be of the same tonal character as the direct field or this reverberant energy will color the sound. This means a smooth power response and DI. Holes in the power response will not be as severe an issue as peaks can be.
The frontal polar response should be uniform if toe-in is used otherwise toe-in does not work. Without toe-in you will almost always have the "head-in-a-vice" problem.
These are my claims and I do not see how they differ all that much from what you are saying.
Greisinger does make a point of specifically disagreeing with Toole in one of his papers and it is in regards to the perception of reflections, etc. I don't recall the exact paper of Toole's, but Greisinger did refute it in very strong terms. I know that much of Toole's work used signals not music. I don't know which ones he did with music.
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Good point, Pooge.
If you're close to the speakers, you'll primarily hear the direct sound. Sit at the other end of a large room, and in relative terms sound power will have a much more significant effect on the sound. A speaker with a clear downward tilt in the power response may sound fine when listened to in the near-field, but too dull when listened to from farther away.
Also, it is my experience that the direct to reflected ratio has a profound effect on the clarity and immediacy of the sound. The direct to reflected ratio is a function of the physical locations of the speakers and listeners within the room, the amount of damping in the room and the directivity of the speakers.
In my opinion it is therefore a logical conclusion that there is not one ideal directivity factor/index. It depends on the specific conditions and to some extent (acquired) taste. In most practical situations I would argue for a slightly higher directivity than you'll see with conventional speakers, but in my own specific situation I prefer my current very-wide dispersion speakers.
Horses for courses.
If you're close to the speakers, you'll primarily hear the direct sound. Sit at the other end of a large room, and in relative terms sound power will have a much more significant effect on the sound. A speaker with a clear downward tilt in the power response may sound fine when listened to in the near-field, but too dull when listened to from farther away.
Also, it is my experience that the direct to reflected ratio has a profound effect on the clarity and immediacy of the sound. The direct to reflected ratio is a function of the physical locations of the speakers and listeners within the room, the amount of damping in the room and the directivity of the speakers.
In my opinion it is therefore a logical conclusion that there is not one ideal directivity factor/index. It depends on the specific conditions and to some extent (acquired) taste. In most practical situations I would argue for a slightly higher directivity than you'll see with conventional speakers, but in my own specific situation I prefer my current very-wide dispersion speakers.
Horses for courses.
Was it in this paper?
Power Response of Loudspeakers with Noncoincident Drivers-The Influence of Crossover Design
I think it was the case in monophonic tests, but it went up significantly in stereo tests.
Maybe 5.1 or 3 channels would again give different results and favor higher directivity speakers?
Reminds me of a certain paper on a certain JBL studio monitor
I know they are not completely the same, but for ease of discussion, please don't send this off into an unnecessary tangent.
Good question. IMO there isn't as long as the speaker has a smooth response at all off axis positions at which one might sit. This, to me, is one of the more important aspects for Constant Directivity. Smooth power response is another, which is more important really isn't an issue because with either you tend to get both.
I guess a better way of stating my question is the reverse. Is there a detriment to an audiophile introvert who primarily sits in the ideal center position, if the speakers are not CD or have a smooth power response?
If off-axis FR is constant and flat, more hf energy will go into the room. However, if hf energy is attenuated to a greater degree, does this matter that much to the centrally seated listener?
No, this one:
AES E-Library Experiments in Direct/Reverberant Ratio Modification
Yes, it was marked down severly in the mono tests and came back up to some degree in the stereo tests. I agree that having more channels makes for a stronger case for directional speakers.
2 channel is full of compromises. Higher directivity might give sharper definition, but wider directivity will lead to a more realistic spatial impression, even in a small room. In the case of very dead speakers there is lttle or no sound outside of the span of the speakers. This is totally unlike the sound of any natural venue.
Reminds me of a certain paper on a certain JBL studio monitor
Indeed, and I had a strong debate with upper management when they started to claim that improved power response was the primary benefit. It wasn't.
Regards,
David
They're not the same at all, and mixing them together just confuses the situation. I'm not trying to derail the conversation, but point this out so other readers don't get the wrong idea.
Your implication was that to get a good "off axis" response that you need a flat power response. This is not true.
Power response on its own tells you nothing about what the response will be on any particular axis, you could have a flat power response but a very non flat response on any given axis for instance.
In your previous post where you're talking about getting a good "off axis" response for listeners to the sides on a home theatre system its not flat power response you want, but a uniform response within a defined listening window.
A uniform flat response within a certain horizontal and vertical angle off axis window is exactly what a CD system can achieve. It won't have a flat power response though, and nor should it.
Sorry, either you have this wrong or I don't understand.
If we ignore what happens outside of the "axis window" as you describe, a CD system must have a flat power response. Unless the response outside of the window is a complete mess, or it is much lower in level, it won't change this fact substantially.
Curious, they state in the abstract that the sound quality is a function of both the direct and reverberant fields. I understood you to be using this paper as support for the position that the reverberant response doesn't matter.
I should also point out that I recommend much more reverberant spaces than "normal" - an assumption made in this paper. I claim that narrow directivity allows this (naturally low very early reflections) which then yields good imaging AND good spaciousness. A combination that cannot be achieved any other way. So many of these papers make assumptions that limit their applicability. (PS. A more reverberant room would likely have more dependence on the power response than a dead one.)
Would depend on the room. In a very dead room not so much, but then it will sound like headphones with no room spaciousness. To get back spaciousness you would need a more reverberant room but then the off-axis aberrations will get to you. And if there is a lot of off axis energy then the very early reflections will also degrade the image. No ideal options, but for some this may be acceptable.
Exactly the focus I am after. While you advocate a certain flavor of CD, and I am by no means criticizing it where your preference for a very wide sweet spot is warranted and/or an ideal room is contructed, it always boils down to a system approach. The question is, what system approach can be accomplished, and what tradeoffs are necessary for variously obtainable conditions?
That being said, if the average room cannot be made ideal for any reason, whether it be cost, asthetics, or whatever, how can one place a value judgement on the necessity or importance of CD?
I appreciate your view recognizing the rising establishment of the home theater market, and have no argument with your advocating your criteria for that market, including that of an "ideal" room. What I don't have the feel for is what importance CD has in MY room, which may or may not approach your ideal room.
Studies like Toole's seem to rely on user <i>preferences</i>. But do these users have the SAME preferences as me?? You state that preferences don't matter, it is whether or not it measures properly. Yet, you state that a falling response with frequency is preferable. This would seem to contradict the measurement is everything principle. To be fair, (and I am only playing devil's advocate here to flesh out a discussion that hopefully doesn't degrade into yet another objectivist vs. subjectivist debate), you do research to determine what is actually audible and then use that as a basis for measurement, and your measurements have some basis in "preferences" from your studies of audibility. (OK, equating preferences with audibility may be a stretch. Nevertheless, subjective responses are required.) However, whether or not a piece of equipment is "good" or not seems like a bit of subjectivism is required in the process.
For example, studies often state that FR is the highest in importance as a preference in evaluating quality. Well, I question that. Preference to what? Accuracy? Emotions? Something else? How can one possibly know if a recording is accurate?? How does one know if the recording preserves any hint of accuracy by being close miked? A seating position in a concert hall may have a totally different timbre than at another seat, yet the timbre at each position, while different, is accurate for that position. Where you are seated with respect to one instrument, like a horn, will make a bigger difference than say, a kettle drum. Yet, even with differences in tone, both are accurate in the live event.
To my experience, clean dynamics is that facet of reproduction that makes reproduction more <u>believable</u> with respect to anything having lesser dynamics unless there is some other major flaw. To be sure, some horns have majors flaws. But done well, the dynamics of high efficiency sound more believable to me than any other form of reproduction that doesn't get this right.
I understand the desired preference for timbral "accuracy". But unless the overall reproduction is BELIEVABLE, I don't equate FR in as high a regard of importance as made out in the press or various studies. But that's just my preference...
Pooge
I don't disagree with you for the most part.
I prefer measurements in all cases, but there are a few exceptions - you found one.
If "preference" is your "thing" then all bets are off on ever coming to a consensus on anything. Only you can answer the questions for you. That makes any discussion like this pointless and why have it? Only when one has calibrated perception with measurements can one talk about something objectively in a manner that is independent of "preference". That's my approach. Doesn't sound like its yours. No argument there. But then there isn't any point in going on with "Well I like this.", "No, I like this.", "Bob likes that and he says he is an audiophile". I just find those kinds of discussions pointless.
I don't have an average room, I am not an average listener, and I am after the absolute in "accuracy" as judged by measurements that have been shown to correlate with perception. At least that approach is one that actually does have an answer.
When you can quantify all of the various subjective aspects that you mention then we can have an interesting discussion. Otherwise it's just "He said, she said."
I don't disagree with you for the most part.
I prefer measurements in all cases, but there are a few exceptions - you found one.
If "preference" is your "thing" then all bets are off on ever coming to a consensus on anything. Only you can answer the questions for you. That makes any discussion like this pointless and why have it? Only when one has calibrated perception with measurements can one talk about something objectively in a manner that is independent of "preference". That's my approach. Doesn't sound like its yours. No argument there. But then there isn't any point in going on with "Well I like this.", "No, I like this.", "Bob likes that and he says he is an audiophile". I just find those kinds of discussions pointless.
I don't have an average room, I am not an average listener, and I am after the absolute in "accuracy" as judged by measurements that have been shown to correlate with perception. At least that approach is one that actually does have an answer.
When you can quantify all of the various subjective aspects that you mention then we can have an interesting discussion. Otherwise it's just "He said, she said."
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