Speaker Testing: why mono is better

[Duke]

You are conflating spatial quality (the area where the speaker radiates sound) to things like center imaging and soundstage (stereo spatial quality, if you will), which results from two speakers interactivity while playing a stereo recording.

"Spatial quality" and "sound quality" are the two categories in the monophonic and stereophonic ratings that Amir posted in posts number 132 and 176.

So I think the term is applicable to both mono and stereo, though exactly what "spatial quality" entails is obviously quite different in stereo than in mono.

 

[Blumlein 88]

I'm halfway through your Long post, but must interject our ears already largely ignore early reflections and already largely hear "through" the room as a result.

 

[Blumlein 88]

In response to my post number 295, @hex168 and @Thomas savage expressed interest in my offer to “describe what I believe to be a stereo setup where something desirable happens to the spatial quality which cannot be evaluated by testing a single speaker.” Perhaps @richard12511, @Coach_Kaarlo, and @tuga ought to be notified as well, since they “liked” post number 295.

And I SHOULD HAVE made it clear that I was referring to LISTENING tests, not the actual MEASUREMENTS of a single loudspeaker. My bad, and I hereby excuse any of the five of you who thought I was talking about MEASUREMENTS from having to read the rest of this post. (I suggest you take advantage of that loophole; this is a dreadfully long post.)

Please consider all of this to be my opinion so that I don't have to remember to insert an annoying number of disclaimers.

Here's the TL;DR version: If you take two speakers with narrow and well-controlled patterns and toe them in such that their axes criss-cross in front of the main listening position, their room interaction will result in better spatial qualities than could have been predicted from mono on-axis listening to a single speaker.

And now the long version:

First, let me re-state my opinion regarding mono vs stereo listening tests so that nobody reads through all of this under the assumption that my claim is farther-reaching than it actually is:

I claim that stereo listening is more revealing of spatial quality than single-speaker mono listening is.

And the intention of this post is to present an example of an unorthodox but valid stereo setup whose spatial qualities cannot be adequately evaluated by listening to a single speaker.

For the purpose of this post, let's define “good spatial quality” as, the recording venue's acoustic space perceptually dominating over the playback room's acoustic signature. In other words, a “you are there” illusion is the goal (which of course is also somewhat recording-dependent, so we can only focus on the speakers and their interaction with the listening room).

In the playback room there is in effect a “competition” between the venue cues on the recording (whether said cues be real or engineered) and the "small room signature" cues of the playback room itself. The ear/brain system make its best guess about the acoustic space you are in by drawing from these two groups of acoustic cues. Ideally we'd like to effectively present the venue cues which are on the recording while minimizing undesirable "small room signature" cues, thus enabling a “you are there” illusion. This is of course easier said than done.

At the risk of oversimplifying, the ear looks at three things to judge the size of an acoustic space: The earliest reflections; the reverberation tails; and the temporal "center of gravity" of the reflections. So we have the early reflections, reverberation tails, and temporal "center of gravity" of the venue cues on the recording; and we have the early reflections, reverberation tails, and temporal "center of gravity" native to the playback room. We want to effectively present the first package of cues while disrupting and/or minimizing the second.

Achieving our goal is complicated by the fact that it is the in-room reflections which are the CARRIERS of the venue cues (at least for two-channel). Yes there are venue cues in the direct sound, but that is actually the WORST possible direction for reflections to come from. Reflections coming from many different directions will do a much better job of presenting the venue's spatial cues.

ALL of the in-room reflections are carriers of the desirable venue cues, but the FIRST in-room reflections are also the STRONGEST source of undesirable "small room signature" cues. So the WEAKER the first reflections are (relative to the later ones), the LESS small-room signature we will have superimposed atop the venue cues.

On the other hand the in-room reverberation tails are very effective carriers of the recording venue's reverberation tails, and therefore can play a significant role in creating the illusion of immersion in a much larger acoustic space than the playback room. So we want to preserve these reverberation tails, and of course we want them to be spectrally correct. (If the in-room reverberation tails are spectrally incorrect then the ear/brain system has a harder time identifying them as reflections, which is detrimental for reasons I can explain if anyone is interested.)

So to recap where we are thus far: We want WEAK early reflections because that weakens the playback room's “small room signature”; and we want plenty of spectrally-correct later reflections because they effectively and benignly deliver the recording's venue cues.

There is one more thing that would help: If we can somehow time-delay the first lateral reflections, this would push back in time the temporal "center of gravity" of the in-room reflections. Doing so disrupts the undesirable "small room signature", because a long time-delay for the first lateral reflections tells the ear/brain system that you're in a much bigger room that you actually are. In effect this undermines the plausibility of the “small room signature” package of reflections, making it easier for the ear/brain system to accept the recording's venue cues as the more plausible package of reflections.

(If I didn't put him to sleep, @Kal Rubinson is probably shouting at his computer screen that a good multichannel system already does all of this. And he is right! But let's see how much we can do with just stereo.)

Okay with that long-winded background behind us, let's look at what happens when we use the unorthodox approach to stereo that I briefly described earlier, with narrow-pattern speakers and criss-crossing patterns.

The Gedlee Summa is designed to be used like this. The Summa combines a 15” woofer with a similar-sized round, 90-degree, constant-directivity waveguide. The crossover is around 1 kHz, where the woofer's pattern has narrowed to match that of the waveguide. Here is a polar map of the Summa's frequency response:


View attachment 120715

The designed-for listening axis of the Summa 20 degrees off-axis. You can see this depicted by the red line in the overhead polar response view to the right of the polar map, above. And in the polar map you can see a horizontal black line that is not right smack down the center of the polar map, but is 20 degrees above the center. That is the intended listening axis.

And below is a photo showing how this type of speaker is intended to be set up. The photo is taken from off to one side and you can see that the speaker axes criss-cross in front of the central sweet spot (these speakers aren't Summas):


View attachment 120714


The combination of narrow, well-behaved radiation pattern AND strong toe-results has two major implications for room interaction. First, early same-side-wall reflection is very weak over the imaging-critical upper portion of the spectrum because the speaker's pattern is aimed about 45 degrees AWAY from the same-side wall. Second, the first STRONG lateral reflection is actually the long, across-the-room bounce off the OPPOSITE side wall! Earl Geddes on the subject:

“A reflected signal that arrives at the opposite ear from the direct sound is less perceptible as coloration and image shift than if both signals arrive at the same ear. This is because of head shadowing above about 500 Hz and the fact that our ears can process signals between them. When the two signals arrive at the same ear, the signals are physically merged in space even before they enter the ear and no amount of auditory processing can separate them. When these signals arrive at different ears, the auditory processing system can diminish the adverse effects of these early reflections through cognitive processing between the ears.

“From an acoustics reproduction standpoint then, the loudspeaker system design must help to provide as much delay as possible in the early reflections and allow for speaker placement and orientation such that the earliest reflections occur at opposite ears rather than the same ear. This needs to be done above about 500 Hz. Below 500 Hz other factors, such as room characteristics and our hearing mechanism, may dictate an entirely different approach.

“In order to perform this “trick” for optimizing the early reflections in a small room, two specific source characteristics are required. First, the source directivity must be less than about 90° and second, the listener is not actually on the sources axis! In other words the direct sound, the first arrival sound, is not the axial sound. To achieve a flat response at the listener in this configuration, the loudspeaker must have a flat frequency response off axis. This is virtually never the case with most loudspeakers. Most loudspeakers with a smooth flat axial response will usually not work very well in this configuration.”

So here are the first two advantages of this cross-firing narrow-pattern speaker setup, which would not be revealed by listening to a single speaker on-axis:

1. Reduced coloration and image shift (due to reduced early same-side-wall interaction, and the first strong lateral reflections arriving at the opposite ear); and

2. Reduced “small room signature” (due to weakened early reflections, and pushing the temporal “center of gravity” of the reflections back in time)

Another spatial quality attribute of this setup is that the soundstage holds up much better than normal for off-centerline listeners. The ear/brain system localizes sound by two mechanisms: Arrival time and intensity. With a conventional stereo configuration (speakers toed-in little if any), the soundstage tends to collapse towards the nearest speaker for off-centerline listeners because the nearest speaker “wins” both arrival time and intensity. With narrow-pattern speakers toed-in aggressively (like the approximately 45 degrees you see in the photo above), the near speaker “wins” arrival time but the FAR speaker “win” intensity! This is because, as the photo shows, the off-centerline listener is well off-axis of the near speaker but right smack on-axis (or nearly so) of the far speaker. The two competing localization mechanisms tend towards balancing one another out, and you still get a decent spread of the instruments (including the center vocalist remaining near the center with most recordings) even from locations as far off-centerline as where the photo was taken from. The KEY to this working well is that the response of the near speaker must fall off RAPIDLY and SMOOTHLY as we move off-axis, which is not the case with most loudspeakers.

So we can add one more spatial advantage of narrow-pattern speakers in a cross-firing stereo configuration:

3. Soundstaging holds up much better than normal for off-centerline listeners.

As previously mentioned, the icorrect listening axis of the Summa 20 degrees off-axis. In the following image the black curve across the top is the frequency response at 20 degrees off axis, so (assuming proper set-up) this is the frequency response of the first-arrival sound:


View attachment 120716


The red line is the power response curve, and the white line is the directivity index. Imo both are very good, with the spectral balance of the off-axis energy matching the spectral balance of the first-arrival sound exceptionally well (and imo this is desirable – I can explain my thinking on the subject if anyone is interested).

One consequence of the first-arrival sound being the 20 degrees off-axis sound AND the extreme toe-in is that the perceived tonality is relatively consistent across a wide listening area. And as we move off-axis to either side, the net spectral balance of the first-arrival sound holds up better than is normally the case because the reduction in energy in the top half of the spectrum from the near speaker is being offset by the increase in energy in the top half of the spectrum from the far speaker. This is of course more of a sound quality advantage than a spatial quality advantage, but without it the spatial quality advantage for off-centerline listeners would imo be of academic interest only. So I'm adding it to my list:

4. Reduced spectral discrepancy between the first-arrival and reverberant sound, for off-centerline as well as on-centerline listeners.

And as is hopefully self-evident, advantages 3 and 4 would not be revealed by single-speaker on-axis listening.

So in conclusion I think there is at least one valid stereo configuration with spatial attributes that cannot be evaluated by single-speaker on-axis listening.

The biggest problem is this is all a hypothesis which hasn't been tested. By that I mean comparing it to the other kind of speaker and letting listeners evaluate spatial characteristics without knowing any of the why or how. Crossing by toe in before the listener position with wider directivity speakers might work just as well since the deleterious effect of early reflections from those are mostly ignored by our hearing in the first few milliseconds.

BTW, I don't mean to throw cold water all over these ideas or say they have no merit. Only that we have one reasonably well researched and tested group of results and everything else is conjecture. I'm pretty sure some of it was tested by Toole and his group. What is needed is more testing of the ideas to see if they have legs or no merit.

 

[Francis Vaughan]

There were two references in the video, not one. The second one was the test of different EQ systems with identical speaker and see listener ratings in double blind testing as speaker count changed from mono to 5 channels. That study was from 2008: https://www.aes.org/e-lib/browse.cfm?elib=14622

Indeed. I think my point is more that bringing out the 1983 paper just confuses the issue. It is flawed in that the Quad is sufficiently unlike the other speakers that the resultant (reasonable) criticisms drown out anything much of value.

I'll cherry pick a few bit from the cited 2008 paper that I think are of value to the conversation.

On the subject of why mono should act the way it does in listening:

The exact reason for this effect has never been fully understood, and the most plausible explanations remain speculative and untested [21].

The takeaway being that there is no supporting scientific evidence as to the why. There is experimental evidence of the reality. Claims about stereo confusing the listener and so on have no basis in science. All we know is that mono works better.

On the subject of applicability to speakers with irregular directivity:

This experiment did not test equalizations using a loudspeaker with an irregular directivity above 400 Hz. Any type of loudspeaker-room equalization may not perform as well with these types of loudspeakers, since the equalization may improve the quality of the reflected sounds radiated by the loudspeaker at the expense of compromising its direct sound, and vice versa. We are currently repeating these experiments using such a loudspeaker, and hope to report these results in the near future.

Takeaway - don't use this experiment as evidence that speakers with poor directivity are best evaluated in mono. They might, but this paper does not provide that evidence. (One notes that this also applies to the 1983 paper, this paper does not actually address that paper's results, only citing it for historical provenance.)

On applicability of the conclusions:

The authors hope that consumers do not misapply this experimental finding when selecting their next surround sound system. For example, we do not advocate that consumers throw caution to the wind when selecting loudspeakers for their surround playback systems on the basis that listeners are apparently less fussy and discriminating in surround in comparison to stereo or mono playback. This would be a mistake since a) more experimental validation of the effect is needed and, b) much of the dialogue in multichannel films, television, and radio broadcasts consists of solo voice hard panned to a single speaker – essentially making it a monophonic recording over some duration of the program.

Takeaway - don't start with straw man arguments trying to come up with silly conclusions or refutations.

There is a chain of argument occurring here.
There is very good reason to choose speaker designs that favour good directivity. There is good evidence that speakers with good directivity can be evaluated with high confidence when listened to in mono. There is good evidence that such speakers, with both good directivity and good mono evaluations will work well in multi-channel settings.

There are missing parts to the puzzle.
Speakers with weird directivity errors probably are a bad place to start, but this is not universally true. There exist speakers with carefully crafted directivity (especially dipoles) for which there are good scientific reasons to think also behave well and yield a high quality result. There is thus far no experimental evidence one way or the other as to whether evaluating these in mono is a valid paradigm.

 

[Coach_Kaarlo]

I think the discussion underlines a few problems.

Overall, IMHO, there are so many good reasons to perform mono evaluation as the primary evaluation that it clear it should always be the default.

However, and it pains me somewhat to say it. The original paper Amir and others cite in support of this case is sufficiently weak as to not usefully add to the conversation. It is a very old paper, and using only three speakers, one with a wildly different polar response, which pretty much makes drawing any conclusions in a scientific manner impossible. It provides supporting evidence for the hypothesis, but it is way way short of providing enough evidence on its own. It didn't refute the hypothesis. That is all. Indeed all any experiment can ever do.

What we do do, is accept that the methodology has proven good over the intervening 30 years, and that many people have independently come to the same conclusions. The paper by itself provide nothing but a single data point. There is no additional data as to the reason why the results occur. You can't do that with only a single data point. There are lots of hypotheses as to why the rankings collapse, but the paper provides zero evidence in support of one over another. That research comes later, and sadly, a lot of it seems to have never reached peer reviewed publication.

For solid science one needs lots of careful experiments. And for any given experiment you work with a single hypothesis. This brings us to the reproducibility crisis in science. Social sciences have become so scientifically bankrupt that the realisation has started to sink in that there are entire swathes of research that are simply invalid. Years upon years of published results that have been accepted without question, and turn out to be unreproducible - aka wrong. Science hinges on peer review, and that review means others should reproduce results. The rush to publish impactful work means everyone is trying to be the one with new results, and nobody has been minding the farm. In the social sciences this has lead to terrible research practices, practices that amount to reverse fitting of hypotheses to existing data in a manner that is guaranteed to yield invalid but apparently statistically valid results.

What is needed is more experiments and publication of those experiments. Amir is probably the only person on the planet gearing up to address this. Like all science, it is a work in progress.

Thank you for your post. I cannot agree more.

 

[wpwoodjr]

By whom? A reviewer? If so, in stereo, next to zero. There are incredible number of variables involved in assessment of the spatial quality of a stereo system. How could you possibly rely on any one person's opinion and try to extrapolate to yours and your situation? There are a million ways to position those speakers, adjust their levels, what content is played, where the person sits, etc.

In mono, the assessment can help figure out if you are dealing with a point source or something different.

Really, the best you can hope from a reviewer is correct assessment of the tonality of the speaker. Fortunately that is the dominant factor in speaker preference. What is left is then for you to decide.

It's not hard to hear consistent stereo spatial qualities of a pair of speakers in different situations. What we need is a way to measure stereo spatial quality scientifically.

In mono, what spatial attributes lead to good stereo spatial qualities? What is the research?

> correct assessment of the tonality of the speaker ... is the dominant factor in speaker preference.
What is the research on this for stereo? Is it possible that a speaker with great stereo "you are there" sound staging might be preferred over a less engaging, tonally more accurate speaker? That their over-all quality ratings might favor one in mono and the other in stereo?

 

[Duke]

I'm halfway through your Long post...

I must say that I like your critiques in THIS post far more than in that one you deleted! And I thank you for doing so.

... but must interject our ears already largely ignore early reflections...

Perhaps "largely" but not entirely. Quoting Floyd Toole:

"The contentious issue of side-wall reflections is the present topic. An assertion of some participants in the audio forums is that I am in favor of these lateral reflections in listening rooms. According to some critics, I believe this in apparent ignorance of or dismissal of decades of professional audio “tradition” in which at least the first sidewall reflections are absorbed. Believe me, I am very aware of these points of view, having designed a few recording studios early in my research-scientist career, and also the high-power monitor loudspeakers that went into a couple of them (“Hi Fidelity in the Control Room – Why Not”, db – The Sound Engineering Magazine, Feb. 1979). In those days the main monitor loudspeakers were moderately directional (mid- and high-frequency horns) and sidewalls were usually angled to direct the first lateral reflections into the absorptive/diffusive back wall. It was clear that mixers preferred to be in a strong direct sound field and that is what they got.

"However, as a research scientist, I saw a number of interesting questions to be answered, and so, it turned out, had other investigators. We needed specifics about the audible effects of reflections, and how to quantify them so that we can measure a loudspeaker/room combination and anticipate a subjective impression. We also were interested in whether the requirements for mixing a recording were the same as the requirements for enjoying that recording at home. All of this is discussed in detail over several chapters of my book.

"Chapter 6 shows that in normal rooms the first lateral reflections in rectangular rooms of normal listening and control room dimensions are above the threshold of audibility. They can be heard, but are below the threshold at which the precedence effect breaks down, so there is still a single localized image. They fall into a region where there are varying amounts of "image shift" - the image is either perceived to move slightly or to be stretched slightly in the direction of the reflection. I, and others, spent hours in anechoic chamber simulations of direct and reflected sounds and can confidently state that the effects, while audible in direct A vs. B comparisons, are rather subtle. Was it ever unpleasant? No, the apparent size and/or location of the sound image was just slightly changed. The effect was smaller than tilting the head a small distance left or right of precise stereo center. The dramatic change happened when the precedence effect broke down and two images were perceived – that was a problem. The strength and spectrum of any reflection depends on the strength and spectrum of the sound radiated in that specific direction by the loudspeaker, and by the frequency-dependent acoustical performance of the reflecting surface." [Emphasis mine]

... and already largely hear "through" the room as a result.

I don't dispute the ear's ability to largely "hear through" the room when it comes to ranking loudspeaker preference, which is the context within which Toole wrote those words.

The biggest problem is this is all a hypothesis which hasn't been tested.

If the "biggest problem" with my long post is that it is "all a hypothesis", I can live with that. It has been tested but not, to the best of my knowledge, under conditions which would have any credibility on this forum. And on a site which has "Science" as its middle name, I would hope that "hypothesis" is not necessarily a pejorative term.

Crossing by toe in before the listener position with wider directivity speakers might work just as well...

It might.

The intention of my long post was to "present an example of an unorthodox but valid stereo setup whose spatial qualities cannot be adequately evaluated by listening to a single speaker."

So if there are more such examples than the one I described, SWEET!!

 

[Blumlein 88]

And I must say that I like your critiques in THIS post far more than in that one you deleted! And I thank you for doing so.




Quoting Floyd Toole:

"The contentious issue of side-wall reflections is the present topic. An assertion of some participants in the audio forums is that I am in favor of these lateral reflections in listening rooms. According to some critics, I believe this in apparent ignorance of or dismissal of decades of professional audio “tradition” in which at least the first sidewall reflections are absorbed. Believe me, I am very aware of these points of view, having designed a few recording studios early in my research-scientist career, and also the high-power monitor loudspeakers that went into a couple of them (“Hi Fidelity in the Control Room – Why Not”, db – The Sound Engineering Magazine, Feb. 1979). In those days the main monitor loudspeakers were moderately directional (mid- and high-frequency horns) and sidewalls were usually angled to direct the first lateral reflections into the absorptive/diffusive back wall. It was clear that mixers preferred to be in a strong direct sound field and that is what they got.

"However, as a research scientist, I saw a number of interesting questions to be answered, and so, it turned out, had other investigators. We needed specifics about the audible effects of reflections, and how to quantify them so that we can measure a loudspeaker/room combination and anticipate a subjective impression. We also were interested in whether the requirements for mixing a recording were the same as the requirements for enjoying that recording at home. All of this is discussed in detail over several chapters of my book.

"Chapter 6 shows that in normal rooms the first lateral reflections in rectangular rooms of normal listening and control room dimensions are above the threshold of audibility. They can be heard, but are below the threshold at which the precedence effect breaks down, so there is still a single localized image. They fall into a region where there are varying amounts of "image shift" - the image is either perceived to move slightly or to be stretched slightly in the direction of the reflection. I, and others, spent hours in anechoic chamber simulations of direct and reflected sounds and can confidently state that the effects, while audible in direct A vs. B comparisons, are rather subtle. Was it ever unpleasant? No, the apparent size and/or location of the sound image was just slightly changed. The effect was smaller than tilting the head a small distance left or right of precise stereo center. The dramatic change happened when the precedence effect broke down and two images were perceived – that was a problem. The strength and spectrum of any reflection depends on the strength and spectrum of the sound radiated in that specific direction by the loudspeaker, and by the frequency-dependent acoustical performance of the reflecting surface." [Emphasis mine]




I don't dispute the ear's ability to largely "hear through" the room when it comes to ranking loudspeaker preference, which is the context within which Toole wrote those words.




If the "biggest problem" with my long post is that it is "all a hypothesis", I can live with that. It has been tested but not, to the best of my knowledge, under conditions which would have any credibility on this forum. And on a site which has "Science" as its middle name, I would hope that "hypothesis" is not necessarily a pejorative term.




It might.

The intention of my long post was to "present an example of an unorthodox but valid stereo setup whose spatial qualities cannot be adequately evaluated by listening to a single speaker."

So if there are more such examples than the one I described, SWEET!!

I'm okay with all of that and certainly hypothesis is not a dirty word.

This part you close with however is still out there waiting to be confirmed or not:
The intention of my long post was to "present an example of an unorthodox but valid stereo setup whose spatial qualities cannot be adequately evaluated by listening to a single speaker."

For what it is worth I've typically crossed my panel ESL's in front of the LP. That was my preference.

 

[richard12511]

The biggest problem is this is all a hypothesis which hasn't been tested. By that I mean comparing it to the other kind of speaker and letting listeners evaluate spatial characteristics without knowing any of the why or how. Crossing by toe in before the listener position with wider directivity speakers might work just as well since the deleterious effect of early reflections from those are mostly ignored by our hearing in the first few milliseconds.

BTW, I don't mean to throw cold water all over these ideas or say they have no merit. Only that we have one reasonably well researched and tested group of results and everything else is conjecture. I'm pretty sure some of it was tested by Toole and his group. What is needed is more testing of the ideas to see if they have legs or no merit.

I tried extreme toe in with my 8351bs, but it didn't work at all. It works remarkably well with my JTR speakers, though.

I remember when I first discovered extreme toe in with the JTRs. It changed the way I viewed those speakers, completely. By far their biggest weakness before that was the tiny sweet spot. Extreme toe in took that weakness, and made it a strength.

Extreme toe in is definitely a thing that only works in stereo, and really only works with very narrow dispersion speakers. Whether it's enough to change the preference from mono to stereo... that I'm not sure. It solves the head in vice sweet spot issue for narrow dispersion speakers, but it doesn't solve the lack of envelopment problem. Wide dispersion still has that advantage.

 

[amirm]

Takeaway - don't use this experiment as evidence that speakers with poor directivity are best evaluated in mono.

That comment relates to equalization aspect of the research paper, not mono vs stereo:

That is the core thesis of the paper. The mono vs stereo/multichannel is a sidebar.

 

[amirm]

Takeaway - don't start with straw man arguments trying to come up with silly conclusions or refutations.

Not really. The second part of what you quoted regarding center speaker being mono proves the point, than add caution to it.

 

[amirm]

Here's the TL;DR version: If you take two speakers with narrow and well-controlled patterns and toe them in such that their axes criss-cross in front of the main listening position, their room interaction will result in better spatial qualities than could have been predicted from mono on-axis listening to a single speaker.

Seems to me that is a technique for speaker selection that is independent of which speaker is better. I could come up with a scheme where one speaker is behind you and one is in the front and say that this requires than mono as well. What would be the point of that?

Whether one can or cannot create a time intensity trading scheme can be concluded using directivity information. It may not need any listening tests anyway other than confirming that such a scheme works.

 

[wpwoodjr]

> correct assessment of the tonality of the speaker ... is the dominant factor in speaker preference.
Found something that backs this up: https://asa.scitation.org/doi/10.1121/1.1945368

ABSTRACT
Mean opinion score ratings of reproduced sound quality typically pool all contributing perceptual factors into a single rating of basic audio quality. In order to improve understanding of the trade-offs between selected sound quality degradations that might arise in systems for the delivery of high quality multichannel audio, it was necessary to evaluate the influence of timbral and spatial fidelity changes on basic audio quality grades. The relationship between listener ratings of degraded multichannel audio quality on one timbral and two spatial fidelity scales was exploited to predict basic audio quality ratings of the same material using a regression model. It was found that timbral fidelity ratings dominated but that spatial fidelity predicted a substantial proportion of the basic audio quality.

So given that spatial fidelity is important too, it would be great if that could be measured objectively.

 

[Duke]

[Floyd Toole] said that the largest source of ambience will dominate the spatial presentation... if a room is more reverberant than the recording, the room's character will lead the listener impression. But if the recording featured stronger reverberance than the room, the recording will lead the listener impression. At least in this equation the speaker has only a contributing, not a dominant role.

Excellent point!

Post number 339 can be read as a suggestion for one approach by which speakers can help tip the balance in favor of the recording's ambience.

In a particular blind test the Revel Salon 2 performed better than the JBL 2 (once again showing speakers with wide dispersion may be subjectively preferable than better measuring speakers with narrower directivity).

My understanding is that it was a controlled blind mono listening test, single speaker vs single speaker, with the speaker positioned well away from the side walls. If I recall correctly, Floyd Toole didn't consider the Revel's margin of victory to be very significant.

In mono listening tests (e.g., at Harman), I listen differently than I do when listening to music and I never listen to music in mono. So, I pay attention to perceived FR and tonal balance, detail/transparency and dynamics. Nothing spatial. OTOH, when listening to music in stereo or multichannel, soundstage is very important, perhaps primary, to me.

Klippel (yes, that Klippel) found that the “feeling of space” makes a 50% contribution to "naturalness” (realism and accuracy), and a 70%(!) contribution to "pleasantness" (general satisfaction or preference). [blasphemy]If we take this at face value, the implication is that the "feeling of space" (soundstage, ambience, imaging, immersion, envelopment) matters as much or more than all those other factors which are MUCH easier to measure.[/blasphemy]

That said, my brain keeps coming back to Toole's statement that they've been doing this for 30 years, and there have been 0 exceptions of mono to stereo preference changing. While I don't think that single study is sufficient, I would have to agree that 30 years worth of similar data probably is. If it really were possible for preference to change from mono to stereo, it almost surely would have happened by now, and Toole's opinion would have changed accordingly. The fact that Toole's opinion hasn't changed after repeat testing really lends credit to his current opinion(imo. @Blumlein 88 pointed this out in a previous post, and I completely agree. Harman has access to much more mono vs stereo data than we do, so I think we should be careful about extracting conclusions based on that one study.

Unfortunately I TOTALLY AGREE with everything you say here, which means that despite the long-winded defense of my contrarian hypothesis, I'm FAR from certain about it (which I probably shouldn't admit, so don't tell anyone). I just hope that @Floyd Toole doesn't show up and put me in my place...

I'm okay with all of that and certainly hypothesis is not a dirty word.

Thank you!

This part you close with however is still out there waiting to be confirmed or not:
The intention of my long post was to "present an example of an unorthodox but valid stereo setup whose spatial qualities cannot be adequately evaluated by listening to a single speaker."

Agreed.

For what it is worth I've typically crossed my panel ESL's in front of the LP. That was my preference.

Despite your sample size being way too small to have any credibility around here, not to mention the glaring flaws with your test methodology, I believe you! (Sorry... couldn't resist having a little fun there.)

Seems to me that is a technique for speaker selection that is independent of which speaker is better.

Maybe I'm really dense, but it's not clear to me how you reached this conclusion. Could you elaborate?

I could come up with a scheme where one speaker is behind you and one is in the front and say that this requires than mono as well. What would be the point of that.

I have no idea.

What I claim is that the stereo setup I described would exhibit spatial attributes which cannot be evaluated in a mono listening test. Those attributes include:

1. Reduced image shift (and reduced coloration) due to reduced early same-side-wall interaction, and due to the first strong lateral reflections arriving at the opposite ear;

2. Reduced “small room signature” due to weakened early reflections, decorrelation, and pushing the temporal “center of gravity” of the reflections back in time;

3. Soundstaging holds up much better than normal for off-centerline listeners; and

4. Reduced spectral discrepancy between the first-arrival and reverberant sound, for off-centerline as well as on-centerline listeners (this is not, strictly speaking, a spatial attribute, but it helps make #3 useful in practice).

It is possible that I am mistaken. If so, then how would preference scores in mono listening be predictive of the presence (or absence) of any of these four attributes, and/or their contribution (or lack thereof) to spatial quality in stereo?

Whether one can or cannot create a time intensity trading scheme can be concluded using directivity information. It may not need any listening tests anyway other than confirming that such a scheme works.

I AGREE that the effectiveness of time/intensity trading can be evaluated by looking at the directivity information of a single loudspeaker!

Can the spatial performance of a time/intensity trading configuration be evaluated by controlled blind listening to a single loudspeaker? If so, how?

It seems intuitive to me that mono listening thoroughly evaluates the effect on Apparent Source Width (ASW) of the sidewall reflections. Are there other aspects of spatial quality in stereo which ARE effectively evaluated by single-speaker mono listening?

And, am I mistaken in my assumption that there is a lot more to spatial quality in stereo than ASW?

I tried extreme toe in with my 8351bs, but it didn't work at all. It works remarkably well with my JTR speakers, though.

I remember when I first discovered extreme toe in with the JTRs. It changed the way I viewed those speakers, completely. By far their biggest weakness before that was the tiny sweet spot. Extreme toe in took that weakness, and made it a strength.

This makes total sense to me (surprise, surprise).

Extreme toe in... doesn't solve the lack of envelopment problem. Wide dispersion still has that advantage.

Earl Geddes advocates having a relatively "live" listening space for narrow-dispersion speakers, so that there is plenty of spectrally-correct late-arrival reflections. Not that this all by itself can make up for the envelopment advantage a good wide dispersion speaker typically enjoys, but it can help.

 

[amirm]

I AGREE that the effectiveness of time/intensity trading can be evaluated by looking at the directivity information of a single loudspeaker!

Can the spatial performance of a time/intensity trading configuration be evaluated by controlled blind listening to a single loudspeaker? If so, how?

If the first sentence does the job objectively, what use is a subjective test of the same?

 

[Duke]

If the first sentence does the job objectively, what use is a subjective test of the same?

I think I see your point: Directivity data is sufficient to objectively evaluate time-intensity trading. Got it, no problem.

I've been looking at a different topic (time/intensity trading was my example, not my topic). Let me phrase it as a question:

In YOUR opinion, does spatial quality in mono listening accurately predict spatial quality in stereo listening?

 

[Blumlein 88]

I think I see your point: Directivity data is sufficient to objectively evaluate time-intensity trading. Got it, no problem.

I've been looking at a different topic (time/intensity trading was my example, not my topic). Let me phrase it as a question:

In YOUR opinion, does spatial quality in mono accurately predict spatial quality in stereo?

Just a quick take on it. If your speakers are rather narrow in directivity the spatiality desired in stereo may be rather picky to achieve. If your speakers are rather wide in their dispersion, you might not achieve optimum spatial vs imaging properties that are recorded on the source and will have little adjustment to fix that. So once again, moderate controlled directivity would seem to offer a fairly certain chance for good stereo effect that isn't overly critical about positioning and yet is controlled enough excessive room reflections don't interfere with the desired imaging and spatial balance. Which would point back to mono testing with moderate controlled directivity in speakers being a most often preferred situation.

One could imagine all sorts of extreme designs that don't fit neatly into those broad categories, but the wise path is to take what has become known and avoid those.

Stupid car analogy.
A Camry may be a most rational fit for most personal transportation needs. But some will still want a McLaren or a Range Rover. The latter aren't about the science of personal transportation or how best to transport in most circumstances. It is about more than that. As long as you don't lie to yourself about that then those other options are okay. You don't need to attack the fitness of a Camry for the basic family car in order to have those other 4 wheeled devices.

 

[Duke]

If your speakers are rather narrow in directivity the spatiality desired in stereo may be rather picky to achieve.

Agreed.

If your speakers are rather wide in their dispersion, you might not achieve optimum spatial vs imaging properties that are recorded on the source and will have little adjustment to fix that.

Agreed.

So once again, moderate controlled directivity would seem to offer a fairly certain chance for good stereo effect that isn't overly critical about positioning and yet is controlled enough excessive room reflections don't interfere with the desired imaging and spatial balance. Which would point back to mono testing with moderate controlled directivity in speakers being a most often preferred situation.

All of this sounds very reasonable.

One could imagine all sorts of extreme designs that don't fit neatly into those broad categories, but the wise path is to take what has become known and avoid those.

Yes. The wise man understands and accepts the way things are, and makes the best of it.

The fool refuses to accept the way things are and stubbornly insists he can make things better.

Therefore all progress is made by fools.

(Okay, I know that was an exaggeration. Seriously, I think those attributes which confer precise imaging and those which confer envelopment and immersion are not necessarily mutually exclusive, nor impractical to implement simultaneously.)

 

[Duke]

There are lots of hypotheses as to why the rankings collapse, but the paper provides zero evidence in support of one over another. That research comes later, and sadly, a lot of it seems to have never reached peer reviewed publication.

Do you have any thoughts you'd feel comfortable sharing about why the rankings collapse in stereo?

 

[tuga]

There were two references in the video, not one. The second one was the test of different EQ systems with identical speaker and see listener ratings in double blind testing as speaker count changed from mono to 5 channels. That study was from 2008: https://www.aes.org/e-lib/browse.cfm?elib=14622

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Since the only variable here was frequency response, it shows clearly that we are better off doing mono testing to determine the most important factor in listener performance.

No one is questioning the effectiveness of single-speaker testing as a means to assess spectral defects.
What I and apparently others are suggesting is that stereo listening should be used as a complement to single-speaker listening for assessing spatial quality performance because it is fitter for that purpose.

The same is true for my criticism of the Spinorama: all that I am saying is that it is insuficient to fully characterise speaker measured performance. HD and IMD measurements, individual driver measurements, decay, step response, cabinet resonances all provide important complementary information.