Floyd Toole: Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms (AES Presents) 3rd Edition - Discussion Thread

[BenToronto]

When it comes to double-blind instant A-B testing, can't beat Toole's Can. Nat. Res. Council methods. Not quite saying he is measuring the right things the right way, but definitely without tell-tale clues.

Yes, challenges to validity but clean work.

 

[Sal1950]

Heh, entirely likely effect in that scenario, of course.. Now, you two, come up with an experimental test method to eliminate or minimize the test subject's "closer attention effect" with two, serially listened to pieces of equipment. Assume there might be an actual effect, besides the possible psycoacoustic effect.

More of a challenge than it at first seems, when you think about it, yes?

It's not easy, this testing stuff...

With devising the complete procedures the idea will always be the same, close your eyes. LOL
In this particular case someone would be switching the new and old components without the listener knowing what has been done.
Can the listener repeatedly identify one from the other or if nothing was changed at all.
Quite difficult and a lot of work, volume levels have to be matched between the two within 0.25 db, more depending on whats being switched.
It's very easy to hypothesize over cause and effect, a whole another keddle of fish to run scientifically valid tests.

 

[mechtheist]

Does Uncle Jack sound different in you kitchen versus on the sidewalk?

Toole is a PhD physicist who has tried to walk the line between acoustics and perception. As a human factors psychologist, I feel better when people with my kind of training do acoustics than when people with his kind of training try to do psychology. Maybe just me.

Do you do psychoacoustics? It's painful to not give that term an alternative usage for confronting the speaker wires on blocks types.

A couple of great examples of how profoundly our brains construct our perceptions is how we can hear the same tonal qualities in environments with vastly different acoustics, and it's the same with seeing consistent colors despite huge variations in source illumination, e.g., indoor vs outdoor. The processing required here is not trivial.

 

[natty]

Also hinted at is the argument that it is mistaken to think (or to want to) correct your room , like with REW that I keep permanently ready in my music room. The room is the room and you can't make it go away hoping to bring Carnegie Hall in instead. You can EQ the speakers and then, I suppose, you can bring in the recording engineer's workroom (or their earbuds). Does Uncle Jack sound different in you kitchen versus on the sidewalk?

This is interesting. My interpretation of his presentation of the data was the opposite.

The data he presents seems to make the case for using EQ in rooms for controlling room modes below the transition frequency, after setting up multiple subs with correct placement, since one doesn't hear the speakers (his words) below the transition frequency....rather, one hears "the room".

But yes, above the transition frequency, the data he collects about what people like leads him to the conclusion that in double blind testing, there was a consistent preference among a wide range of listeners in many different rooms to avoid EQ in favor of speakers that measure well in the CEA 2034 standard.

 

[AJ Soundfield]

You can EQ the speakers and then, I suppose, you can bring in the recording engineer's workroom

Star Trek fan??

 

[BenToronto]

A couple of great examples of how profoundly our brains construct our perceptions is how we can hear the same tonal qualities in environments with vastly different acoustics, and it's the same with seeing consistent colors despite huge variations in source illumination, e.g., indoor vs outdoor. The processing required here is not trivial.

Nicely put. The bits that your brain has to work with are really crap - nothing like "the eye is a camera" nonsense. All perception is creative construction. In that sense, Toole means that the brain tries to subtract the room in order to determine what the signal is, human or loudspeaker. Sometimes easy or not. Goal of acoustic treatment might be to make it easy. Likewise, good spinorama performance makes it easy. (But the alternative that I'd call "directivity-by-design" (as in Geddes speakers) may not?)

So with treble EQ, I think Toole would say what you are hearing is like you are changing the source and the source is almost inextricably a mingling of speaker and recording and just makes the Circle of Confusion worse.

natty is right to say bass is different. Perhaps humans in rooms don't have the cues to make bass veridical, a favourite psychology term of mine. I'm not sure if there is a conceptual difference between the improvement due to multi-subs compared to DSP EQ.

 

[natty]

'm not sure if there is a conceptual difference between the improvement due to multi-subs compared to DSP EQ.

The Welti research he quotes indicates there is a difference.

In it, multi subs or extreme tuned trapping appear to be the only way to get consistent bass for multiple listeners.

The EQ can then flatten response or introduce a custom curve.

Conceivably placement of multiple subs might obviate the need for much EQ.

The opposite approach (EQ without dual subs placed well): The data doesn’t seem to support this, except for careful placements of one sub + one listener position and the ability to eq for that one listening position (and likely very poor bass response elsewhere).

 

[Kal Rubinson]

Conceivably placement of multiple subs might obviate the need for much EQ.

It does as evidenced by experience in both my systems.

 

[johnp98]

I have posted a few questions on other forms after reading the book and wondering if people had any other thoughts:


1) Speaker positioning from the front wall and soundstage depth:
There was not too much discussion in terms of ideal positioning from the front wall outside of knowing about speaker boundary interference and adjacent boundary effects and how it will affect the bass response. It seems that bass response is the main consideration with positioning the speaker in/flush/in front/away from the front wall. Toole says “Adding absorption to the front wall, behind the loudspeakers, reportedly improved image localization and reduced coloration... Memo for Listening room recommendations: add sound absorbing material to front wall”

It seems the general audiophile advice is to pull speakers away from the front wall to help create a deeper soundstage etc yet I did not see this explicitly mentioned by Toole or Geddes. They seem to be ok with positioning the L&R speakers close to the front wall as long as one pays attention to bass response and possibly absorbs.

What I am wondering is if there truly is a benefit in soundstage depth with pulling the speakers away from the front wall?

Or do people think it is a psychoacoustic effect by having the front wall further away from the source (not saying that it is not a very real psychological effect, but merely one that cannot be seen on the frequency response, nor reproducible with blind tests)?

I wonder if this explains it: “Generations of listeners have noted the obvious differences in directional and spatial impressions created by sounds panned to the real left and right loudspeakers and those panned to intermediate positions, including center. The difference is that the extreme left and right locations are created by monophonic signals, delivered to single loudspeakers, whereas the intermediate image locations result from “stereo” signals, delivered to both loudspeakers simultaneously, with amplitude biases and/or delays appropriate to define the direction. The common impression is that the left and right panned sounds appear to originate in the loudspeakers themselves, whereas the intermediate images appear to originate further back, in a more spacious setting, and sometimes elevated. Instead of a soundstage extending across a line between the loudspeakers, the center images tend to drift back-ward.” - Toole

As then if the sound is hard panned to the L or R then it comes further forward (from the speaker), and then if intermediate positions then it appears higher up and further back and hence creates the impression of depth? Do people think that explains what we observe / hear?

What are peoples thoughts on the optimal distance from the front wall and imaging depth?

2) Speaker positioning from the side wall and side reflections:
Despite popular belief, it seems that the side wall reflections are important and desired. Specifically those that can come from wide angles (60°) as Toole writes “Start to think in terms of “preference,” “spaciousness,” “low interaural cross-correlation (IACC),” and “lateral reflections” as positively correlated with each other…. For maximum “preference” from the Ando (1977) data, it seems that reflections from about 30° to 90° are most effective. When IACC is measured, a broad minimum is seen around 60°, corresponding to a maximum in the preference ratings. Preference, therefore, is associated with low interaural cross-correlation….IACC exhibits a broad minimum around 60°.”
So should this goal of 60° determine the side wall distance goals? I think a lot of people would have a hard time getting 60° reflections from the near side wall but would be getting these angles from the far side wall.

Should we be setting up our speakers to ensure ~60° angle of the near wall reflections? If we do not have enough lateral room for this should this call into question the orientation of our rooms (having the width of the room be larger than the length if it allows for 60 angle reflection)?

3) Precedence Effect and side reflections
I am sure I just missed something somewhere when it comes to the precedence effect. But my understanding is that the primary sound will be heard first and that all reflected sounds will be combined into the first arriving sound. My understanding is that this is commonly misunderstood to mean that the delayed signals are ignored which is certainly not the case, as they are combined with the original signal, but that the original signal has all these other delayed signals added into the interpretation of it.

Toole mentions that delays greater than 30-40ms can then be interpreted as separate sources and thus everything under falls into the precedence effect does it not? So if the signals are being combined to that first signal, then does the distance of reflections matter? Does it matter if the side walls are mere inches vs feet vs meters away? Should it not all be interpreted under the primary signal? If that is the case, then would not all reflections in small rooms (under 30ms), be of no consequence when it comes to imaging? Once again, I am sure I am missing something here, but I like to think I understood that the delayed signal is combined with the original (and not ignored), but that the original signal trumps the delayed signal in terms of localization etc. But now it has me questioning the effects of all reflections and if they truly are damaging to soundstage.

4) Tooles low interaural cross-correlation (IACC) for imaging vs Geddes time intensity trading for image stability?
It seems like there are two opposing forces at play when it comes to toeing in of the speakers.

If you want truly low IACC and to isolate the L&R signals to the L&R ears (as used to the extreme with Ambiophonics or placing a mattress in between the speakers and up to your face) then one would not want to toe in the speakers to an extreme (at maximum aiming directly at the listening position, but probably further outward as ones off axis response allows). This should help with the soundstage and imaging. So I wonder if absorbing the far wall reflections (even though they are at a wider angle and thus less IACC, would help with soundstage would it not (although maybe at the cost of envelopment / spaciousness)

If you want a more stable “sweet spot” then using time intensity trading and aggressively toeing in the speakers as recommended by Geddes sure makes a lot of sense, and is easily experienced when I have personally done it. But is this improved sweet spot and image stability coming at the cost of a larger soundstage? I have not been able to definitively test this as I am not able to do blind tests myself, but I wonder what people impression is.

5) Finding the sweet spot:
I have never found an objective way to find the sweet spot for speakers until I read this from Toole:
“On the matter of the sound quality of the center phantom image in stereo, I recommend a simple experiment: Arrange for monophonic pink noise to be delivered to both loudspeakers. When seated in the symmetrical sweet spot, this should create a well-defi ned center image midway between the loudspeakers. If it does not, something is seriously wrong. If it does, consider what you hear as you lean very slightly to the left and to the right of the symmetrical axis. The timbre of the noise changes and more obviously the closer you sit to the loudspeakers. In fact, it is possible to fi nd the exact sweet spot by simply listening to when the sound is dullest. Moving even slightly left or right of the sweet spot causes the sound to get audibly brighter; there is more treble. It is much more exact to find the sweet spot by listening to the timbre change than by trying to judge when the center image is precisely localized in the center position. There is nothing faulty with the equipment or setup; this is simply stereo as it is—flawed…. Figure 9.7d shows the difference between the curves, revealing the result of acoustical interference. This can be confirmed by a simple calculation. The time differential between the ears for a sound source at 30° away from the frontal axis is about 0.27 ms for an average head. A destructive acoustical interference will occur at the frequency at which this is one-half of a period: 1.85 kHz. It won’t be a perfect cancellation because of a tiny propagation loss and a signifi cant diffraction effect. The wavelength is just over 7 in. (178 mm), which, because it is similar in dimension to the head, will experience a substantial head-shadowing effect at the ear opposite to the sound source. There will be an interaural amplitude difference of the order of 6 dB in this frequency range”

Does this seem like the best way to find and judge the sweet spot in ones room?

In the past I have also used repeating short clips from songs recorded in QSound (I have taken a few seconds from the openings to a song in Amused to Death and made a loop on perpetual repat and then inverted the R&L channels to test each speaker and its positioning). Has anyone else tried something similar or what do people think is the best way to test imaging (outside of grossly assessing soundstage from well-known songs)?

If anyone wants to chat and discuss any of the above topics that would be much appreciated!
Thanks!

 

[Kal Rubinson]

It seems the general audiophile advice is to pull speakers away from the front wall to help create a deeper soundstage etc yet I did not see this explicitly mentioned by Toole or Geddes.

I think of it as a practice that subconsciously co-opts visual bias.

 

[FargateOne]

About how far away from the front wall speakers must be, I recently push back my speaker from 55cm (as recommanded and measured from the back of the speaker as recommanded by the manufacturer) to 30cm to avoid bad SBIR effect. When I found the right toeing ( using pink noise full range in stereo and reverse polarity of one speaker) I found that SS&I and deep sound stage are quite the same. Unfortunatly I can't put the fronts far away the front wall ( 1 meter or more) to hear the difference.

 

[natty]

1. The closer to the front wall the less problematic sbir is in the sense that you can absorb the sbir with conventional thick acoustic panels if the speakers are a matter of inches off the front wall. Further away than that and the wavelengths get too long for normalmfour to six inch deep panels.

2.3.4. This depends a bit on the speakers and how their off axis response works but a speaker that does will with CEA 2034 (the spinorama) can create a very wide soundstage via the first reflection points even when toed in toward the listener to create a very precise center image.

5. I prefer a mono signal for testing this though more and more if toe in direct toward the main listening seat doesn’t work, I’ll likely not continue to use a speaker, since I run a multichannel rig and the center (identical to the left and right speaker) is inevitably pointed directly at me, so I prefer speakers that allow that on the left and right as well.

 

[mechtheist]

...
natty is right to say bass is different. Perhaps humans in rooms don't have the cues to make bass veridical, a favourite psychology term of mine. I'm not sure if there is a conceptual difference between the improvement due to multi-subs compared to DSP EQ.

veridical:

• truthful
• coinciding with reality

A very useful term. It's sad that 2nd definition isn't considered a desirable goal by an awful lot of folks these days, or maybe more accurately, they quite adamantly believe their subjective experience coincides with reality.

Perhaps the difference with bass is due to how you really are hearing the room, the direct sound heard isn't the majority of the sound energy present, the reflected sound/resonances and standing waves dominate. It could be beyond our brain's computational capability to compensate, possibly lack of cues could certainly play a part--too many unknown variables for the number of equations needing solving. I don't know about you but it's not a habit of mine to go into a room I haven't visited before and wander about while chirping. From an evolutionary standpoint, I can understand color compensation, every day the source illumination goes through a huge variation, that circuitry almost certainly predates humans and probably even homo by a large margin, but where did the need for acoustic compensation come from? Cave life? Humans primarily evolved in savanna environments. Did it arise due to a need for speech recognition or something more basic? Maybe wildly off-topic but not necessarily so.

4 years ago, I left a similar comment on Toole's Sound reproduction – art and science/opinions and facts video, he replied:

Yes, I use the visual color temperature analogy regularly. Cameras record differences between sun and shade, incandescent and fluorescent, etc. but humans adapt on the fly. There are limits to adaptation, though, and in light eventually we will recognize and possibly be annoyed by a pronounced color shift. In audio, most of the perceptual differences between rooms are due to resonances/standing waves at bass frequencies. These cause coloration - "booms" - and large seat-to-seat variations. There are solutions to both but they involve measurements, multiple subwoofers and some signal processing. At middle to high frequencies, if you begin with a well-designed loudspeaker (flattish and smooth on axis and relatively constant directivity) the room is rarely a problem. Humans adapt, by separating the sound of the source from the sound of the room - up to a point: there is a limit to what we can adapt to. But normally furnished domestic rooms are often excellent listening spaces. The parallel to this is live musical performances, where voices and musical instruments maintain very constant timbral signatures in different concert venues. We are aware of subtle details in the sound sources, even though the venue sounds may be different. Several investigations indicate that there is a significant improvement in speech intelligibility if listeners have only a few minutes to become familiar with the venue. It would be rational to think that there is a similar improvement in perception of details in music, or of recognizing defects in loudspeakers reproducing music. Tests have shown this to be true.

 

[Marc Lombardi]

It does as evidenced by experience in both my systems.

Placement, treatment, correction ... in that order, right? And adding subs (at least up to four) has been shown to have very good effect. The amount of correction needed in my system is far less today than it was several years ago ... after adding a sub, changing position, adding bass traps. Dirac Live adds the finishing touch.

Another option that is rarely if ever considered is different drivers to fill in mid-bass dips. In other words, not just two or four subs capable of plumbing the depths of the 32' rank, but a couple of small woofers playing in the 50-150Hz range. Driven with the sub signal, placed independently from the main speakers and subs, to fill in dips at maybe 60Hs or 120Hz. This also makes some sense as we add smaller surrounds and Atmos tops that may need to cross over higher than the usual 80Hz sub limit.

I do this with Magnepan 3.7's and DWM's .... anyone else do something like this?

 

[Marc Lombardi]

1. The closer to the front wall the less problematic sbir is in the sense that you can absorb the sbir with conventional thick acoustic panels if the speakers are a matter of inches off the front wall. Further away than that and the wavelengths get too long for normalmfour to six inch deep panels.

2.3.4. This depends a bit on the speakers and how their off axis response works but a speaker that does will with CEA 2034 (the spinorama) can create a very wide soundstage via the first reflection points even when toed in toward the listener to create a very precise center image.

1 - Pretty tough for a four to six inch thick absorber against a wall to have much affect on bass below 200Hz though. Absorbers work best at quarter wavelength from the reflecting surface, so even at 200Hz that's 1.4ft.

2,3,4 - Has anyone tried aiming the speaker directly at the first reflection point such that the bounce ends up at the MLP? Sometimes called the "Rooze" setup by us planar dipole-philes.

 

[AJ Soundfield]

It seems the general audiophile advice is to pull speakers away from the front wall to help create a deeper soundstage etc

Never listen to audiophiles.
That said, as Kal noted you have a single CPU for multi-sensory real life. No denying visual cues and expectations can play into perceived, I personally find closing eyes makes "depth" largely disappear. Others possibly not. Anecdotal. However, the durations and angles of the reflections do affect the perception, so even in mono blind listening, one can perceive different "depth" based on the speakers polar pattern. But there is also the fact that when you pull speaker further into the room as suggested, you increase the direct/reflected ratio because the speakers are closer to you/further from side/front walls (with typical fixed directivity speakers).
And then there is preference, AV variety...

cheers

 

[natty]

1 - Pretty tough for a four to six inch thick absorber against a wall to have much affect on bass below 200Hz though. Absorbers work best at quarter wavelength from the reflecting surface, so even at 200Hz that's 1.4ft.

I'm not sure I follow your reasoning here. I could be missing someithng. I'm still learning.

Near as I can tell, six inches of owens corning 700 series has greater than a 1.0 absoroption coefficient down at 125hz. http://www.bobgolds.com/AbsorptionCoefficients.htm

But it isn't necessary to get that low, right? At least not always.

I mean if the speaker baffle is 15 inches off the front wall, the quarter wavelength SBIR issue happens at about 200hz, right? (http://www.procato.com/calculator-wavelength-frequency/)

Which should be pretty easy to completely kill with a single panel right behind the speaker, right? In fact if we believe the specs, a 3" panel would suffice since it had an absorption coefficient over 1.0 at 200hz...but since some/many speakers are a little too deep to place the front baffle that close to the wall, a thicker panel is a safer bet.

Speaker Placement 101: Is Speaker-Boundary Interference Killing Your Bass?

Not hearing enough bass through your monitors? The distance between your room boundaries and speakers has a huge impact on your bass performance. This tutorial will show you specific strategies for placing your speakers to get a balanced bass response.

arqen.com

 

[FargateOne]

About toeing the fronts, the best and easiest way I discover is the following forom a member Linearphase:
linearphase said:


3. Tweak the toe in and MLP to produce the best sound and most lifelike imaging. Keep things very symmetrical. if you have access to pink noise you can also play it over both speaker to confirm a good centered image. Then reverse the leads on ONE speaker. You should hear a "hole" between the speakers with the rest of the sound speed evenly out from there, ideally extending even bit outside the speakers. Tweak the toe in while at the listening position slightly. You should find one position were the noise sounds smooth AND the image just locks to a hole in the center. Don't forget to return the leads back to normal polarity when done here.

It is the second step that make a differnece (the whole in the center after reverse polarity of one speaker) which is more difficult to find but when you got it, the SS&I is better.

 

[Marc Lombardi]

I'm not sure I follow your reasoning here. I could be missing someithng. I'm still learning.

Near as I can tell, six inches of owens corning 700 series has greater than a 1.0 absoroption coefficient down at 125hz. http://www.bobgolds.com/AbsorptionCoefficients.htm

But it isn't necessary to get that low, right? At least not always.

I mean if the speaker baffle is 15 inches off the front wall, the quarter wavelength SBIR issue happens at about 200hz, right? (http://www.procato.com/calculator-wavelength-frequency/)

Which should be pretty easy to completely kill with a single panel right behind the speaker, right? In fact if we believe the specs, a 3" panel would suffice since it had an absorption coefficient over 1.0 at 200hz...but since some/many speakers are a little too deep to place the front baffle that close to the wall, a thicker panel is a safer bet.

Speaker Placement 101: Is Speaker-Boundary Interference Killing Your Bass?

Not hearing enough bass through your monitors? The distance between your room boundaries and speakers has a huge impact on your bass performance. This tutorial will show you specific strategies for placing your speakers to get a balanced bass response.

arqen.com

I may be wrong. But I've read that "resistance" absorbers like 703 are "velocity" based, and so have their greatest effect where velocity is the greatest. Velocity is zero at the wall (pressure is at its max at the wall). Velocity is greatest at the quarter wavelength of the frequency in question. Maybe it's more relevant in absorbing modal resonances than a first reflection of the low frequency wave from the speaker. But then below the transition frequency, and steady state, how would we distinguish first reflection from modal resonance? The answer is .... it should be measurable, right?

 

[Sonnie Parker]

I've had what I believe is good success starting out with the speaker placement recommendations by Cardas: http://www.cardas.com/room_setup_main.php

It was not until I tried those recommendations many years ago that I actually started enjoying listening to music. The closer I am to the speakers, the better it sounds to me... and the depth is beautiful.

Whether to treat the front wall with absorption or diffusion also depends on the speakers... as it is my understanding that planar speakers like MartinLogan should have the front wall diffused.

Having said all that, now that I've read a good bit of Toole's book (and references to parts I have yet to read), I'm not sure what I am hearing is real or fake anymore... perhaps my mind has been playing a lot of tricks on me.

 

[Marc Lombardi]

I've had what I believe is good success starting out with the speaker placement recommendations by Cardas: http://www.cardas.com/room_setup_main.php

It was not until I tried those recommendations many years ago that I actually started enjoying listening to music. The closer I am to the speakers, the better it sounds to me... and the depth is beautiful.

Whether to treat the front wall with absorption or diffusion also depends on the speakers... as it is my understanding that planar speakers like MartinLogan should have the front wall diffused.

Having said all that, now that I've read a good bit of Toole's book (and references to parts I have yet to read), I'm not sure what I am hearing is real or fake anymore... perhaps my mind has been playing a lot of tricks on me.

With my Magneplanar 3.7's I started with the Cardas recommendations and went from there. I tried a lot of absorption initially with 3" Sonex on the front wall and up the sides, then when diffusers of various types became available I experimented with some thin 1D diffusers initially and from that point on the absorption came down and more diffusers went up. I settled on the Vicoustic Multifuser and have lots of them on the front wall and four feet up the sides. When Wendell Diller did his 30.7 North America demo tour a couple years ago he said the best sounding rooms had lots of diffusion.

A controversial thing in the book is the discussion of absorption/diffusion/reflection at the first reflection points, especially the side walls. I really think this depends on the distance to the side walls as well as the type of speaker. In a narrow room (mine is 13ft) I tried all three and imaging was best with absorption. But if the room is wide enough the distance that the first reflection travels is long enough that Haas Effect may overwhelm the reflection and imaging could be fine. I've read that a room width starting at 17ft would have this effect.

One thing Toole points out is that you can get used to the sound of a room and your brain will fill some things in. The room truly may sound different to the owner than to someone who is unfamiliar.

 

[natty]

And, as you note, much of what he wrote about sidewall reflections is in the context of speakers that measure well in particular ways such as linearity, and smooth off axis response, which means that a Magnepan (at least the ones I have owned) are not the kind of speakers he is talking about.

 

[Marc Lombardi]

And, as you note, much of what he wrote about sidewall reflections is in the context of speakers that measure well in particular ways such as linearity, and smooth off axis response, which means that a Magnepan (at least the ones I have owned) are not the kind of speakers he is talking about.

Right, he rarely mentions dipoles other than to say YMMV with them. In particular I recently read a comment like that where he was discussing the listening tests from which the proverbial Harman Curves were derived. Of course those tests were done with conventional box speakers, and I might add, commercial studio recordings of pop music (i.e. no classical or jazz recorded in live settings). I mention the latter because it seems pointless to me to discuss imaging and soundstage for recordings made with a number of close mic'ed instruments in a studio (perhaps even on different days), such that there is no "there" there, and then "mastered" to the point that all hint of dynamics has been pounded flat. Did I just digress?

 

[natty]

I would love to see the reference to the recordings used in some of the testing. I've never been able to find that information.

 

[AJ Soundfield]

In particular I recently read a comment like that where he was discussing the listening tests from which the proverbial Harman Curves were derived. Of course those tests were done with conventional box speakers, and I might add, commercial studio recordings of pop music (i.e. no classical or jazz recorded in live settings).

Link?
FYI, you do know he tested (at NRC), was suitably impressed and owned Bipolar speakers, prior to his forward firing Salons, yes?
They also tested Quads and at least one, older ML.

cheers