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Horns - Necessary to complete the Audiophile Journey?

Duke

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Would it be accurate to assume that the M2 waveguide "pinches" the waveform in the horizontal and vertical plane? It looks like two sets of fingers is pinching the mouth.
I think those "fingers" gently introduce diffraction, which actually widens high frequency coverage in those directions. But arguably most of the sound from the compression driver goes in between the fingers, and it is not clear to me what the radiation pattern looks like in those directions (especially along the diagonals). Listening tests have confirmed that the M2 is superb, so whatever happens at other angles is obviously not a problem. It also looks to me like that waveguide's geometry avoids detrimental internal reflections. And if there are any, I don't think they would be in the direct sound - I think they'd careen off in harmless directions. Kudos to Charles Sprinkle!

I remember reading somewhere that Charles Sprinkle no longer believes in constant directivity as the best solution and that he now thinks smooth but steadily rising directivity is preferable. I asked directly and he said it had a lot to do with needing a high-shelf filter from around 2khz with the JBL M2 in normal/small rooms to sound natural that led him onto that path.
VERY INTERESTING that Sprinkle finds (presumably gently) rising directivity to be preferable to a gently downward-shelved direct sound (with constant directivity) in a small room. Thank you for passing that along.

The approach I use is constant directivity but with a gently downward-tilting direct sound, instead of a "flat" direct sound. In my opinion this gives a natural-sounding tonal balance while minimizing the spectral discrepancy between the direct sound and the reflections, which in turn is arguably beneficial to timbre. My designed-for listening axis is about 20 degrees off the horn's centerline (after Geddes), so there is some tilt-down of the highs in the direct sound already happening. The horn's inevitably slightly "hotter" on-axis energy is actually making its first appearance at the central "sweet spot" as reflected sound, thereby tipping the spectral balance of the reverberant field up a bit, which reduces the net discrepancy between it and the direct sound.

Of course I realize this goes against Harman's findings of what listeners prefer (flat on-axis, tilt-down off-axis), and unfortunately for my credibility, it also goes against what Charles Sprinkle now believes to work best. Hmmm. Don't tell my marketing department, they'll demand a bigger budget.

I have JBL M2's now and had Kii Three previously, both more or less constant directivity designs. Can't say I feel they suffer from it. Is this perhaps one of the more academic discussions where the issue is solved by somewhat different tuning?
I tried working with the tweeter Kii uses years ago, back before the Kii Three came out. Measurements were superb, but I heard a slight edginess in the sound which imo became distracting at high levels, and nothing in my measurements explained it. [speculation] The diffraction introduced by the fingers in the Sprinkle waveguide is incoherent enough to be perceptually benign, while the diffraction introduced by the sharp edges between the concentric flat rings in the Kii tweeter's waveguide is coherent enough to not be. [/speculation]
 
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Absolute

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I think those "fingers" gently introduce diffraction, which actually widens high frequency coverage in those directions. But arguably most of the sound from the compression driver goes in between the fingers, and it is not clear to me what the radiation pattern looks like in those directions (especially along the diagonals). Listening tests have confirmed that the M2 is superb, so whatever happens at other angles is obviously not a problem. It also looks to me like that waveguide's geometry avoids detrimental internal reflections. And if there are any, I don't think they would be in the direct sound - I think they'd careen off in harmless directions. Kudos to Charles Sprinkle!

VERY INTERESTING that Sprinkle finds (presumably gently) rising directivity to be preferable to a gently downward-shelved direct sound (with constant directivity) in a small room. Thank you for passing that along.

Of course I realize this goes against Harman's findings of what listeners prefer (flat on-axis, tilt-down off-axis), and unfortunately for my credibility, it also goes against what Charles Sprinkle now believes to work best. Hmmm. Don't tell my marketing department, they'll demand a bigger budget.
I think it makes sense that they usually ended up with a high-shelf filter at around 2 khz about -0,5 to -1 dB gentle slope in normal rooms because it looks like the M2 has a small rise in sound power from 2-7 khz based on the spin. That could be one explanation, the other could be that it's better with a flat on-axis response and a little bit downwards-tilted listening window response.
It could also be a combination of both.

Spin - JBL M2 (full spin).png



Anyways, it's possible that this is one of those things where assumptions are made about cause and effect that are generally just a guesstimate, even by Mr. Sprinkle himself.

When we used to tune the M2 in rooms, we would usually put in a high shelf at around 2kHz, -0.5 to -1dB with a gentle slope to get it to sound right. This is one of the data points that led me to the conclusion of a smooth DI.
I tried working with the tweeter Kii uses years ago, back before the Kii Three came out. Measurements were superb, but I heard a slight edginess in the sound which imo became distracting at high levels, and nothing in my measurements explained it. [speculation] The diffraction introduced by the fingers in the Sprinkle waveguide is incoherent enough to be perceptually benign, while the diffraction introduced by the sharp edges between the concentric flat rings in the Kii tweeter's waveguide is coherent enough to not be. [/speculation]
I really enjoy your contributions and posts here, Duke. You really enrich this forum with your presence and fantastic personality and I appreciate your willingness to share your knowledge left, right and center! Thank you for that.

About that Kii driver; I've heard the same thing from different DIY builders that they just couldn't get rid of that edginess/harshness no matter what. I struggled with that also and suspected a resonance around 3-4 khz as I mentioned earlier. For me it wasn't a problem at normal listening levels because I live in an apartment and usually listen to music at around 65-70 dB. With a downwards tilted slope it didn't rear its head before going stupid loud, and I'm not even sure I'm on the correct diagnosis. Could be ringing from the stands for all I know, so I won't discourage people from trying Kii because they're fantastic speakers.

The approach I use is constant directivity but with a gently downward-tilting direct sound, instead of a "flat" direct sound. In my opinion this gives a natural-sounding tonal balance while minimizing the spectral discrepancy between the direct sound and the reflections, which in turn is arguably beneficial to timbre. My designed-for listening axis is about 20 degrees off the horn's centerline (after Geddes), so there is some tilt-down of the highs in the direct sound already happening. The horn's inevitably slightly "hotter" on-axis energy is actually making its first appearance at the central "sweet spot" as reflected sound, thereby tipping the spectral balance of the reverberant field up a bit, which reduces the net discrepancy between it and the direct sound.
This approach certainly sounds logical based on what Mr. Sprinkle says and my own findings with both Kii and M2, especially in a smaller reflective room like we usually have here in Europe.
Intuitively it makes sense to have different tonal balance depending on the direct vs reflective sound ratio, but this is speculation on my part.

If a nice compromise is to be made in a passive speaker, I'd rather have a dB too much downward tilt than the opposite :D
 

tuga

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The approach I use is constant directivity but with a gently downward-tilting direct sound, instead of a "flat" direct sound. In my opinion this gives a natural-sounding tonal balance while minimizing the spectral discrepancy between the direct sound and the reflections, which in turn is arguably beneficial to timbre. My designed-for listening axis is about 20 degrees off the horn's centerline (after Geddes), so there is some tilt-down of the highs in the direct sound already happening. The horn's inevitably slightly "hotter" on-axis energy is actually making its first appearance at the central "sweet spot" as reflected sound, thereby tipping the spectral balance of the reverberant field up a bit, which reduces the net discrepancy between it and the direct sound.
Have you experimented with the frequency where transitioning from narrow to wide takes place?
What would be the sweet spot in your opinion, 300Hz too high or perhaps low enough?
How steep is that transition in your best effort?

I would really like to listen to one of your designs but I don't think that they're that common in the UK, or Geddes for that matter.
 

tuga

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I really enjoy your contributions and posts here, @Duke . You really enrich this forum with your presence and fantastic personality and I appreciate your willingness to share your knowledge left, right and center! Thank you for that.
I second that!
 
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watchnerd

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Wish I didn't have all the back issues I do, I'd love to go handgun hunting for them.
When boar hunting, I carry a side arm (S&W 586 6" .357 mag), but I've only had to use it once in an emergency.

I use a Remington 700, chambered for .308 Winchester, as my rifle.

168 gr "Hog Hammer" / Barnes TSX ammo.
 
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Duke

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I really enjoy your contributions and posts here, Duke. You really enrich this forum with your presence and fantastic personality and I appreciate your willingness to share your knowledge left, right and center! Thank you for that.
Thank you very much, it's an Absolute pleasure. But any sociopath worthy of the title can talk a good game.

And if I seem overly optimistic about the alleged merits of what I do, that comes with the territory. The only people left in this industry are the optimists.

Have you experimented with the frequency where transitioning from narrow to wide takes place?
I assume you are talking about the transition between omnidirectional bass and directional mids/highs? Basically what I do is let the midwoofer's diameter dictate the transition region at it starts to beam, and then cross over to the constant-directivity horn where the woofer's pattern has narrowed to match the horn's.

You can see this sort of thing going on in the M2's curves posted by Absolute in Post #382 above. The 15" woofer's pattern actually starts narrowing at about 100 Hz, and continues to do so until the crossover region, ballpark 800 Hz or so. Then the directivity index flattens out until we get to about 7 or 8 kHz.

What would be the sweet spot in your opinion, 300Hz too high or perhaps low enough?
Imo the IDEAL would be, to maintain the same radiation pattern width all the way up and down the spectrum. The non-omnidirectional speakers which comes the closest to this are, to the best of my knowledge, the big SoundLab fullrange electrostats in the original (90 degree pattern width, front and back) configuration. Imo they do a great many other things right along the way. Their off-axis frequency response is identical to their on-axis frequency response (there is no "hot spot" in the middle of that 90 degree arc), and the curve for both is gently downward-sloping by about 3 dB per decade, or at least that's my recollection from watching them run quality-control curves at their factory.

I have not opted for a dipole enclosure because of the minimum distance-from-the-wall requirements (imo 5 feet/1. 6 meters), nor for a cardioid because I want good response all the way down to at least 80 Hz (where a distributed multisub system can take over). And either of these approaches would call for custom T/S parameters, unless I'm willing to forego a lot of efficiency.

An arguably reasonable "real world target" is 700 Hz for the top-end of the transition region, i.e. crossover to the waveguide, as according to researcher David Griesinger the region from 700 Hz to 7 kHz is where the ear/brain system gets most of its information from. I don't know that Griesinger's research informed the design of the JBL M2, but they did an imo superb job in that specific region, as that's where their directivity index is flat.

How steep is that transition in your best effort?
The steepness of the directivity index transition from omnidirectional (down low) to the crossover region would probably be the same as what you see in the directivity of the M2, but scaled to the much smaller midwoofer diameter of my thus-far "best effort", which uses a 10" midwoofer. Larger variations on the theme are in the pipeline.

Also, I have yet to do any two-ways with a crossover as low as the M2's 800 Hz because thus far I have been using small-format (1" throat) compression drivers, but I am having waveguides for 1.4" throat compression drivers made. Depending on what the actual measurements say, I may end up with an 800 Hz ballpark crossover frequency.

(I'm not trying to copy the M2. My speakers will have considerably narrower directivity from their front-firing waveguide than the M2 does, then the reverberant field will be augmented by rear-firing drivers. So imagine Amar Bose being on the team that designed the M2...)

I would really like to listen to one of your designs but I don't think that they're that common in the UK, or Geddes for that matter.
I'm afraid not! I know Earl shipped some Summas to continental Europe, and I have some speakers in Asia, but I don't think either of us has anything in the UK.

I hope to get something from my forthcoming generation into Amir's hands, which arguably might be the "next best thing" to an audition. We've had a very preliminary conversation about it and thus far the hurdles seem surmountable. Unfortunately recent manufacturing setbacks to delivery of a critical piece of the puzzle makes my timeframe uncertain.
 
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The M2 Waveguide is basically a modern take on JBL's (Keele's) Bi-Radial horns. There's a diffraction slot at the throat - which includes the 'knuckles'.
The 'cheeks' provide additional (path) length and facilitate both wide coverage + reduced edge diffraction/reflection.
Earl Geddes primarily perceives it as an interesting-looking object with some marketing speak to support it, but nothing revolutionary. I tend to agree.
People who compared the M2 wg to the latest PT-horns (with the same drivers) have found the differences in perceived sound quality to be negligible and the PT-horns much easier to work with.
 
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Duke

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People who compared the M2 wg to the latest PT-horns (with the same drivers) have found the differences in perceived sound quality to be negligible and the PT-horns much easier to work with. [emphasis Duke's]
I'm not familiar with JBL's "latest PT [Progressive Transition] horns"... can you give me a model number or two, so I can look at the right ones?

And in what way are they "much easier to work with", if you don't mind?

I'm not up to speed on JBL horns, sorry.

Thanks!
 
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For those who'd like to try cheap PA speakers that sound decent, I suggest to score a pair of used JBL 'install' speakers, like the AC- and AE-series.
While the drivers in the AC-series are still mediocre, at least the cabinets are better built than the plastic EON boxes.
Recently I heard these in a restaurant and was pleasantly surprised. Just don't expect any (sub) bass.

AC2212_95.png



Another option is the previous Yamaha DXR, DXS, DSR series (active).

DXR Series.jpg
 
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I'm not familiar with JBL's "latest PT [Progressive Transition] horns"... can you give me a model number or two, so I can look at the right ones?

And in what way are they "much easier to work with", if you don't mind?

I'm not up to speed on JBL horns, sorry.

Thanks!

Here are (just) 2:

JBL #5006815 for STX825 (90° × 50° nominal):

1.5WG.PNG



JBL #5006219 for STX815 (70° × 70° nominal):

1.5WG2.PNG



Both are 1.5" exit and I expect the BMS 4555 to work well with either.


As regards to the M2 versus the STX waveguides, here's a comment of a JBL adept, who uses both:

"I would argue that it is not worth to go for M2 horns. The VTX horns behave very well and are easier to equalize."

More info can be found on the heritage forum.
 
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Duke

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Here are (just) 2:

JBL #5006815 for STX825 (90° × 50° nominal):

View attachment 73943


JBL #5006219 for STX815 (70° × 70° nominal):

View attachment 73944


Both are 1.5" exit and I expect the BMS 4555 to work well with either.


As regards to the M2 versus the STX waveguides, here's a comment of a JBL adept, who uses both:

"I would argue that it is not worth to go for M2 horns. The VTX horns behave very well and are easier to equalize."

More info can be found on the heritage forum.
Thank you VERY MUCH! Headed over to Lansing Heritage now...
 
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watchnerd

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For those who'd like to try cheap PA speakers that sound decent, I suggest to score a pair of used JBL 'install' speakers, like the AC- and AE-series.
While the drivers in the AC-series are still mediocre, at least the cabinets are better built than the plastic EON boxes.
Recently I heard these in a restaurant and was pleasantly surprised. Just don't expect any (sub) bass.

View attachment 73938


Another option is the previous Yamaha DXR, DXS, DSR series (active).

View attachment 73939
Are those passive?
 

Sal1950

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I really enjoy your contributions and posts here, Duke. You really enrich this forum with your presence and fantastic personality and I appreciate your willingness to share your knowledge left, right and center! Thank you for that.
+1, Learning a lot from you Duke, thanks for all your contributions to ASR!

I use a Remington 700, chambered for .308 Winchester, as my rifle.

168 gr "Hog Hammer" / Barnes TSX ammo.
I've got a beautiful S & W 460 magnum with a 5" barrel, I'd love to take a hog with it. I hand load all my own ammo and could cook up a round that would drop him like a sack of potatoes. It would be nice to have you behind me with that Remington "just in case" LOL
 
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The approach I use is constant directivity but with a gently downward-tilting direct sound, instead of a "flat" direct sound. In my opinion this gives a natural-sounding tonal balance while minimizing the spectral discrepancy between the direct sound and the reflections, which in turn is arguably beneficial to timbre. My designed-for listening axis is about 20 degrees off the horn's centerline (after Geddes), so there is some tilt-down of the highs in the direct sound already happening. The horn's inevitably slightly "hotter" on-axis energy is actually making its first appearance at the central "sweet spot" as reflected sound, thereby tipping the spectral balance of the reverberant field up a bit, which reduces the net discrepancy between it and the direct sound.

Of course I realize this goes against Harman's findings of what listeners prefer (flat on-axis, tilt-down off-axis), and unfortunately for my credibility, it also goes against what Charles Sprinkle now believes to work best. Hmmm. Don't tell my marketing department, they'll demand a bigger budget.
Duke, I wonder if you may be a tiny bit off in your summary of Harman's findings. Since Sean Olive's prediction model was published, I personally believe that the Revel speakers have been actually designed for flatter listening window than on-axis measurements, based on Kevin Voeck's (@AVKV) comments ((https://www.avsforum.com/forum/89-speakers/710918-revel-owners-thread-408.html#post56177990): "As our research has long indicated, the listening window is a far better indicator of direct sound quality than is any on-axis curve. On-axis curves measured from just slightly different microphone locations will yield different results at high frequencies due to trivial local diffraction, making them misleading. The listening window greatly mitigates this problem."), as well as multiple measurements from Harman (https://speakerdata2034.blogspot.com/2019/03/spinorama-data-revel-home.html) and ASR showing that the listening window curves tend to be smoother than the on-axis ones for the Revel speakers, as well as the JBL M2 also shows a flatter listening window than the "hotter" on-axis treble. Also, the ASR estimated in-room response curves for the M105 and M106 show a bump around 4-6 kHz that's much more reflective of the LW than OA curves, which goes along with this.

Others have analyzed the preference model much more thoroughly than I can hope to ever do, but my impression was that smoothness, but not slope, of the sound power and other curves mattered. If I recall correctly, Toole has commented on constant or at least smoothly changing directivity in his various writings. Consequently, the Harman approach seems to have resulted in more than one approach, since it has produced the JBL Array 1400 which I regard in some ways as an earlier, more extreme version of the M2 in its relatively constant but very high directivity and flattish sound power above 800 Hz, then the M2 with flatter sound power and directivity, though not as high.

Also, there seemed to be different types of listeners with different preferences for steady state room curves:
Screen Shot 2020-07-18 at 12.29.55 AM.png
Toole, with his usual caution, writes "To date there is some evidence of agreement that the target curve should exhibit a downward slope over at least a portion of the frequency range."I thought it was interesting that the predicted steady state curve for the flat direct sound was also pretty flat above 2 kHz.

He also writes "The attenuated high frequencies preferred by the trained listeners stands in contrast to the preferences exhibited by those same listeners in numerous double-blind multiple-comparison loudspeaker evaluations. In those tests, it is the flat on-axis loudspeakers that are most highly rated (those that perform close to the predicted curve in Fig. 14). Is this a consequence of the different experimental methods: the different listener tasks? In one, listeners adjusted the bass and/or treble balance in a single loudspeaker model; in the other they rated spectral balances and other attributes in randomized comparisons of different products. It is a subtle but important difference awaiting an explanation."

From what little I understand, the double-blind loudspeaker evaluations were done using single (mono) speakers in the multichannel listening lab, which highly emphasizes direct sound (https://www.harman.com/documents/HarmanWhitePaperMLLListeningLab_0.pdf: "In the MLL room, the only significant first order reflections are from the floor, and these are attenuated at higher frequencies by the carpet. At listener-loudspeaker distances greater than 2 m any reflection with a path length greater than 6.34 m will be attenuated 10 dB by spreading loss [18]. This effectively eliminates all second order reflections since their path length exceeds this value")

On the other hand, the target curve preference test (https://www.innerfidelity.com/content/acoustic-basis-harman-listener-target-curve) was done using stereo speakers in a different, more reflective room (http://seanolive.blogspot.com/2009/05/harman-international-reference.html).

It occurs to me that some of the differences in preference may be in part a result of more room reflections and possibly stereo listening...

Anyway, I got off on a tangent, so good night.

Young-Ho
 

Duke

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Duke, I wonder if you may be a tiny bit off in your summary of Harman's findings....
You are absolutely correct!!

Thank you very much for catching that, and for taking the time to educate me with such a thorough post. I'm about 1/3 of the way through your links as I type this.

I think you are onto something with the relative lack of strong reflections in Harman's single-speaker auditions, but I need to read your links first.
 

tuga

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Imo the IDEAL would be, to maintain the same radiation pattern width all the way up and down the spectrum. The non-omnidirectional speakers which comes the closest to this are, to the best of my knowledge, the big SoundLab fullrange electrostats in the original (90 degree pattern width, front and back) configuration. Imo they do a great many other things right along the way. Their off-axis frequency response is identical to their on-axis frequency response (there is no "hot spot" in the middle of that 90 degree arc), and the curve for both is gently downward-sloping by about 3 dB per decade, or at least that's my recollection from watching them run quality-control curves at their factory.

I have not opted for a dipole enclosure because of the minimum distance-from-the-wall requirements (imo 5 feet/1. 6 meters), nor for a cardioid because I want good response all the way down to at least 80 Hz (where a distributed multisub system can take over). And either of these approaches would call for custom T/S parameters, unless I'm willing to forego a lot of efficiency.

An arguably reasonable "real world target" is 700 Hz for the top-end of the transition region, i.e. crossover to the waveguide, as according to researcher David Griesinger the region from 700 Hz to 7 kHz is where the ear/brain system gets most of its information from. I don't know that Griesinger's research informed the design of the JBL M2, but they did an imo superb job in that specific region, as that's where their directivity index is flat.
I was asking in the context of a waveguided speaker.
With multi-way multi-horn speakers you can take it very low.
I haven't see measurements for Avantgrade's Trio w/ Bass Horns or even for the Duo so here's one for the Uno XD (which cannot avoid the glitch at 3kHz because it has unsificient number of ways):




Edit: the M2 for comparison

 
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tuga

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The steepness of the directivity index transition from omnidirectional (down low) to the crossover region would probably be the same as what you see in the directivity of the M2, but scaled to the much smaller midwoofer diameter of my thus-far "best effort", which uses a 10" midwoofer. Larger variations on the theme are in the pipeline.

Also, I have yet to do any two-ways with a crossover as low as the M2's 800 Hz because thus far I have been using small-format (1" throat) compression drivers, but I am having waveguides for 1.4" throat compression drivers made. Depending on what the actual measurements say, I may end up with an 800 Hz ballpark crossover frequency.

(I'm not trying to copy the M2. My speakers will have considerably narrower directivity from their front-firing waveguide than the M2 does, then the reverberant field will be augmented by rear-firing drivers. So imagine Amar Bose being on the team that designed the M2...)
That sounds interesting but are you going for a 2- or a 3-way speaker? Would it be a Gina and a Super Stand in a single speaker?

A 3-way would also potentially lower THD and IMD.
I wonder if the preference for the Ultima Salon2 over the M2 could partly have been due to the former being a 4-way.

From a conceptual point of view I would like a speaker with a driver doing the bass duties, a midrange driver to cover the mids and another for the high frequencies. Sub-bass would ideally require a dedicated driver or the speaker could be assisted by subwoofers but I've lived hapilly with a large 3-way. In essence a 4-way or a 3-way + sub. Preferably all sealed or if ported with very low tuning.

My reference 3-way is a friend's B&W 801F (brochure attached). It's got a 12" woofer in a large sealed bass bin and it plays bowed or plucked orchestral double bass and tympany with a mesmerising clarity.
 

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You are absolutely correct!!

Thank you very much for catching that, and for taking the time to educate me with such a thorough post. I'm about 1/3 of the way through your links as I type this.

I think you are onto something with the relative lack of strong reflections in Harman's single-speaker auditions, but I need to read your links first.
Haha, for some reason, your response made me think of this classic Dilbert: https://dilbert.com/strip/2018-05-30

Sorry, just some late night musings that writing down helped clarify in my mind. I had wondered if the JBL 1400 was also meant to be slightly listened to off-axis. It's interesting that the M2 setup manual doesn't suggest toing-in to cross in front of the listening position. On the other hand, the Gradient Helsinkis seem to have been designed to set up in such a way as you describe (https://www.stereophile.com/content/gradient-helsinki-15-loudspeaker-measurements), if I'm interpreting these words "Salmi also explained that it was not reasonable for me to make anechoic measurements at 0° because no one listens to the Helsinki from directly in front of the speaker, instead toeing in the speakers by 10–30° degrees" correctly ("toeing in" vs toeing out from directly on-axis).

I forgot to include this link, as well, for anyone who might be interested: https://secure.aes.org/forum/pubs/journal/?ID=524. I wonder if the Salon 2's increasing directivity above 6-7 kHz, especially above 10 kHz, might result in a steady-state room curve that droops similarly to the "all listeners" one.
 
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A 3-way would also potentially lower THD and IMD.

I wonder if the preference for the Ultima Salon2 over the M2 could partly have been due to the former being a 4-way.

The Ultima Salon2 is a thoroughly developed product with purposely designed drivers, each handling only a few octaves, whereas the M2 uses 2 off-the-shelf PA drivers to cover the whole range.

The 2216Nd is a nice woofer, but it's basically composed of a midrange motor structure with a subwoofer cone and suspension.
There's a lot of DSP involved in the response of the M2 (boosted low-end a.o.) and I'm not surprised people have critized the slightly muddy, less refined 500-800Hz range.

In addition, the Ultima's cabinet is clearly superior to the simple M2 cab. The generous roundovers reduce edge diffraction and thereby improve clarity (and imaging) throughout the upper mid-range and treble (hardly any secondary sources).

Like the gazillion amount of high-end tower speakers on the market (Avalon, B&W, Wilson, Gamut, Rockport, Verity, YG Acoustics etc.) the Salon2 basically consists of a mid-high section on top of a low-mid/(sub)bass cab.
I think Kevin Voecks and his team did an excellent job and it's not without reason the speaker has been available for more than 12 years. The Salon2 is one of the very few high-end speakers I seriously consider buying (I almost did some months ago when a pair was offered for €4800).
 
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