Electrostatic speakers?

[Mr. Widget]

It's not that hard to set up ESLs for near field listening...

View attachment 549819

Who needs electrostatic headphones?

 

[mps]

Who needs electrostatic headphones?

Indeed, I often describe my ESL57s as giant headphones due to the small sweet spot . However, I’ve always wondered at how good they continue to sound outside the sweet spot even with the obvious loss of high frequencies.

 

[MattHooper]

However, there's also another benefit with a speaker and the use of large planar driver that I find is often overlooked. And that is the minimization of vertical reflections due to a narrow dispersion. Contrary to Toole's research I have found in various AB tests that this matters a lot. Especially with various music material and recording of less quality. Besides a better imaging and insight into the recorded material the result is smoother sound, less harshness, and much less listening fatigue over time.

I’m in no position to validate such ideas.

But just anecdotally… the acoustician and architect who were involved in renovating my listening room created a ceiling build-down or bulkhead - a large set of metal framework covered by stretched brown felt behind which acoustic material was strategically placed.

I also have the whole floor covered by wall to wall, thick pile shag rug.

The sound of loudspeakers in this room has been exceedingly smooth and free of any harshness, brightness, grain, grit, or fatiguing qualities. It’s like you can just keep turning the sound up and up with total relaxed, comfort. Maybe that’s one of the contribution of the ceiling design:

My problem with limited dispersion speakers, whether vertical or horizontal is that I’m really not a fan of “head in vice” listening. I prefer a speaker that doesn’t change presentation obviously whether I’ve moved some up below or above or off to the sides. Even when I just I’m listening and I get up from the seat, if I hear a substantial change in tonality or a weird shifting it just annoys me.

So most of the loudspeakers like the ones I currently own have nice performance horizontally and vertically. Perhaps with the acoustic treatments in the room I’m able to get the best of both worlds for my purposes - the type of dispersion I like that keeps an even tonality over a wider area while at the same time mitigating unwanted reflections.

I don’t know, but that’s what it sounds like to me.

What I don't like about electostatics is the lack of dynamics and "punch". And the use of subwoofer doesn't close that gap 100% because there's a a need for better dynamics higher in frequency as well.

Exactly my impressions of every electrostatic speaker, including hybrid, I’ve ever heard. Again, with caveats, through informal listening.

It’s the reason I moved on from electrostatic speakers. I basically got back into high-end audio in the 90s having become enamoured of the sound I heard from my friends Quad ESL 63s. I bought a pair of my own Quad 63s and later added the gradient dipole subwoofers that were made for those quads. It’s still some of the best sound I think I’ve ever had in my room in many ways, but after a while, there was something I couldn’t help notice.
I had a pair of modest sized Thiel model 02 speakers that my wife had owned. They were just a 2 way dynamic speaker, sold quite cheaply by Thiel before they got into the whole time/phase coherence designs.

Occasionally, I would hook those speakers up to my system and every time I did, I found myself thinking “ why I am I enjoying this presentation so much? Why do I seem to be connecting even more with the music?”

Even though those Thiel bookshelf speakers only went down to 45 Hz at best, and the QUAD/Gradient system went lower, voices and instruments through the entire frequency range on the Thiels just seemed to be more powerful, more dense, more palpable, with a greater sense of the instruments moving air in the room.

So I had this:

Compared to these in the same room:

And the little guys just sounded more ballsy and dynamic to me.

When I would switch over to the dipole quad set up, I got more of an impression of hearing finally detailed renderings of the instruments… but more like I was peering through a window into music taking place in another room. It just didn’t seem to activate the room I was in so much.

Once I noticed this, I couldn’t unnoticed it.

Eventually moved onto dynamic speakers and never looked back. Even though I still love electrostatics as a place to visit.

 

[Floyd Toole]

All this talk about speaker directivity and room reflections. How about the boundary conditions of the listener? I don't see anything to attenuate strong early reflections from the window wall. A motorized absorbing panel?

 

[Bjorn]

I’m in no position to validate such ideas.

But just anecdotally… the acoustician and architect who were involved in renovating my listening room created a ceiling build-down or bulkhead - a large set of metal framework covered by stretched brown felt behind which acoustic material was strategically placed.

I also have the whole floor covered by wall to wall, thick pile shag rug.

The sound of loudspeakers in this room has been exceedingly smooth and free of any harshness, brightness, grain, grit, or fatiguing qualities. It’s like you can just keep turning the sound up and up with total relaxed, comfort. Maybe that’s one of the contribution of the ceiling design:

View attachment 549831

My problem with limited dispersion speakers, whether vertical or horizontal is that I’m really not a fan of “head in vice” listening. I prefer a speaker that doesn’t change presentation obviously whether I’ve moved some up below or above or off to the sides. Even when I just I’m listening and I get up from the seat, if I hear a substantial change in tonality or a weird shifting it just annoys me.

So most of the loudspeakers like the ones I currently own have nice performance horizontally and vertically. Perhaps with the acoustic treatments in the room I’m able to get the best of both worlds for my purposes - the type of dispersion I like that keeps an even tonality over a wider area while at the same time mitigating unwanted reflections.

I don’t know, but that’s what it sounds like to me.



Exactly my impressions of every electrostatic speaker, including hybrid, I’ve ever heard. Again, with caveats, through informal listening.

It’s the reason I moved on from electrostatic speakers. I basically got back into high-end audio in the 90s having become enamoured of the sound I heard from my friends Quad ESL 63s. I bought a pair of my own Quad 63s and later added the gradient dipole subwoofers that were made for those quads. It’s still some of the best sound I think I’ve ever had in my room in many ways, but after a while, there was something I couldn’t help notice.
I had a pair of modest sized Thiel model 02 speakers that my wife had owned. They were just a 2 way dynamic speaker, sold quite cheaply by Thiel before they got into the whole time/phase coherence designs.

Occasionally, I would hook those speakers up to my system and every time I did, I found myself thinking “ why I am I enjoying this presentation so much? Why do I seem to be connecting even more with the music?”

Even though those Thiel bookshelf speakers only went down to 45 Hz at best, and the QUAD/Gradient system went lower, voices and instruments through the entire frequency range on the Thiels just seemed to be more powerful, more dense, more palpable, with a greater sense of the instruments moving air in the room.

So I had this:

View attachment 549833

Compared to these in the same room:

View attachment 549834

And the little guys just sounded more ballsy and dynamic to me.

When I would switch over to the dipole quad set up, I got more of an impression of hearing finally detailed renderings of the instruments… but more like I was peering through a window into music taking place in another room. It just didn’t seem to activate the room I was in so much.

Once I noticed this, I couldn’t unnoticed it.

Eventually moved onto dynamic speakers and never looked back. Even though I still love electrostatics as a place to visit.

If that ceiling absorbent has been used with something that's works well at least down to the Schoeder frequency it combines a very elegant solution with great effect. Looks really nice. Every considered a glass diffuser to place in front of the window? Or something movable?

Your point about limited dispersion makes of course a lot of sense if you care about how it listens when you're standing. Personally I don't see that as limitated in my dedicated listening room where I only sit, but for another living room when it's also used for backround listening I use a speaker with a bit wider vertical dispersion but still limited to minimize floor and ceiling reflections (a horn speaker).

I think one of the most important aspect in listening to audio is the avoidance of harshness, brightness, grit, etc. Crucial in order to enjoy various music material and avoid listening fatigue. Attenuating strong early reflections is important in that regard IMO and that something electrostatics do incredible well.

 

[MattHooper]

If that ceiling absorbent has been used with something that's works well at least down to the Schoeder frequency it combines a very elegant solution with great effect. Looks really nice.

Thanks. Yes there are some really big long thick areas stuffed with Rockwool (IIRC) especially at room boundaries. That’s not only the case in parts of the ceiling, but also hidden in parts along the screen wall with large portions of thick Rockwool in the room corners behind the speakers as well.
I don’t remember the measurements, but I sure seem to get great sound with most loudspeakers I put in the room.

Every considered a glass diffuser to place in front of the window? Or something movable?

I find no need. The room ended up I think as something close to a live end-dead end, with the dead end being the front wall behind the loudspeakers, and the more live and being around the listening position.
Which I also modulate with curtains for wall reflections.

There’s nothing at all about the sound that is suggesting any obvious issues to me from reflections behind the listening seat (my head ends up about 4 1/2 feet from the windows behind). Tonality is bang on perfect to my ears, imaging and sound staging bang on.
“No notes” . So I wouldn’t find any need to introduce something more cumbersome or possibly aesthetically offputting. Also, there happens to be a projector hidden behind the listening sofa. So that would get in the way of what you might be suggesting anyway.

I do have curtains that I can pull all the way across the back wall behind me, but I find when I do that room sounds too dead and I don’t like the results.

 

[mrehorst]

I find no need. Room end up I think is something close to a live and dead end, with the dead end being the front wall behind the loudspeakers, and the more live and being around the listening position.

I do have curtains that I can pull all the way across the back wall behind me, but I find when I do that room sounds too dead and I don’t like the results.

I have a similar setup with a diffuse front wall treatment and large windows behind the listening position. There are heavy velvet curtains that I can close over the windows but I find the room too dead with the curtains closed. When the curtains are open I too have approximately live-end/dead-end set up and it sounds great. One of these days I'll try to make reverberation measurements with the curtains open and closed to see what is actually happening.

The room is L shaped, and I get a strong reflection off the wall with the plants (left side), but no real reflection (or at least a much delayed one) on the right side which screws up the imaging a bit with some music.

 

[MarkS]

the bass response in the room cannot be solved by a stereo pair of loudspeakers

Not even with DSP, and for a single listening position, and assuming enough positional flexibility to keep that listening position out of deep nulls?

 

[MattHooper]

All this talk about speaker directivity and room reflections. How about the boundary conditions of the listener? I don't see anything to attenuate strong early reflections from the window wall. A motorized absorbing panel?
View attachment 549835

Hi Floyd,

I presume you are referencing my post and the photos of my listening room (?).

If so, I’m certainly not presenting it as a perfect listening room. We did the best we could with the old circa 1830s living room I had to work with. And the fact I also wanted it to perform separate duty as a high performance projection based home theatre as well as house a separate two channel system only added to the complexity.

As I mentioned to Bjorn I haven’t felt any need to do anything about the bay windows behind my listening sofa. My head ends up about 4 1/2 feet from the windows FWIW.

The room is sort of live end dead end with the more dead end being the screen wall behind my loud speakers - it’s largely covered in black velvet, and the screenwall and areas around it are filled with Rockwool in strategic places, including large thick columns hidden out of sight in the room corners behind the speakers, and also at the top of the ceiling/wall corner:

I also have thick curtains I can pull to any points along the side walls to attenuate some of the upper frequencies.

Subjectively, I find the sound to be beautifully balanced… and for instance, when a sound slowly pans from one loudspeaker across the sound stage to the other speaker, the tone and timber remains very consistent.

And, having dialled things into my taste, the soundstaging and imaging is among the best I’ve heard.

So I just have no complaints to address with regard to whatever might be happening from the bay windows. (I do have curtains I can pull across the back wall covering those windows, but then the room starts to sound a bit too dead and I don’t like that effect).

So it is what it is.

I actually incorporated dual subwoofers and room correction at one point to augment my floor standing speakers and even out the bass as much as possible, but even after living with it for a while I ultimately preferred the sound of the speakers without the subwoofers and room correction.
Whatever bass coloration is not highly evident to me - the bass sounds very smooth and I preferred the overall tone and punch without the subwoofers/room correction. I guess that’s possibly the result of just getting used to the way speakers sound in this room.

Of course, if you weren’t referring to my post or photos… to quote the great Emily Litella…”Never mind…”.

 

[MattHooper]

I have a similar setup with a diffuse front wall treatment and large windows behind the listening position. There are heavy velvet curtains that I can close over the windows but I find the room too dead with the curtains closed. When the curtains are open I too have approximately live-end/dead-end set up and it sounds great. One of these days I'll try to make reverberation measurements with the curtains open and closed to see what is actually happening.

View attachment 549837
The room is L shaped, and I get a strong reflection off the wall with the plants (left side), but no real reflection (or at least a much delayed one) on the right side which screws up the imaging a bit with some music.

Quad 63 sighting! Awesome.

Looks great.

Sometimes I admit, I miss my quads. Would’ve been nice to keep them to revisit that sound sometimes. I liked them better than any Martin Logan I’ve heard.

 

[goryu]

I'm very happy with my Acoustat Spectra 6600's and 4 subs. Had the bias supplies and the main boards replaced with new updated boards made by a fellow in Iowa who does Acoustat repairs and upgrades. He's the head tech on a radio telescope and has been taking these speakers to a new level. Mike Burgert is his name and he's a regular contributor on the Acoustat Facebook group page.

 

[Bjorn]

Thanks. Yes there are some really big long thick areas stuffed with Rockwool (IIRC) especially at room boundaries. That’s not only the case in parts of the ceiling, but also hidden in parts along the screen wall with large portions of thick Rockwool in the room corners behind the speakers as well.
I don’t remember the measurements, but I sure seem to get great sound with most loudspeakers I put in the room.




I find no need. The room ended up I think as something close to a live end-dead end, with the dead end being the front wall behind the loudspeakers, and the more live and being around the listening position.
Which I also modulate with curtains for wall reflections.

There’s nothing at all about the sound that is suggesting any obvious issues to me from reflections behind the listening seat (my head ends up about 4 1/2 feet from the windows behind). Tonality is bang on perfect to my ears, imaging and sound staging bang on.
“No notes” . So I wouldn’t find any need to introduce something more cumbersome or possibly aesthetically offputting. Also, there happens to be a projector hidden behind the listening sofa. So that would get in the way of what you might be suggesting anyway.

I do have curtains that I can pull all the way across the back wall behind me, but I find when I do that room sounds too dead and I don’t like the results.

There's nothing better than to hide acoustic treatment that way and have it look like an ordinary living room. Very clever.

Just a side note. Curtain, and even thick ones, are very band limited. Only absorbing in the very highest frequencies and therefore unevenly. That leads to what exactly what you mention - sounding too dead. Your carpet only contributes some in that area. While a thick carpet is more bradband than a curtain, it's still quite bandlimited and doesn't absorb as low as what's ideal.
But clearly there's nothing to change if you're happy with the result.

While you not strictly speaking of a LEDE room, it may be of interest to know that a live end-dead end design and which was only used for a short period of time in studio design required a room with very good distance to the rear wall. The contribution from the rear wall mostly arrived around 20 ms after the direct sound. But this design quickly changed to the use of diffusion as soon as they were introduced. And with discovery of ETC measurement, the dead front part changed from all absorptive to sparce and surgically treatment of reflected energy. Thus a LEDE room eventually looked more like the below with late arrival diffuse energy to resemble spaciousness and envelopment of concert halls.

And of course; with the use of slanted walls instead of absorpion it gave further increased diffused energy with an even more live result and added spaciousness. Extremely addictive to listen to! Far more correct and accurate than what's achieved with multiple speakers.

 

[Bjorn]

I have a similar setup with a diffuse front wall treatment and large windows behind the listening position. There are heavy velvet curtains that I can close over the windows but I find the room too dead with the curtains closed. When the curtains are open I too have approximately live-end/dead-end set up and it sounds great. One of these days I'll try to make reverberation measurements with the curtains open and closed to see what is actually happening.

View attachment 549837
The room is L shaped, and I get a strong reflection off the wall with the plants (left side), but no real reflection (or at least a much delayed one) on the right side which screws up the imaging a bit with some music.

A reverberation measurement is meaningless in a small room because there's is no diffuse field, something that is required to have reverberation. Instead you have specular energy or high gain reflections. The fact that you have high gain reflections from the rear wall/window is actually a proof that reverberation does not exist.

 

[Bjorn]

I'm very happy with my Acoustat Spectra 6600's and 4 subs. Had the bias supplies and the main boards replaced with new updated boards made by a fellow in Iowa who does Acoustat repairs and upgrades. He's the head tech on a radio telescope and has been taking these speakers to a new level. Mike Burgert is his name and he's a regular contributor on the Acoustat Facebook group page.

I can imagine that sounds great. And you overcome a lot of the dynamic drawbacks with the use of 4 subwoofers.

 

[Marc v E]

Because the circumstances under which they listen introduce several opportunities for biasing factors having nothing to do with the sound. Listening blind is an obvious starting point. Many others are described in detail in my books, and in my first JAES paper 44 years ago - the title says it all: Toole, F. E. (1982). “Listening tests – turning opinion into fact”, J. Audio Eng. Soc., 30, pp. 431-445. Much has been learned since, but it was a solid start.

The fact is that among other things human adapt to - normalize - many very significant flaws, not recognizing them until something better is heard in comparison. Most of us have enjoyed music through inferior sound systems at some points in our lives.

Given that people adapt to an incorrect speaker and that obviously costs effort, is it common that people feel less tired after switching to a neutral sounding speaker? I've seen lots of comments and accounts suggesting this. But I'm curious what your experience has been during tests.

 

[Floyd Toole]

There's nothing better than to hide acoustic treatment that way and have it look like an ordinary living room. Very clever.

Just a side note. Curtain, and even thick ones, are very band limited. Only absorbing in the very highest frequencies and therefore unevenly. That leads to what exactly what you mention - sounding too dead. Your carpet only contributes some in that area. While a thick carpet is more bradband than a curtain, it's still quite bandlimited and doesn't absorb as low as what's ideal.
But clearly there's nothing to change if you're happy with the result.

While you not strictly speaking of a LEDE room, it may be of interest to know that a live end-dead end design and which was only used for a short period of time in studio design required a room with very good distance to the rear wall. The contribution from the rear wall mostly arrived around 20 ms after the direct sound. But this design quickly changed to the use of diffusion as soon as they were introduced. And with discovery of ETC measurement, the dead front part changed from all absorptive to sparce and surgically treatment of reflected energy. Thus a LEDE room eventually looked more like the below with late arrival diffuse energy to resemble spaciousness and envelopment of concert halls.

View attachment 549877

And of course; with the use of slanted walls instead of absorpion it gave further increased diffused energy with an even more live result and added spaciousness. Extremely addictive to listen to! Far more correct and accurate than what's achieved with multiple speakers.

View attachment 549878

This triggered another memory. Back in the days of LEDE (live-end-dead-end) control rooms I was invited to visit a new control room designed using the principles. The new facility had just been completed and the movers were still in the building. It looked much like the Tele-Image room shown in your post - lots of beautiful, expensive, wood RPG diffusers across the back wall. When I bellied up the the center of the console and listened to some demo tapes I thought I heard some strangeness.

So, I asked for mono pink noise to be delivered through the L & R loudspeakers. Instead of a solid center image what I heard was a sound blur distributed over much of the soundstage - there was no convincing center image. I invited the recording engineers in attendance to try it, and they agreed, and were quite upset. What was going on?

My knowledge of binaural hearing told me that the ears were receiving too much decorrelated sound from a direction that did not allow the hearing system to discriminate against it. Put into plain English, the sense of space that we enjoy in concert halls and surround sound is created by reflected sounds arriving from the sides. In this control room the strong reflected sounds were coming from the rear, covering the same mirror-image angle as the front soundstage. These sounds simply add confusion to the intended soundstage cues from the front.

I asked someone to find the movers and get a few moving blankets. We hung them over the central portion of the rear diffusers and repeated the listening test - the center image was compact and solid, as it should be. There now was a full stereo soundstage. As I expressed it at the time: a $5 solution for a $20k problem. So it is not that rear wall diffusion is bad, but that in this case it was excessive. Some side wall reflection would likely have been a welcomed addition. However, now it seems that direct-sound dominance is the fashion with near-field listening and acoustically dead, reflection-controlled rooms often employed. These are far from the listening conditions of normal consumers., but part of these elaborate "designed" control rooms is their appearance. There is a marketing aspect. Sadly some consumers think that they represent desirable designs to imitate because they are "professional". The 4th edition of my book has something to say about this and how it affects the "translation" of recorded arts from control and mastering rooms to homes. The fact that many widely used monitor loudspeakers of the LEDE period had atrocious off-axis sound performance was good reason to absorb early reflections to improve sound quality. I show some measurements in the book. But loudspeakers have improved and room acoustics need to follow.

I am positive that the ETC measurements in this control room were impressive, but omnidirectional microphones are not the equivalent of two ears and a brain. This kind of acoustical design lacked fundamental understanding of human hearing. Science was invoked but it was misapplied science. I did not pursue the obvious matter of how that control room could have progressed to that final stage and no engineer noticed that the stereo soundstage was seriously compromised. Humans adapt, even professional recording engineers.

In the little diagram I showed in an earlier post, with the rear wall reflections in a listening room is an extreme example of strong rear-wall reflections. To restore precise stereo imaging it is not necessary to cover entire walls with absorbers, just a small portion behind the listener's head. The acoustical performance of the room is unchanged. Even a cushion has been shown to be enough to make an easily audible improvement when the head is close to a reflective rear wall. Let the dominant soundstage cues arrive from the front and sides.

 

[Floyd Toole]

is it common that people feel less tired after switching to a neutral sounding speaker?

I can only speak for myself, and the answer is yes. I have experienced a great many loudspeaker comparisons and I do feel something like a sense of relief when a more neutral loudspeaker is heard. How this translates into long term feelings of "fatigue" I honestly cannot comment on. I have always had loudspeakers that were at or close to the state-of-the-art and lately multi-sub bass correction schemes. They have been extremely gratifying to live with. I don't like all that I hear, but I know where the problems originate - not in my room.

EDIT: as I was writing this I had been listening to my wife's favorite light classical streaming station. She left and I switched to my version, one that has less compression and who knows what other processing. The music is the same but the sound is such that I immediately felt a weight being lifted off me. It is simply more natural, more relaxing. The basic "sound quality" has not changed noticeably but the experience has. Is it real or am I experiencing a personal bias?

 

[Bjorn]

This triggered another memory. Back in the days of LEDE (live-end-dead-end) control rooms I was invited to visit a new control room designed using the principles. The new facility had just been completed and the movers were still in the building. It looked much like the Tele-Image room shown in your post - lots of beautiful, expensive, wood RPG diffusers across the back wall. When I bellied up the the center of the console and listened to some demo tapes I thought I heard some strangeness.

So, I asked for mono pink noise to be delivered through the L & R loudspeakers. Instead of a solid center image what I heard was a sound blur distributed over much of the soundstage - there was no convincing center image. I invited the recording engineers in attendance to try it, and they agreed, and were quite upset. What was going on?

My knowledge of binaural hearing told me that the ears were receiving too much decorrelated sound from a direction that did not allow the hearing system to discriminate against it. Put into plain English, the sense of space that we enjoy in concert halls and surround sound is created by reflected sounds arriving from the sides. In this control room the strong reflected sounds were coming from the rear, covering the same mirror-image angle as the front soundstage. These sounds simply add confusion to the intended soundstage cues from the front.

I asked someone to find the movers and get a few moving blankets. We hung them over the central portion of the rear diffusers and repeated the listening test - the center image was compact and solid, as it should be. There now was a full stereo soundstage. As I expressed it at the time: a $5 solution for a $20k problem. So it is not that rear wall diffusion is bad, but that in this case it was excessive. Some side wall reflection would likely have been a welcomed addition. However, now it seems that direct-sound dominance is the fashion with near-field listening and acoustically dead, reflection-controlled rooms often employed. These are far from the listening conditions of normal consumers., but part of these elaborate "designed" control rooms is their appearance. There is a marketing aspect. Sadly some consumers think that they represent desirable designs to imitate because they are "professional". The 4th edition of my book has something to say about this and how it affects the "translation" of recorded arts from control and mastering rooms to homes. The fact that many widely used monitor loudspeakers of the LEDE period had atrocious off-axis sound performance was good reason to absorb early reflections to improve sound quality. I show some measurements in the book. But loudspeakers have improved and room acoustics need to follow.

I am positive that the ETC measurements in this control room were impressive, but omnidirectional microphones are not the equivalent of two ears and a brain. This kind of acoustical design lacked fundamental understanding of human hearing. Science was invoked but it was misapplied science. I did not pursue the obvious matter of how that control room could have progressed to that final stage and no engineer noticed that the stereo soundstage was seriously compromised. Humans adapt, even professional recording engineers.

In the little diagram I showed in an earlier post, with the rear wall reflections in a listening room is an extreme example of strong rear-wall reflections. To restore precise stereo imaging it is not necessary to cover entire walls with absorbers, just a small portion behind the listener's head. The acoustical performance of the room is unchanged. Even a cushion has been shown to be enough to make an easily audible improvement when the head is close to a reflective rear wall. Let the dominant soundstage cues arrive from the front and sides.

I suspect you have either heard poor diffusers, diffusers that were placed too close to the listening position or a combination of these two.

If multiple diffusers are used, one needs to follow the barker sequency to avoid periodicty and lobing. In a control room they should be placed so they the diffused energy arrives 2-5 ms after the intial time delay of the recording room. And certainly not be used if the distance to the rear wall is short.

Correct use of diffusion of high quality doesn't sound like you describe. I have yet to hear anyone prefer absorption over diffusion in the rear of the room with sufficient distance. They are still used a lot in control rooms. Today they are also improved with smaller wells that function higher in frequency and with a diffuser like the Modffractal, the barker code is built into the units.

Lateral diffusion is achieved with the diffusers sending energy via rear walls before it reaches the listener. Diffusion sent from corners directly to ears can also arrive in an angle that is very audible and similar to lateral energy. The width of the room isn't sufficient to support the 2-5 ms intial time daly gap for a control room, but certianly something that can be done at home.

Absorption in the rear of the room is IMO only the right treatment if distance to that wall is very close, and as you point out only a smaller area needs to be treated with it. Diffusion or hybrid (semi diffusion of higher frequencies and absorption of lower frequencies) is generally preferable with more distance. Without the added spaciousness from phase grating diffusion, stereo tends to lack the developing experience shoe size concert halls have.

 

[Duke]

I have experienced a great many loudspeaker comparisons and I do feel something like a sense of relief when a more neutral loudspeaker is heard. How this translates into long term feelings of "fatigue" I honestly cannot comment on.

Regarding "listening fatigue" this comes to mind:

You may be familiar with the phenomenon of students sitting in the rear of a large lecture hall becoming so fatigued that they have trouble simply staying awake, much less comprehending complex ideas and committing them to long-term memory. My understanding is that David Griesinger links this to the cognitive load of trying to understand speech in an overly reverberant environment. The brain has a limited amount cognitive ability available. By the time the ear/brain system has deciphered one word, the lecturer has moved on to the next word, and there neither sufficient time nor sufficient surplus cognitive ability to string many words together into complex thoughts and even more complex concepts, and then to commit those complex concepts to long-term memory. After about ten or fifteen minutes that part of the brain is so fatigued the student gets a headache and/or becomes sleepy. (Imo this is a pretty good argument for sitting up near the front whenever possible.)

Perhaps something broadly similar can happen with less neutral loudspeakers even if their sound is not distractingly colored, imposing a heightened cognitive load on the relevant portion of the ear/brain system which over time results in listening fatigue.

In the Harman blind listening tests was listening fatigue observed, and if so, did it seem to track with perceived sound quality?

 

[rcstevensonaz]

You may be familiar with the phenomenon of students sitting in the rear of a large lecture hall becoming so fatigued that they have trouble simply staying awake,

On a personal note, I am much more familiar with the phenomenon of being a student sitting in the rear of a large lecture hall because I'm so fatigued that I will have trouble simply staying awake.