The Reverberant Field: Why it matters, where the goal posts are

Duke LeJeune

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#1
All of the differences between the sound in a good room and the sound in a bad room are in the reverberant field.

All of the money spent on acoustic construction and treatment at home, in professional studios, and in concert halls is spent on the reverberant field.

Most of the sound that reaches your ears in most rooms is reverberant sound (nearfield and quasi-anechoic setups being the exceptions).

Done right in a home audio setting, the reverberant field enriches timbre, improves clarity, and enables the spatial information on the recording to come through, which (given a good recording) includes a sense of immersion in the original acoustic space (whether it be natural or synthetic or both).

Done wrong in a home audio setting, the reverberant field degrades timbre and clarity, superimposes a "small room signature" and/or a characteristic coloration onto every recording, and causes listening fatigue.

In this thread I'm going to look at the loudspeaker's role in getting the reverberant field right, and will leave acoustic treatments to those with expertise in that field.

In my next post, we'll try to get an idea of where the goal posts are by looking through the lens of one of the world's foremost experts on concert hall acoustics and psychoacoustics, Dr. David Griesinger.
 
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Duke LeJeune

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#2
Acoustician and psychoacoustician David Griesinger gave a lecture entitled "The effects of early reflections on proximity, localization, and loudness". In my opinion the most fascinating part of the lecture was a demonstration of the effects of early and late reflections on sound quality.

David processed a binuaral recording he had made at his seat in a concert hall to separate out the first-arrival sound, the early reflections, and the late reflections. In the clip below, starting at about 13:18 and going to about 15:21, David presents four audio clips.

(These clips blew my mind. Headphones or earbuds recommended.)

The first clip is the direct sound only (note that the low end is lacking because the processing includes time-gating, which doesn't allow the low frequencies through).

The second clip is the direct sound + early reflections (no late reflections).

The third clip is the direct sound + late reflections (no early reflections).

The last clip is everything: Direct sound + early reflections + late reflections.

If all goes well, the video clip will start at about 13:18; he moves on to other topics at about 15:21:


Did you notice how sweet that third clip sounded? Here, go back and listen to it one more time (starts at 14:20):


So what do we learn from this?

We learn that early reflections are detrimental while late reflections are beneficial. This is hardly a new concept, but now we didn't just read about it - we heard it. Every clip that included the early reflections had degraded clarity, but in the clip of the direct sound + late reflections only, those reflections enhanced the direct sound with no audible downside.

Imo that's where the goal posts are!

In my first post I said that the reverberant field done right "enriches timbre, improves clarity, and enables the spatial information on the recording to come through." Despite the less-than-ideal signal chain, could you hear these things happening in that third clip?

So, we want to minimize the early reflections but encourage the later ones. The time scale will be of course different in our smaller rooms, but the general principle seems to be valid (I'll explain later) [edit: see Post #25]. And we also want those reflections to be spectrally correct... more on that topic in a future post [edit: see Post #12].
 
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spiritofmusic

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#3
So, if late reflections are good, why do so many audiofools aspire to overtreat their listening rooms?

Whenever I see pics of rooms expensively treated, there are 9x6 diffuser panels on the front wall, giant bass traps, often the ceiling all way btwn seat and spkrs fully treated, and side walls way more than just first and second reflection points treated.

Those rooms w SMTs and ASCs seem to be particularly plastered w panels/traps.
 
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Duke LeJeune

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#5
So, if late reflections are good, why do so many audiofools aspire to overtreat their listening rooms?
In some cases it may be a well-intentioned mistake.

But if someone has speakers speakers whose off-axis response is not very good, and therefore results in a reverberant field which is detrimental, judicious use of absorption may make sense. However my understanding is that doing so correctly is easier said than done - the effectiveness of absorptive material goes down as the wavelengths get longer, so using only relatively inexpensive absorption rolls off the top end of the reverberant energy moreso than the rest of the spectrum. So some reflection and/or diffusion is usually deliberately included with the absorption.

In my experience diffusion seems to be generally beneficial, whether or not it is combined with absorption. But I am NOT an expert in this area!

Having been in several rooms treated by an award-winning professional, Jeff Hedback,, I have retired from armchair-quarterbacking room treatments. I spent a little time in a studio that Jeff had treated and with eyes closed the room sounded about twice as big as it was. The gap between what I can do as an enthusiastic amateur in the field, and what someone like Jeff can do (without necessarily prescribing dedicated "acoustic treatment products") is just too wide.

Speaking of Jeff, he was interviewed by Larry Borden of Dagogo several years ago: https://www.dagogo.com/an-interview-with-jeff-hedback-of-hdacoustics/
 

Folsom

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#6
Those sound bites are interesting for sure.

But his first reflection might be a little more intense than we typically experience. They are bad, but that was horrific.

Does this mean you are going to make a dipole?
 
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Duke LeJeune

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#7
Those sound bites are interesting for sure.

But his first reflection might be a little more intense than we typically experience. They are bad, but that was horrific.

Does this mean you are going to make a dipole?
Yeah the Griesinger clips are not a direct reflection of what we experience at home... bad pun intended... but I think the general principles apply, and imo dipoles offer anectodal evidence of it: Countless owners of Maggies and Martin Logans and SoundLabs and Acoustats and so forth have found a significant improvement when they pull their speakers well out into the room. In particular relatively narrow-pattern panel speakers can be positioned for minimal early reflections, and then given sufficient distance from the wall, the arrival of that additional reverberant energy from the backwave is delayed long enough that it's beneficial rather than detrimental (though usually not to the extent illustrated by that third Griesinger clip).

To answer your question, I'm not planning to do a dipole.
 

KlausR.

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#8
Hello Duke,

Yeah the Griesinger clips are not a direct reflection of what we experience at home... bad pun intended... but I think the general principles apply, ...
Small rooms and performance spaces are perceptually different. Perception thresholds of first reflections are different for short and long delays, they generally decrease with increasing delay, the reflections are hence easier to spot.

Schubert (1966), “Detectability of single reflections for music” (Untersuchungen über die Wahrnehmbarkeit von Einzelrückwürfen bei Musik), Technische Mitteilungen RFZ, vol. 10, no. 3, p.124

In the normal domestic listening room you won't find early reflections delayed by more than say 20-30 ms (equals 7-10 m travelling distance). What were the delays in the concert hall? What were the delays for late reflections?

In view of the above the conclusion is that one cannot use results of experiments in (large) performance spaces and transcribe them to (small) domestic listening rooms.

Then the recording: binaural or not, a pair of microphones is not the same as as pair of ears! The pair of ears is followed by a sophisticated CPU, the whole thing works very different when compared to a set of mikes: binaural decoloration, predence effect, perception thresholds: human hearing has them, a set of mikes does not.

Litovsky et al., “The precedence effect”, J. of the Acoustical Society of America 1999, vol. 106, no. 4, pt. 1, p.1633
Salomons (1995), “Coloration and binaural decoloration of sound due to reflections”, Thesis, Delft University


I have read all psychoacoustic research I could find re: early reflections, and so far there is no evidence that they are a problem as matter of principle.

You mention the reverberant sound field: I suppose that this is the equivalent term for diffuse sound field?

As measurements have clearly shown, diffuse fields do not exist in small rooms, the field is rather (highly) directional.

Gover et al. (2004), “Measurements of directional properties of reverberant sound fields in rooms using a spherical microphone array”, J. of the Acoustical Society of America 2004, Vol.116, No.4, Pt.1, S.2138

Merimaa et al. (2001), “Measurement, analysis and visualisation of directional room responses”, Audio Engineering Society preprint 5449 (2001)

Meyer (1954), „Definition and diffusion in rooms“, J. of the Acoustical Society of America 1954, Vol.26, No.5, S.630

I attach my write-up on early reflections.

Klaus
 

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DaveC

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#9
I think we also need to consider Toole's views that spectrally correct early-arriving 1st reflections seem to be preferred in their testing. Kieth Johnson of Reference Recordings also holds this view, I was lucky enough to ask him some questions at a Avalon demo...

Not saying I agree, but why would some/most people prefer this?

IMO there are some issues with Harman's testing, but aside from that I think listener acclimation is a major issue, especially for those who don't have a lot of experience listening to music from different systems and don't listen to live music... 99.9% of what they hear may come from one system with characteristics they become acclimated to. I hate to say it, but not everyone's opinion is well qualified.

Also, how about differences between speakers designed for dedicated rooms vs typical living rooms? I think looking at this issue is also part of the answer to the preference for 1st reflections. IME a dedicated room can make a wide dispersion speaker work well, and conversely it may not be optimal for a typical living room, with a lot being left to chance.
 
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Duke LeJeune

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#10
Small rooms and performance spaces are perceptually different. Perception thresholds of first reflections are different for short and long delays, they generally decrease with increasing delay, the reflections are hence easier to spot...

... one cannot use results of experiments in (large) performance spaces and transcribe them to (small) domestic listening rooms.
Thank you very much for taking the time to write such an in-depth reply, Klaus. I respect your opinions and the professional level of scholarship you bring.

I agree that perception thresholds for first reflections are different for different delay times, but imo that does not change this basic principle articulated by David Griesinger:

“The earlier a reflection arrives the more it contributes to masking the direct sound.”

I take David's recordings as illustrative of this general principle, rather than as being limited in applicability to large rooms only. While I wouldn't “transcribe” the results of experiments in large rooms to small rooms, in this case I certainly would not dismiss them (not saying that you are dismissing them, just advocating for a middle ground).

In the normal domestic listening room you won't find early reflections delayed by more than say 20-30 ms (equals 7-10 m travelling distance). What were the delays in the concert hall? What were the delays for late reflections?
I don't know what the delays were, but clearly far greater than in a home audio setting.

I have read all psychoacoustic research I could find re: early reflections, and so far there is no evidence that they are a problem as matter of principle.
In the spirit of "a picture is worth a thousand words", I re-submit the sound clips from that Griesinger lecture, post #2 above. If those clips are not evidence of early reflections being detrimental, I don't know what is. (In the last clip [direct + early + late] the clarity seems better than in the second clip [direct + early], and I assume backwards masking is playing a role in that.)

I think Geddes would also disagree with your position. He suggests a target of avoiding reflections arriving within 10 milliseconds of the direct sound. In his room he breaks up the floor and ceiling reflections, as their path lengths are inevitably too short for his 10 ms target.

I agree with Geddes based on my own experiences... not that I'm putting forward my own experiences as "primary evidence”, but rather as my “excuse” for agreeing with him.

Another way that early reflections are detrimental in home audio is, they tell you that you're in a small room. From your paper:

" The delay time of the early reflections determines the impression of the size of the room, for natural hearing and also for two-channel sound transmission (Kuhl 1978).”

Once again we have the TIME DELAY between the direct sound and the early reflections playing a role, and I think it is valid to assume that their INTENSITY plays a role as well, because detection thresholds are implicit. Therefore...

* The earlier a reflection arrives the more it contributes to masking the direct sound;

* The earlier a reflection arrives the more it contributes to "small room signature"; and

* The more intense these reflections are, the greater these effects.

It is also my understanding that early reflections are generally more likely to cause coloration than are later reflections, but I don't have a source for that handy. The direction from which a reflection arrives also plays a role, with "from the same direction as the speakers" being the least desirable, according to Toole if I recall correctly.

You mention the reverberant sound field: I suppose that this is the equivalent term for diffuse sound field?

As measurements have clearly shown, diffuse fields do not exist in small rooms, the field is rather (highly) directional.
I use the term “reverberant field” to mean “all of the reflections in the room”. I don't claim that it's a diffuse field, as in most home listening rooms I think it decays too quickly to become effectively diffuse.

Can you tell me what you mean by "the field is rather (highly) directional"? I have a vague idea of what that means but you probably have a very clear one.

I attach my write-up on early reflections.
Thank you very much, I am slowly making my way through it as time permits.
 
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Duke LeJeune

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#11
I attach my write-up on early reflections.
You paper is a gold-mine of information! Thank you again for attaching it.

I'm confused by what seems (to me) to be conflicting statements about Inter-Aural Cross Correlation (IACC). First, here are three consistent statements from page 19:

“Reflections have a positive contribution to listener preferences. The greater the difference in sounds at the two ears, the greater the sense of spaciousness (Toole 2006).”

“A high interaural cross-correlation is equivalent to high binaural similarity which results in low subjective preference (Schroeder 1979). Conversely, for more dissimilar ear signals (high binaural dissimilarity) the preference is high. Acoustic asymmetry lowers interaural cross-correlation which results in an increased sense of spaciousness and generally in increased preference.”

“Interaural cross-correlation decreases (with subsequent improved spatial impression) when the reverberation time of the room increases (Kurozumi 1983).”

So if I understand these three statements correctly, you are saying that LOW inter-aural cross-correlation is desirable. If so, then I agree.

Now, from page 20:

“Acoustic treatment results in a substantial, frequency dependent change of the interaural cross-correlation coefficient ICCC (Tohyama 1989) and results generally in a decrease of the coefficient when absorbers or diffusers are added (King et al. 2011) with subsequent narrower image (Kishinaga 1979) and leads in the extreme case of the anechoic chamber to the perceived sound field differing greatly from the original field (Tohyama 1989). “

Is ICCC the same thing as IACC?

I assume that the “perceived sound field differing greatly from the original field” is undesirable (and is a fascinating aspect of anechoic listening which I was unaware of). So this paragraph is apparently saying that a DECREASE in the IACC is UNDESIRABLE, seemingly the opposite of the preceding Page 18 quotes. I am I understanding correctly?

(Wouldn't removing all reflections INCREASE the inter-aural cross correlation, which IS undesirable?)

In your Conclusions, you wrote:

“Adding acoustic treatment (absorbers, diffusers) to first reflection points results in a decrease of the interaural cross-correlation coefficient IACC, whereas high values of IACC are preferred.”

I probably either missed something or am having a reading comprehension mis-cue, but can you help me out? Why are high values of IACC preferred on Page 19 and in your Conclusions, while low IACC was desirable back on Page 18?
 
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Duke LeJeune

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#12
I think we also need to consider Toole's views that spectrally correct early-arriving 1st reflections seem to be preferred in their testing. Kieth Johnson of Reference Recordings also holds this view, I was lucky enough to ask him some questions at a Avalon demo...

Not saying I agree, but why would some/most people prefer this?
Excellent question!!

When there is a significant spectral mis-match between the direct sound and subsequent reflections, three negative things can happen:

1. The "precedence effect" relies on the spectral content of reflections being a good match to the spectral content of the corresponding direct sound. So when there's a mis-match the precedence effect is not as... um... effective, and imaging precision can be degraded.

2. The perceived tonal balance is a weighted average of the direct + reverberant sound, so the tonal balance can be skewed by spectrally-incorrect the reflections.

3. My understanding is that listening fatigue can arise when the ear/brain system literally has to work harder to correctly match spectrally-incorrect reflections with their corresponding direct sound. Over time that part of the brain can literally become fatigued.
 

DaveC

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#13
@KlausR. and @Duke LeJeune I'd be interested on your opinions on the new Polk speakers that cancel the output of the opposite speaker in it's half of the room...

It accomplishes something similar to adding a divider in the room going from the LP to between the speakers.

What I've noticed is folks used to reflective rooms tend to describe the result of too much direct vs reflected sound, or the Polk sound, as close to headphones and initially it's met with some resistance but over a short period of time most acclimate and "get" the whole point and their brain has a chance to process the different presentation.

On the Polk speakers, one advantage is the distance in between the speakers doesn't matter as much, and it'll produce a soundstage dictated by the recording with images well outside the boundaries of the speaker in a way only the best setup and performing systems can. Of course the downside is symmetry and sitting right in the sweetspot is more important, but I wouldn't say it's like listening to a system that really beams and is head in a vice, it's more forgving than that but maybe less than an average system.

 
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DaveC

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Excellent question!!

When there is a significant spectral mis-match between the direct sound and subsequent reflections, three negative things can happen:

1. The "precedence effect" relies on the spectral content of reflections being a good match to the spectral content of the corresponding direct sound. So when there's a mis-match the precedence effect is not as... um... effective, and imaging precision can be degraded.

2. The perceived tonal balance is a weighted average of the direct + reverberant sound, so the tonal balance can be skewed by spectrally-incorrect the reflections.

3. My understanding is that listening fatigue can arise when the ear/brain system literally has to work harder to correctly match spectrally-incorrect reflections with their corresponding direct sound. Over time that part of the brain can literally become fatigued.

Sure, I get that... it's the preference for reflections that ARE spectrally correct I'm questioning. Why? Because not everyone has that preference and I think the reasons why some do and some don't are important to understand. This is where acclimation comes in and how that's accounted for. IMO that's the main issue with current understanding of preference as assumed by Toole and Keith, I don't deny the results but I think if acclimation isn't accounted for it's confounding the results.

In my own testing I've found people acclimate slowly over time to new presentations... and may come to prefer something new over what they are used to given enough experience.

An example... we all know the folks who go to audio shows and swear up and down their $3k system is just as good or better than the 6-figure systems being shown. :)

In any case, the most important driver of preference is the sense of immersion. IMO it's as simple as that. Folks key in on certain things, but they all mention the 3-D, immersive experience as a primary driver of preference. You know what NOBODY has ever commented on? Frequency response. I know where my speaker makes some compromises in this area and nobody has ever mentioned it, even extremely experienced listeners.
 
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Duke LeJeune

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#15
Also, how about differences between speakers designed for dedicated rooms vs typical living rooms? I think looking at this issue is also part of the answer to the preference for 1st reflections. IME a dedicated room can make a wide dispersion speaker work well, and conversely it may not be optimal for a typical living room, with a lot being left to chance.
You may well be correct. In my experience wide-pattern speakers benefit more from a professionally-treated room than narrow-pattern speakers do. I design for the typically atypical real-world rooms most people have to live with.

That being said, when I have worked with Jeff Hedback on a custom design for a recording studio, he has suggested radiation pattern widths that avoid strong early sidewall reflections.

This is just speculation on my part - I haven't dug deeply enough to yet call it an "opinion" - but perhaps one reason why good wide-pattern speakers are sometimes preferred over good narrow-pattern speakers is that the increased energy in the (imo undesirable) early reflections lives on to become increased energy in the (imo desirable) late reflections, and the net result is beneficial.
 
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Duke LeJeune

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#16
@KlausR. and @Duke LeJeune I'd be interested on your opinions on the new Polk speakers that cancel the output of the opposite speaker in it's half of the room...
I have no doubt that it works as advertised. The original Stereo Dimensional Array of yesteryear did, despite the outside array not having its own dedicated tweeter.

My personal preference is for speakers that multiple people can enjoy over a wide listening area, but I'd be the last person on this forum to throw stones at a designer for using multiple arrays of drivers to accomplish their goals!
 
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Duke LeJeune

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#17
it's the preference for reflections that ARE spectrally correct I'm questioning. Why? Because not everyone has that preference and I think the reasons why some do and some don't are important to understand. This is where acclimation comes in and how that's accounted for. IMO that's the main issue with current understanding of preference as assumed by Toole and Keith...
I guess I don't really have an answer. You've thought this through better than I have.

Live unamplified voices and instruments produce spectrally correct reflections, and when in doubt I try err in that direction.

In any case, the most important driver of preference is the sense of immersion. IMO it's as simple as that. Folks key in on certain things, but they all mention the 3-D, immersive experience as a primary driver of preference.
I wholeheartedly agree!

David Griesinger uses the term "envelopment", and I think he's talking about the same thing:

"Envelopment is the holy grail of concert hall design. When reproducing sound in small spaces [home listening rooms], envelopment is often absent."

"Envelopment is perceived when the ear and brain can detect TWO separate streams: A foreground stream of direct sound, and a background stream of reverberation. Both streams must be present if sound is perceived as enveloping."

Imo that second quote implies a time gap in between the foreground stream of direct sound and its corresponding background stream of reverberation is desirable, so that the ear can perceive them as SEPARATE. Imo this is dramatically illustrated by the clips he plays in the video in Post #2.

I know nothing about your speakers nor how they are set up. Do you see any correlation between your speakers and setup, and what Griesinger says about envelopment being "perceived when the ear and brain detect TWO separate streams"?
 

DaveC

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#18
I guess I don't really have an answer. You've thought this through better than I have.

Live unamplified voices and instruments produce spectrally correct reflections, and when in doubt I try err in that direction.

I'll try again on this one, lol... The options here are spectrally correct 1st reflections being present vs a speaker with directionality that avoids 1st reflections.

I agree reflections that are not correct are not desirable and I didn't mean to include them in the discussion AT ALL. :)


My speaker is a wideband driver in a ~300 Hz LeCleach Horn, a Fostex T500A super tweeter (that's really optional) and Acoustic Elegance TD15H+ woofer in a 5 cuft vented box tuned to ~21 Hz. The woofer is powered by a big amp w/dsp and the mid/tweeter are powered by my own EL34 SET amp. I set them up fairly wide with a lot of toe-in and listen almost nearfield. The main goal, and luckily the result, is a system that is extremely immersive with a very wide and deep "you are there" soundstage. Polar plot is near perfect.
 

Duke LeJeune

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#19
I'll try again on this one, lol... The options here are spectrally correct 1st reflections being present vs a speaker with directionality that avoids 1st reflections.
Okay, if by "first reflections", you mean the typical suite of relatively early first reflections (floor, ceiling, nearby sidewalls), then I THINK I finally understand!

I think it's a tradeoff. If early reflections are generally undesirable and late reflections desirable, then in general a wide pattern speakers = lots of early reflections + lots of late reflections; and a narrow-pattern speaker = much fewer early reflections + some (but not as much) late reflections.

A fairly narrow-patttern dipole or bipole can, with suitable positioning, do a "best of both worlds": Few early reflections + lots of late reflections.

What I do is arguably a variation on the bipolar theme: Fairly narrow (typically 90 degrees over most of the spectrum) direct sound with additional upwards-and-backwards directed reverberant energy from a secondary array, the idea being to get a fairly long path length without needing to position them so far out into the room.

My speaker is a wideband driver in a ~300 Hz LeCleach Horn, a Fostex T500A super tweeter (that's really optional) and Acoustic Elegance TD15H+ woofer in a 5 cuft vented box tuned to ~21 Hz. The woofer is powered by a big amp w/dsp and the mid/tweeter are powered by my own EL34 SET amp. I set them up fairly wide with a lot of toe-in and listen almost nearfield. The main goal, and luckily the result, is a system that is extremely immersive with a very wide and deep "you are there" soundstage. Polar plot is near perfect.
VERY NICE!! Yup, with a wideband driver on a big LeCleach horn, lots of toe-in and "almost nearfield", you have pretty much eliminated the first reflections.

Here's a weird idea: Assuming your wideband driver goes up high but narrows a bit on-axis, you might try aiming the T500A backwards. This way there is no time-domain disturbance to the first-arrival sound from having a second driver involved up high, but the T500A will still be improving the tonal balance via its contribution to the reverberant field. You might need to turn up the level of the T500A a bit.
 
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DaveC

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#20
Okay, if by "first reflections", you mean the typical suite of relatively early first reflections (floor, ceiling, nearby sidewalls), then I THINK I finally understand!

I think it's a tradeoff. If early reflections are generally undesirable and late reflections desirable, then in general a wide pattern speakers = lots of early reflections + lots of late reflections; and a narrow-pattern speaker = much fewer early reflections + some (but not as much) late reflections.

A fairly narrow-patttern dipole or bipole can, with suitable positioning, do a "best of both worlds": Few early reflections + lots of late reflections.

What I do is arguably a variation on the bipolar theme: Fairly narrow (typically 90 degrees over most of the spectrum) direct sound with additional upwards-and-backwards directed reverberant energy from a secondary array, the idea being to get a fairly long path length without needing to position them so far out into the room.



VERY NICE!! Yup, with a wideband driver on a big LeCleach horn, lots of toe-in and "almost nearfield", you have pretty much eliminated the first reflections.

Here's a weird idea: Assuming your wideband driver goes up high but narrows a bit on-axis, you might try aiming the T500A backwards. This way there is no time-domain disturbance to the first-arrival sound from having a second driver involved up high, but the T500A will still be improving the tonal balance via its contribution to the reverberant field. You might need to turn up the level of the T500A a bit.

Yes, in my testing people always prefer my horns to my Pioneer S-1EX (Same drivers as TAD Evolution Tower) and modded Odyssey Stratos amp, and the reason for the preference is the greater sense of immersion from the horns. But, I also think it takes some time to acclimate to the horns greater ratio of direct to reflected sounds and the near absence of 1st reflections. I think preference can change with experience and hearing lots of different systems so you're not as acclimated to one particular system.

One other factor is my room is not a fully treated and dedicated room, it has some absorption to adjust decay times, but is more like a typical living room, so the conventional speakers are at a disadvantage vs a dedicated room. It has high ceilings which I never want to be without again, it's a big advantage over 8ft ceilings. Anyways, with a dedicated room I've heard conventional speakers do a great job with immersion as well, so I'm thinking those early 1st reflections can work if the acoustic space is more ideal, otherwise you're probably better off with a speaker that avoids producing them in the 1st place.

So for me, I see a big difference in design for a speaker that is intended to be used in a dedicated space vs a living room. It may well be in a dedicated room a big cone n dome with wide dispersion is just as good as any other solution, while a speaker with narrow dispersion is, at least to me, the best choice for a non-ideal space.

I've tried a lot of stuff with the tweeter in my own speaker as well as running the mids with an open back as well as a back stuffed with different thicknesses of reticulated foam... But for my room size the best sound I got was with a closed back as long as internal reflections in the cabinet were handled properly. I only have about 3ft behind the speaker so the rear wave wasn't delayed enough to work. For the tweeter, it's crossed over really high up and aligned with the mids, it's completely transparent and seamless. My mid driver covers all the way to 15 kHz so the tweeter may not even be heard by some. I can still hear CRT flyback at 18 kHz so I appreciate the super tweeters. :)
 

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