Frontal reflections, depth of soundstage, and dipoles

[Bugal1998]

You will probably laugh, Madonna the Immaculate collection is an obvious example. The whole disc sounds like it was recorded in surround sound or something. Most other times I heard it, it was just a tiny portion in the song, there’s a Pink Floyd song can’t think of the song right now, where a laughing man’s voice sounds like it’s right at your head

Yeah, the QSound processing on that Madonna album is striking!

I’m not sure if you would find Madonna’s music engaging, but hey you asked.

It's not in regular rotation, but I have fun using it for demo material... thanks for sharing!

I’m always fixing grammar errors, my writing skills are terrible, but it doesn’t stop me from posting.

Oh man, my posts can be disastrous at times. Using my phone doesn't help.

Ah, that’s how plane is spelled, not plain as I have wrote it in all the previous posts.

Well that's how I spelled it, but that doesn't mean it's right!

 

[goat76]

Excellent question!

The listening room cannot make a distinction between the reflections on the recording and its own native reflections, but our ear/brain systems can!

The ear/brain system can tell which first-arrival sound a given reflection goes with by looking for overtone sequences that match up. So when an overtone sequence from the reverberation in the recording arrives after multiple in-room bounces, the ear/brain system still knows which first-arrival sound it goes with, assuming it is spectrally correct and still loud enough to be detected.

And imo this is why we want to preserve the spectral balance of the in-room reflections: Once they have lost too much of their high frequency energy to be identifiable by their overtones, they cease to be "signal" and become effectively "noise". If you've ever gotten listening fatigue from listening in an overdamped room, this might be why.

Yes, but I still think you miss the main point I'm trying to make here.

I understand that our brain can distinguish between the first-arrival sound (the direct sound from our loudspeakers) and the late-arrival sound (the reflections from our listening environment). But still, when you talk about your theory that the listening room would act as a carrier for the reflections (in particular) in the recording, you make a distinction between the direct sounds in the recording vs the reflections in the recording.

The problem with your theory of "carrier of reverberation tails" is that the listening room will never make any distinction at all between the direct sounds in the recording vs the reflection sounds in the recording. Instead, the listening room will "smear" everything together no matter if it is a direct sound in the recording or a reflection sound in the recording.

Do you see the problem with your theory?
How can the room act as a carrier for the reverberation tails (in specific) in a recording, when the room, from a reflection point-of-view, can never make any distinction at all between the recorded direct sounds and the recorded reflections?

In short: We must make a distinction between the stereo illusion we hear vs what the room sees, which are only two sound-generating point sources in the room from a reflection point of view.

 

[Duke]

Yes, but I still think you miss the main point I'm trying to make here.

I understand that our brain can distinguish between the first-arrival sound (the direct sound from our loudspeakers) and the late-arrival sound (the reflections from our listening environment). But still, when you talk about your theory that the listening room would act as a carrier for the reflections (in particular) in the recording, you make a distinction between the direct sounds in the recording vs the reflections in the recording.

The problem with your theory of "carrier of reverberation tails" is that the listening room will never make any distinction at all between the direct sounds in the recording vs the reflection sounds in the recording. Instead, the listening room will "smear" everything together no matter if it is a direct sound in the recording or a reflection sound in the recording.

Do you see the problem with your theory?
How can the room act as a carrier for the reverberation tails (in specific) in a recording, when the room, from a reflection point-of-view, can never make any distinction at all between the recorded direct sounds and the recorded reflections?

In short: We must make a distinction between the stereo illusion we hear vs what the room sees, which are only two sound-generating point sources in the room from a reflection point of view.

The reverberation tails in the recording will last a lot longer (and therefore continue to deliver cues to the listener for a lot longer) than either the direct sound OR the playback-room reflections of the direct sound, because they are being injected into the reflection field via the in-room reflections - the "carriers" - long after the in-room reflections of the direct sound have faded into inaudibility. And the in-room reflections deliver those reverberant tails from many different directions, which mimics reality far better than if the reverberation tails arrived only from the exact same direction as the first-arrival sound.

It sounds to me like the "smearing" of which you speak envisions the ear/brain system blending the room's spatial signature with the recording venue's spatial signature. I admit that this makes intuitive sense, and perhaps it does happen in some situations, but let me ask you this: Have you ever heard a system that produces a convincing "you are there" presentation, wherein the sense of space changes significantly from one recording to the next? I assume you have. The only way this could happen is if the ear/brain system can separate out the venue spatial cues from the playback room's spatial cues, and accept the former as the more plausible package of cues. Here is one way that I have experienced a "you are there" presentation:

I was investigating positioning strategies for the big fullrange dipole electrostats I sell, so that I could advise customers on whether or not they would work well given their particular placement constraints. I started with the speakers very close to the front wall and moved them out from the wall in one-foot increments. The soundstage got noticeably but not hugely deeper with every additional foot forward from the wall, until the distance got to about five feet. At this point, the soundstage transitioned from incrementally deeper to "you are there", extending very deep if the recording called for it. Simultaneously there was a sense of immersion in a recording-appropriate acoustic space that changed significantly and enjoyably from one recording to the next. What I THINK happened is, a threshold was crossed and the "recording venue package of spatial cues" became perceptually dominant over the "playback room package of spatial cues".

This "package of cues" paradigm is unconventional, so let me offer an illustration of the ear/brain system accepting a "package of cues" rather than a "blending and smearing of cues". These won't be spatial packages of cues so this is not a direct example of what I'm talking about, but it does illustrate the ear/brain system selecting one "package of cues" over another.

Click on this video and you will hear two packages of cues presented simultaneously. One package of cues is the word "yanny". The other package of cues is the word "laurel". Both packages of cues are simultaneously present but for reasons I won't go into the ear/brain system selects one as the dominant package of cues, instead of "smearing everything together":

 

[Chromatischism]

In my own subjective anecdotal experience, I wasn't satisfied with the sound quality of my (monopolar) speakers until they were 1) pulled out a couple of feet from the front wall and 2) had 4" broadband absorbers placed behind them. Sound quality and harshness were cleaned up quite a bit by eliminating/attenuating those reflections, and imaging became more pinpoint.

 

[Bugal1998]

Imagine your speakers direct sound disappeared suddenly, what would it sound like to have just the early reflections and later room sound left?

Luckily later reflections, that have bounced multiple times from boundaries start to be more balanced, coming from all directions, so in this sense much more surrounding as there is no distinct hot spot where they seem to emerge, but everywhere.

I have kinda done part of this experiment. If I walk up past the plane of the speakers, all direct sound from the speakers becomes imperceptible and only late(er) reflections (48 ms minimum delay... and diffused) can be heard. The sound is tonally pleasing but completely diffuse, coming from everywhere. From behind the speakers it's hard to imagine the sound when sitting in the room would be anything but completely enveloping. As soon as I move back close enough to the plane of the speakers to hear the direct sound again, the room sounds much less enveloping. The direct sound dominates.

Now I need to go listen from behind the speakers and see if I can hear any depth cues...

 

[Bugal1998]

My room was designed by a Home Acoustics Alliance certified designer, and I have to say, they delivered on the experiences outlined here: https://homeacoustics.org/acoustical-focus-and-envelopment/

The concepts described, while having less detail than @Duke 's articulation do align with the same general premise of late reflections being beneficial. They have some slightly more nuanced definitions, so it may be worth reading the entire article, but the relevant content starts in the paragraph beginning with, "If it’s that simple, why do so many systems still lack scary good focus?"

A story...

I was accustomed to a more damped room that yielded a very direct and hyper focused sound, and I told the designer that I wanted to experience the unique acoustic space of each recording. During the design phase I was concerned with 1) how relatively little absorbtion was in the room overall, and 2) that the early reflections were mostly diffused or reflected and not absorbed. I shared my concerns and asked the designer what he thought, and he chuckled slightly and said, "I think you'll be blown away."

And I was! Eventually.

When I played the very first song I was straight up dissapointed. Dissapointed with how distant and initially unimpressive it sounded (I now appreciate the tremendous depth). But I quickly came to be in awe of the width, spaciousness, ambiance, and envelopment that I was hearing and experiencing. The article linked above mentions debates about which experience is better, more focus or more envelopment. I was an unabashed 'focus guy', but after playing through my library in the new space, I became a full on convert to an 'envelopment guy'; I want just enough focus to clearly place voices, instruments, and sounds without any ambiguity, and from there "maximize the envelopment please!" The acoustic beauty of the track-to-track ambiance completely won me over. There's just no going back!

So to the thread topic, I don't believe frontal reflections are particularly important to the creation of depth. Depth is in the recording, but also enhanced by a diffuse sound field for the late reflections.

Final thoughts...

In my experience, a low noise floor in the room, neutral frequency response, and lack of audible speaker resonances and distortions further enable the perception of depth during playback.

 

[Duke]

I was accustomed to a more damped room that yielded a very direct and hyper focused sound, and I told the designer that I wanted to experience the unique acoustic space of each recording. During the design phase I was concerned with 1) how relatively little absorbtion was in the room overall, and 2) that the early reflections were mostly diffused or reflected and not absorbed. I shared my concerns and asked the designer what he thought, and he chuckled slightly and said, "I think you'll be blown away."

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

By not absorbing the first reflections, but either reflecting them (presumably not directly towards the listening area) or diffusing them, that energy not only survives to become late-arriving reflections, but it also retains its original spectral balance (or very nearly so; some attenuation of the shortest reflected wavelengths is inevitable).

When I played the very first song I was straight up dissapointed. Dissapointed with how distant and initially unimpressive it sounded (I now appreciate the tremendous depth). But I quickly came to be in awe of the width, spaciousness, ambiance, and envelopment that I was hearing and experiencing. The article linked above mentions debates about which experience is better, more focus or more envelopment. I was an unabashed 'focus guy', but after playing through my library in the new space, I became a full on convert to an 'envelopment guy'; I want just enough focus to clearly place voices, instruments, and sounds without any ambiguity, and from there "maximize the envelopment please!" The acoustic beauty of the track-to-track ambiance completely won me over. There's just no going back!

"You are there" (envelopment) is a different presentation than "they are here" (focus), and obviously which to prioritize is a matter of personal preference. But I THINK it is the suppression of early reflections combined with the preservation of the late reflections that enables "you are there", assuming there are no distracting colorations.

Perhaps the "you are there" mechanism is not what I have presumed (namely that the late reflections function as "carriers"), but ime following that paradigm seems to give good results.

 

[tmuikku]

...

I was investigating positioning strategies for the big fullrange dipole electrostats I sell, so that I could advise customers on whether or not they would work well given their particular placement constraints. I started with the speakers very close to the front wall and moved them out from the wall in one-foot increments. The soundstage got noticeably but not hugely deeper with every additional foot forward from the wall, until the distance got to about five feet. At this point, the soundstage transitioned from incrementally deeper to "you are there", extending very deep if the recording called for it. Simultaneously there was a sense of immersion in a recording-appropriate acoustic space that changed significantly and enjoyably from one recording to the next. What I THINK happened is, a threshold was crossed and the "recording venue package of spatial cues" became perceptually dominant over the "playback room package of spatial cues".
...

Hi, how was your listening position with this experiment? did you keep it stationary relative to room or speakers?

I have hypothesis that the front wall distance doesn't matter much at all regarding this effect, and all that matters is how far the listener is from speakers. Basis for the hypothesis is that front wall is one source of early reflections and there are many in a room. Reducing listening distance changes all early reflections in relation to direct sound, not just that from the front wall but floor and ceiling and all others. So if listening spot is kept stationary, all reflections change when speakers are brough further from front wall = closer to listener.

The front wall will have some effect for sure, so just trying to get some extra info from your experiment.

 

[tmuikku]

I have kinda done part of this experiment. If I walk up past the plane of the speakers, all direct sound from the speakers becomes imperceptible and only late(er) reflections (48 ms minimum delay... and diffused) can be heard. The sound is tonally pleasing but completely diffuse, coming from everywhere. From behind the speakers it's hard to imagine the sound when sitting in the room would be anything but completely enveloping. As soon as I move back close enough to the plane of the speakers to hear the direct sound again, the room sounds much less enveloping. The direct sound dominates.

Now I need to go listen from behind the speakers and see if I can hear any depth cues...

Here is one experiment how to remove early reflections in traditional sense, and it's a weird sound:
Go sit into a corner, looking to the room, position your speakers against the walls that make the corner and quite near to you, pointing toward you, toward the corner.

Weird it is as the envelopment isn't that great as one is in a corner, but fun way to "see the sound in your room" in a way, get another perspective on sound in a room. And bass modes

... that the early reflections were mostly diffused or reflected and not absorbed. ...

This is a mixing knob in my thought experiment, energy of early reflections is reduced and later reflections increased. What you describe in your post makes a lot of sense.

 

[dweeeeb2]

Here is one experiment how to remove early reflections in traditional sense, and it's a weird sound:
Go sit into a corner, looking to the room, position your speakers against the walls that make the corner and quite near to you, pointing toward you, toward the corner.

I like that, will try one day, thanks!

 

[tmuikku]

I like that, will try one day, thanks!

Sorry almost of topic, but since you are interested I'll expand a bit:
I had two person sofa tucked into a corner in 45deg angle, and speakers basically over the handrests near the walls, so I wasn't sitting that deep into the corner, but close enough seems fine. Back of the sofa was likely eliminating first reflections from corner behind me, and seat of the sofa was in the way of floor reflection. Lean back and forward to change azimuth angle of speakers to you, and at some position the sound localizes inside the head just like with headphones, while the whole room seems to be just ambience, very weird stuff perceptually Removes front wall completely, also bass is very nice, all room effects gone in sense that it's stable at all/most frequencies. So, this is basically one helluva positioning, as anything is not middle of the room so it's very practical for family livingroom and sound is nice in theory, void of most room effects, but a weird one still I should revisit this experiment, as I don't remember paying attention to depth in particular, all I remember the ambience and localization inside the head, so perhaps depth wasn't there as such.

edit.
try this fun experiment I made with Desmos, where there is two sound sources and a "main listening postion" as in stereo listening triangle. Also two boundaries formed by x and y axis, the black lines. On the right is oscilloscope view of direct sound and reflections of both speakers from both boundaries, and their sum illustrating how direct sound and reflections interfere at listening spot. Blue sine wave is the sum at listening postion. Hit mute button to hear sound and play button on the frequency variable to make it sweep. Now you see and hear amplitude modulate at listening position due to the reflections interfering with direct sound. This attachment shows where to click to enable sound and frequency sweep:


You can now drag the main listening position and the speakers around with mouse and see / hear how the interference changes from the two boundaries, and it's quite obvious it's gonna wobble always, as there is two spurces and path lengths of reflections are relatively long. Unless, you put the MLP to the corner and speakers agaisn the boundaries to reduce reflection path lengths to effectively eliminate the reflections effect on bass, and now your sweep is steady. In a real room there is a lot more reflections and modes happen and all that, so it's just something to play with to build intuition on positioning, a fun experiment at least

 

[goat76]

The reverberation tails in the recording will last a lot longer (and therefore continue to deliver cues to the listener for a lot longer) than either the direct sound OR the playback-room reflections of the direct sound, because they are being injected into the reflection field via the in-room reflections - the "carriers" - long after the in-room reflections of the direct sound have faded into inaudibility. And the in-room reflections deliver those reverberant tails from many different directions, which mimics reality far better than if the reverberation tails arrived only from the exact same direction as the first-arrival sound.

I still find it unlikely that we will be able to hear the recorded reverb tails in the late-arrival diffuse field generated by the late reflections in the listening room.

When looking at the Filtered Impulse Response in my room (which is not over-dampened), the late reflections that arrive 60 ms after the direct response are 31 dB lower than the direct sound, while the early reflections are 20 dB lower. Let us now say that a recording where made in a much larger room than mine where the early reflections (the ones we hear as cues for the recorded space) are likely even lower, let's say 30 dB lower than the recorded direct sounds. That would mean that the recorded reverberation tales "carried" by the late reflections in my room would be 61 dB (31+30 dB) lower than the direct sound from my loudspeakers playing a continuous stream of music.

So with the above levels in mind, I think most (if not all?) we hear from those late reflections and the diffuse field (that adds the envelopment) is highly dominated by the direct sounds in the recording, and not much (or any) from the reverberation tales in the recording.

 

[Duke]

Hi, how was your listening position with this experiment? did you keep it stationary relative to room or speakers?

I have hypothesis that the front wall distance doesn't matter much at all regarding this effect, and all that matters is how far the listener is from speakers. Basis for the hypothesis is that front wall is one source of early reflections and there are many in a room. Reducing listening distance changes all early reflections in relation to direct sound, not just that from the front wall but floor and ceiling and all others. So if listening spot is kept stationary, all reflections change when speakers are brought further from front wall = closer to listener.

The front wall will have some effect for sure, so just trying to get some extra info from your experiment.

Ime the front wall distance matters a LOT with dipole speakers, which direct just as much energy towards the front wall as towards the listening area.

I would have kept the same listening triangle geometry but I do not have an actual recollection of moving my chair. The listening triangle that I preferred put my chair about eight feet (about 244 cm) from the plane of the speakers. These were seven foot tall (line-source-approximating) electrostats so their direct field extended further than it would have with conventional speakers.

You didn't mention Griesinger's "proximity" in so many words, but imo "proximity" and "envelopment" are not necessarily mutually exclusive in a playback setting, the key arguably being a significant time gap between the direct sound and the strong onset of reflections... which happens to be something big electrostats can do if given sufficient distance from the wall. I noticed the transition to "you are there" at 5 feet (about 152 cm) from the wall, and 7 feet (about 213 cm) seemed to be "optimum" to my ears, but unfortunately was not practical.

I still find it unlikely that we will be able to hear the recorded reverb tails in the late-arrival diffuse field generated by the late reflections in the listening room.

I have read - but unfortunately do not remember where - that the ear/brain system can detect reflections down into the noise floor, and it does so by following the overtone patterns, which would be another argument for their preserving their spectra.

... So with the above levels in mind

I cannot comment on the relative levels of direct and reflected sound assumed in your post; I simply do not know what would be "normal". If I understand correctly, you're saying that the reverberation tails on the recording are effectively inaudible in the playback room. Is this correct?

I think most (if not all?) we hear from those late reflections and the diffuse field (that adds the envelopment) is highly dominated by the direct sounds in the recording, and not much (or any) from the reverberation tales in the recording.

The direct sound in the recording contains no venue spatial cues, therefore reflections of the recording's direct sound in the playback room would ONLY have the playback room's spatial cues. So, the in-room reflections of the recording's direct sound cannot convey a "you are there" spatial quality.

The reflections (including the reverberation tails) in the recording are what contain the venue spatial cues, so any plausible "you are there" spatial quality must come from the reflections in the recording (for unprocessed two-channel).

Obviously the venue spatial cues are in the direct sound from the speakers. Does "you are there" arise solely from the direct sound from the speakers? Not in my experience, nor do I recall anyone describing a "you are there" experience listening to a normal speaker setup in an anechoic chamber. And my recollection from Toole's book is that the WORST direction for reflections to arrive from would be the exact same direction as the first-arrival sound.

So by process of elimination, the only thing left that could effectively enable a "you are there" spatial presentation are the venue spatial cues being carried by the playback room's reflections, and arriving from many different directions.

Now I could be wrong about it being the reverberation tails which enable "you are there"; maybe it's the earliest venue reflections arriving from many directions which enables "you are there", but the imo preferred course of action remains the same: Disrupt the "small room signature" of the playback room by minimizing the earliest reflections, while simultaneously promoting the effective presentation of the venue spatial cues via the later-arriving reflections.

 

[Sokel]

Ime the front wall distance matters a LOT with dipole speakers, which direct just as much energy towards the front wall as towards the listening area.

I would have kept the same listening triangle geometry but I do not have an actual recollection of moving my chair. The listening triangle that I preferred put my chair eight feet (about 244 cm) from the plane of the speakers. These were seven foot tall (line-source-approximating) electrostats so their direct field extended further than it would have with conventional speakers.

You didn't mention Griesinger's "proximity" in so many words, but imo "proximity" and "envelopment" are not necessarily mutually exclusive in a playback setting, the key arguably being a significant time gap between the direct sound and the strong onset of reflections... which happens to be something big electrostats can do if given sufficient distance from the wall. I noticed the transition to "you are there" at 5 feet (about 152 cm) from the wall, and 7 feet (about 213 cm) seemed to be "optimum" to my ears, but unfortunately was not practical.



I have read - but unfortunately do not remember where - that the ear/brain system can detect reflections down into the noise floor, and it does so by following the overtone patterns, hence another argument for their preserving their spectra.



I cannot comment on the relative levels of direct and reflected sound assumed in your post; I simply do not know what would be "normal". If I understand correctly, you're saying that the reverberation tails on the recording are effectively inaudible in the playback room. Is that correct?



The direct sound in the recording contains no venue spatial cues, therefore reflections of the recording's direct sound in the playback room would ONLY have the playback room's spatial cues. So, the in-room reflections of the recording's direct sound cannot convey a "you are there" spatial quality.

The reflections (including the reverberation tails) in the recording are what contain the venue spatial cues, so any plausible "you are there" spatial quality must come from the reflections in the recording (for unprocessed two-channel).

Obviously the venue spatial cues are in the direct sound from the speakers. Does "you are there" arise solely from the direct sound from the speakers? Not in my experience, nor do I recall anyone describing a "you are there" experience listening to a normal speaker setup in an anechoic chamber. And my recollection from Toole's book is that the WORST direction for reflections to arrive from would be the exact same direction as the first-arrival sound.

So by process of elimination, the only thing left that could effectively enable a "you are there" spatial presentation are the venue spatial cues being carried by the playback room's reflections, and arriving from many different directions.

Now I could be wrong about it being the reverberation tails which enable "you are there"; maybe it's the earliest venue reflections arriving from many directions which enables "you are there", but the imo preferred course of action remains the same: Disrupt the "small room signature" of the playback room by minimizing the earliest reflections, while simultaneously promoting the effective presentation of the venue spatial cues via the later-arriving reflections.

OK,I'm gonna add to the confusion here.
Some time after my room was finished and I got the speakers I choose and set up everything I called again the guys that fixed my room for a sanity check.

Amongst some other advises the one I can never wrap my head around was the following:
"get exactly between your speakers so they are just outside your shoulders and the ears at the acoustic center's height"
"There you must hear the male voices like they are hanging above your head.If they don't you have messed up something,move the speakers further apart from the wall"

I won't even try to start counting how many things add up here.

 

[Bugal1998]

But I THINK it is the suppression of early reflections combined with the preservation of the late reflections that enables "you are there", assuming there are no distracting colorations.

I also THINK you are correct. To that end, my speakers are set to a 50° listening angle (25° L and R), and toed in 10°; this places the MLP 15° off the direct-axis of the speakers. The speaker response has been coarsely EQ'd to restore the direct frequency response at the MLP (especially in the upper treble), resulting in slightly more energy in the speakers' on-axis output that bypasses both the listener and first sidewall reflections and makes its way into the diffuse soundfield of the late reflections. As an additional benefit, it also restores more of the total soundpower response of the speaker, which tends to beam above 9-10khz. I've been living with this arrangement for some months now and I'm very pleased with the results. Next step is to use anechoic data to generate precise eq filters instead of estimates and in situ measurements, and turn off all room eq frequency correction above the transition region.

 

[Blumlein 88]

Ime the front wall distance matters a LOT with dipole speakers, which direct just as much energy towards the front wall as towards the listening area.

I would have kept the same listening triangle geometry but I do not have an actual recollection of moving my chair. The listening triangle that I preferred put my chair about eight feet (about 244 cm) from the plane of the speakers. These were seven foot tall (line-source-approximating) electrostats so their direct field extended further than it would have with conventional speakers.

You didn't mention Griesinger's "proximity" in so many words, but imo "proximity" and "envelopment" are not necessarily mutually exclusive in a playback setting, the key arguably being a significant time gap between the direct sound and the strong onset of reflections... which happens to be something big electrostats can do if given sufficient distance from the wall. I noticed the transition to "you are there" at 5 feet (about 152 cm) from the wall, and 7 feet (about 213 cm) seemed to be "optimum" to my ears, but unfortunately was not practical.



I have read - but unfortunately do not remember where - that the ear/brain system can detect reflections down into the noise floor, and it does so by following the overtone patterns, which would be another argument for their preserving their spectra.



I cannot comment on the relative levels of direct and reflected sound assumed in your post; I simply do not know what would be "normal". If I understand correctly, you're saying that the reverberation tails on the recording are effectively inaudible in the playback room. Is this correct?



The direct sound in the recording contains no venue spatial cues, therefore reflections of the recording's direct sound in the playback room would ONLY have the playback room's spatial cues. So, the in-room reflections of the recording's direct sound cannot convey a "you are there" spatial quality.

The reflections (including the reverberation tails) in the recording are what contain the venue spatial cues, so any plausible "you are there" spatial quality must come from the reflections in the recording (for unprocessed two-channel).

Obviously the venue spatial cues are in the direct sound from the speakers. Does "you are there" arise solely from the direct sound from the speakers? Not in my experience, nor do I recall anyone describing a "you are there" experience listening to a normal speaker setup in an anechoic chamber. And my recollection from Toole's book is that the WORST direction for reflections to arrive from would be the exact same direction as the first-arrival sound.

So by process of elimination, the only thing left that could effectively enable a "you are there" spatial presentation are the venue spatial cues being carried by the playback room's reflections, and arriving from many different directions.

Now I could be wrong about it being the reverberation tails which enable "you are there"; maybe it's the earliest venue reflections arriving from many directions which enables "you are there", but the imo preferred course of action remains the same: Disrupt the "small room signature" of the playback room by minimizing the earliest reflections, while simultaneously promoting the effective presentation of the venue spatial cues via the later-arriving reflections.

I have found the same thing over and over with panel speakers in many different room configurations. I tell people if they don't have the ability to have 60 inches behind the panel not to bother.

I do know of one way you can violate the 60 inch (1.5 meter) rule. If you have a long wall behind the speakers and can place the speakers at an angle so the rear reflection travels at least 60 inches (1.5 meters) before hitting the side wall you can get away with only being 20-30 inches from the rear wall. For example I once had a setup with a 20 foot wall behind the speakers. I was sitting across the short dimension of the room. I placed some ESL's about 8 feet apart with the most rear edge about 24 inches from the wall. Angled in toward the LP. That worked just fine though the greater angling reduced the sweet spot.

 

[Duke]

I do know of one way you can violate the 60 inch (1.5 meter) rule. If you have a long wall behind the speakers and can place the speakers at an angle so the rear reflection travels at least 60 inches (1.5 meters) before hitting the side wall you can get away with only being 20-30 inches from the rear wall. For example I once had a setup with a 20 foot wall behind the speakers. I was sitting across the short dimension of the room. I placed some ESL's about 8 feet apart with the most rear edge about 24 inches from the wall. Angled in toward the LP. That worked just fine though the greater angling reduced the sweet spot.

Yes! That totally works!!

 

[Bugal1998]

So by process of elimination, the only thing left that could effectively enable a "you are there" spatial presentation are the venue spatial cues being carried by the playback room's reflections, and arriving from many different directions.

Apologies, the quotes are in reverse order...

I still find it unlikely that we will be able to hear the recorded reverb tails in the late-arrival diffuse field generated by the late reflections in the listening room.

I always have the acute sense that I'm not nearly informed enough in these types of conversations. But allow me to propose another idea nonetheless.

Is it possible that the phase information in the direct [listening]-axis signal also plays a role in how the brain processes information in the "diffuse" late reflections? In the direct signal there is the direct sound of the venue which is typically played back more or less in phase in the left and right speakers. Then there is the reverb and ambiance which tends to be out of phase. Since the late reflections are more likely to come from a variety of directions (including from behind) in a typical room, is it possible that the mere presence of out of phase reverb in the [direct listening axis] sound tricks the brain into treating some of the direct in phase sound as ambiance when it later arrives from random directions and with random phase?

It should be possible to test this hypothesis with a track that has stereo mono reverb in phase, and then the identical reverb but mixed out of phase. If the hypothesis is correct then significantly more reverb should be detected in the second scenario.

Or [reinsert first sentence here].

Edit: In other words, does the brain 'mistakenly' integrate some of the volume level of the direct [venue] sound [which is heard in both the direct sound from the speaker and later in the room's diffuse field] into the [room's diffuse] reverb and ambiance, increasing the perceived level of ambiance?

Edit 2: Words in closed brackets were edited for clarity.

 

[goat76]

I have read - but unfortunately do not remember where - that the ear/brain system can detect reflections down into the noise floor, and it does so by following the overtone patterns, hence another argument for their preserving their spectra.

That may be correct, but I think a very important factor in detecting those low-level reflections, and for us to separate them from the direct sound, has much to do with hearing different directional cues. Those different directional cues can only be heard in the stereo illusion, but will not be present in reverberation that occurs in the listening environment as those reflections are generated by the two speakers and by that have lost the directional cues present in the stereo illusion.

I cannot comment on the relative levels of direct and reflected sound assumed in your post; I simply do not know what would be "normal". If I understand correctly, you're saying that the reverberation tails on the recording are effectively inaudible in the playback room. Is that correct?

Yes and no.

I believe the reverberation tails in the recording are only heard in the direct sound, which represents the stereo illusion where the directional cues are present.

But I believe the reverberating tails from the recording get completely lost in the diffuse reverberation field (that we hear as envelopment), and that is just a "mess" of everything in the recording as there are no longer any differences when it comes to directional cues, as everything (recorded direct sounds and recorded reflections) are now generated from only two positions, the position of the two loudspeakers.

The direct sound in the recording contains no venue spatial cues, therefore reflections of the recording's direct sound in the playback room would ONLY have the playback room's spatial cues. So, the in-room reflections of the recording's direct sound cannot convey a "you are there" spatial quality.

Yes, that is what I believe...
The true spatial information can only be heard in the stereo illusion which can only come with the direct sound. We hear the recorded room from the "outside" in front of us, and the envelopment (the "mess") added by the late reflections from our listening room gives us the sensation of "being there".

The reflections (including the reverberation tails) in the recording are what contain the venue spatial cues, so any plausible "you are there" spatial quality must come from the reflections in the recording (for unprocessed two-channel).

All those spatial cues (the reflections including the reverberation tails) come with the direct sound and are included in the stereo illusion that the two well-set-up loudspeakers in a not-too-lively listening room "paint" for us.

Obviously the venue spatial cues are in the direct sound from the speakers. Does "you are there" arise solely from the direct sound from the speakers? Not in my experience, nor do I recall anyone describing a "you are there" experience listening to a normal speaker setup in an anechoic chamber. And my recollection from Toole's book is that the WORST direction for reflections to arrive from would be the exact same direction as the first-arrival sound.

Not in my experience either...
As I see it, the direct sound information can only give us a "from the outside view" into the recorded venue, and the rest that gives us the sensation of envelopment and the "you are there" sensation doesn't have to be much more than a diffuse sound, the "mess".

So by process of elimination, the only thing left that could effectively enable a "you are there" spatial presentation are the venue spatial cues being carried by the playback room's reflections, and arriving from many different directions.

I know that I'm repeating the same thing, but the "venue's spatial cues" are no longer a separate thing from the recorded direct sounds of the instruments played in that venue. From the perspective of the reflections that will occur in the listening room (which will give us the sensation of envelopment), everything is now generated by only two sound sources which will prevent any distinctions between recorded reflections and recorded direct sounds. The listening room will only "see" the two sound sources and not anymore the stereo illusion. As the directional cues are now lost when there is no longer a stereo illusion and everything is now coming from the same directions as a "package", it will now be dominated by the strongest sound which is the direct sounds in the recording and the reverberation tails will be lost in the "mess".

Now I could be wrong about it being the reverberation tails which enable "you are there"; maybe it's the earliest venue reflections arriving from many directions which enables "you are there", but the imo preferred course of action remains the same: Disrupt the "small room signature" of the playback room by minimizing the earliest reflections, while simultaneously promoting the effective presentation of the venue spatial cues via the later-arriving reflections.

I could also be wrong in my theories, but the thing I'm quite sure about is that the reflections that occur in the listening room can never make any distinctions of what is in the stereo illusion, the room only "sees" two sound sources from a reflection-generating point of view.

 

[goat76]

Apologies, the quotes are in reverse order...

I always have the acute sense that I'm not nearly informed enough in these types of conversations. But allow me to propose another idea nonetheless.

Is it possible that the phase information in the direct on-axis signal also plays a role in how the brain processes information in the "diffuse" late reflections? In the direct signal there is the direct sound of the venue which is typically played back more or less in phase in the left and right speakers. Then there is the reverb and ambiance which tends to be out of phase. Since the late reflections are more likely to come from a variety of directions (including from behind) in a typical room, is it possible that the mere presence of out of phase reverb in the on-axis direct sound tricks the brain into treating some of the direct in phase sound as ambiance when it later arrives from random directions and with random phase?

It should be possible to test this hypothesis with a track that has stereo mono reverb in phase, and then the identical reverb but mixed out of phase. If the hypothesis is correct then significantly more reverb should be detected in the second scenario.

Or [reinsert first sentence here].

Edit: In otherwords, does the brain 'mistakenly' integrate some of the volume level of the direct sound into the reverb and ambiance, increasing the perceived level of ambiance?

If things are out of phase in the recording, any widening or envelopment effects that may occur will come exclusively with the direct sound, and be part of the stereo illusion that tricks your hearing that things are coming from positions outside the speakers. It will most likely not have any significant effect on the diffuse late reflections that occur in the listening room.


Just a side note:
I don't know exactly what you mean when you say "on-axis direct sound", as "on-axis" and "direct sound" have nothing in common. No matter in what direction you point your loudspeakers relative to the listening position, the "direct sound" will always be the straight path between you and the loudspeaker.