complete beginner starting treatment behind AT projector screen.

[DanDan]

LOL, Matt, I am not seeing any evidence of your claims.
"Envelopment or spaciousness are defined acoustic terms" Not sure where and in what way they are defined, but such words are in common usage. But perhaps not common meaning or understanding. Here Griesenger dismisses Sat/Sub systems and the notion of small room contributions.

Not everyone experiences Anechoic, but many of us work in environments quite close to it. Also anyone can put on headphones and listen to an ambience rich recording without a room contribution.
I used the word immersive, unknowing of any real definition. I would be happy to replace that with the word envelopment.

I am sure we can all agree with Griesenger and the Grammy Engineers in that a full proper surround system in a range of spaces from Anechoic, Non Environment, to Hemi Anechoic, will envelop/immerse/soak,swim, the listener in the original recording space more than two channel. However Stereo does indeed create a Sound FIELD. Also Dirac and others are working on Headphone surround.

 

[Matthew J Poes]

LOL, Matt, I am not seeing any evidence of your claims.
"Envelopment or spaciousness are defined acoustic terms"
View attachment 29159
Anyone can put on headphones and listen to an ambience rich recording. Claiming this is not 'immersive' doesn't make it so. Certainly a full proper surround system in an anechoic space will envelop one in the original recording space more. However, Dirac and others are working on that......

I'm suprised to hear you say this. You are suggesting nobody has researched this? It's been highly controversial, and most of the nay-sayers have clearly never read the research.

Ok I'll provide links. Many of the older articles are only available to AES members, but Toole has summarized many of them in his book.

Your proof comes from David Griesinger, and he won't agree with your use out of context of his claim. It's true that small rooms don't provide a lot of envelopment on their own, because they typically don't have a lot of reflections and those reflections are typically too short. What I said originally was only MCH can truly reproduce these effects, but a 2-channel room can be made to partially trick the ear. Toole also states that the music ultimately dominates our sense of space, but that isn't the same as claiming that a 2-channel system can reproduce all of that information. Just that a small room is too small to sound like a big room, no matter how much you treat it.

First source is obviously going to be Toole's book:

Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms (Audio Engineering Society Presents): Toole, Floyd: 9781138921368: Amazon.com: Books

Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms (Audio Engineering Society Presents) [Toole, Floyd] on Amazon.com. *FREE* shipping on qualifying offers. Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms (Audio Engineering Society...

www.amazon.com

Toole notes in Chapter 7 that defects in the perception of space was responsible for the majority of differentiation between speakers, that the speakers directivity and the rooms absorption level impacts a perception of space. He builds up this claim using a series of studies.

First we have the very controversial (for some) study by Kishinaga et al (1979)

1. Listening for defects in audio products, absorption prefered
2. enjoying the music, reflective environment prefered
3. Inter-aural Cross Correlation Coefficient measurements (highly correlated with both our perception of spaciousness and ASW) found that higher sidewall reflections reduced the ICCC, and the first sidewall reflections were found at 4 and 8 ms, which was associated with a more pleasing listening experience.
4. http://www.aes.org/e-lib/browse.cfm?elib=2830

Toole then sites Suzuki (1989) who explores the relationship between ICCC and perceptions of space, found:

1. stereo reproduction in a reflection free zone is incapable of reproducing the spacial components of a concert hall
2. https://www.ncbi.nlm.nih.gov/pubmed/2925994

Now it makes sense that since absorbers and diffusers do not eliminate reflections but just turn down the volume, so to speak, means that some of that information is still reaching the brain. It also means that the speaker must play a role in this, that a speakers directivity matters and in two ways. One is the strength of the reflections reproduced, which can be changed by changing the level of the directivity index (narrower dispersion) and second by ensuring that the reflections have the same tonal characteristics of the direct sound, which requires an even response and thus a smooth DI. Toole of course investigated this in his 1985 paper, where he finds:

1. Large differences in spatial quality were found even with monophonic speakers and this is tied to the speakers dispersion
2. On page 179 of his book he notes that: "Comb filtering is thought to be involved in all delayed sounds. However, a delayed sound arriving from a different horizontal angle than the direct sound is perceived as spaciousness, not comb filtering. It adds to the information about the room. It may also do more."
3. Toole continues to point out the relationship between spatial perception and ICCC, which again had been shown to be lower with more reflections and that these reflections are quite early at just 4 and 8 ms.

I would add above that I have measured 100's of rooms and have found that the two lateral early reflections happen anywhere from 1ms (speaker next to the wall) to 8ms for the closest wall and 5ms to 21ms for the farther wall first reflection across my own measurements. Obviously room size is what determined the differences. All of these numbers fall within the 25-30ms integration zone, yet still are being associated with a sense of spaciousness and space.

Toole also notes the experiences he had with "in-head localization" happening in highly absorbent rooms. That is my experience too.

Choisel (2005) is the next citation Toole gives and is a study using B&O wide dispersion speakers with B&W as narrower dispersion (though I would argue both of these are wide, but one is omnidirectional) and the combined or interactive role of wall treatment. They found:

1. reflections had no impact on the accuracy with which panning could be detected
2. The 50mm absorbers used in their testing didn't significantly reduce reflection strength compared to the 25mm panels used in the Kishinaga et al study, reinforcing Toole's point that single point reflection absorption will differ dramatically from what random incident testing would suggest. I too have found this to be true.
3. https://www.researchgate.net/public..._sound_quality_-_a_review_of_existing_studies

As a note to above, its this experience that I have had as well as Toole's findings and those of Kishinaga and Choisel that led me to prefer reflection control through speaker directivity. I operate an acoustics company so obviously I use absorption, but I look at the end result as a function of all of this and my personal preference is narrow dispersion for multichannel where I desire to reduce room interactions.

Finally was the Klippel (1990) study, which found:

1. Speaking of "naturalness" 50% was related to a feeling of space
2. Speaking of pleasantness 70% was associated with a feeling of space
3. Perceptions of space are related substantially to lateral reflections
4. A figure is included in the book that shows that for music, speech, and mixed content, it was desirable that the total reflected sound be 2-6dB's louder than the direct sound, music being most desirable to have the strongest reflections relative to direct sound
5. https://www.ingentaconnect.com/content/dav/aaua/1990/00000070/00000001/art00007
6. http://www.aes.org/e-lib/browse.cfm?elib=5765

And then we have all the associated research into the effects of reflection on perception for normal and impaired listeners:

Spectral and temporal integration of brief tones

Both spectral and temporal integration of tones have been explored in detail, but integration of tones varying across both dimensions has received little attention. This study explores temporal integration of tone pulses that vary over a range of frequencies. ...

www.ncbi.nlm.nih.gov

and this article does a nice job pulling together the theory and findings with subjective experience in developing aurlization models:

Integrating Real-Time Room Acoustics Simulation into a CAD Modeling Software to Enhance the Architectural Design Process

For architects, real-time 3D visual rendering of CAD-models is a valuable tool. The architect usually perceives the visual appearance of the building interior in a natural and realistic way during the design process. Unfortunately this only emphasizes the role of the visual appearance of a...

www.mdpi.com

Is that enough proof that my ideas are not unique to me and supported by evidence? Can you provide the same level of articles to counter this view? I've looked and I can't find them.

 

[Matthew J Poes]

@DanDan Wait I just caught in your first post that Boggy is no longer with us? I totally missed that. I'm sorry to hear that. This is off topic so lets talk offline, but that is sad to hear.

 

[DanDan]

"Is that enough proof that my ideas are not unique to me and supported by evidence? Can you provide the same level of articles to counter this view? I've looked and I can't find them"
One would need to take the ideas one by one and test them. Thing is, mostly or all, I have. I have provided Griesenger's direct contradictions on the subject of Envelopment and Immersion to no avail. Now the chat has turned to 'Space' Far out.
So I see no point in continuing with a facile game of waving other peoples willies! I stand by my empirical observations many of which can be easily corroborated pretty easily.


It should be remembered that I come from the world of producing music. Over a lifetime in audio one notices repeating phenomena.
Particularly ones that cause problems or ones that are notably beneficial.
A couple of decades ago I began to look for reasons for such phenomena. Enter a formal Study of Acoustics.
This has delivered.
e.g. The vast majority of CRs I have worked in, different countries, sounded too bright ( in the Direct Field.) This causes Dull Mixes.
These CR's were designed by engineers, architects, etc. who worked on a singular theory. i.e. the goal of the studio and speakers is to hear what is in the recording.
That is a false goal, easily achieved by listening to flat response speakers in NE, Anechoic CRs. It sounds horribly bright which does not represent any real listening experience other than say Audiometric Headphones. It causes inverse biased mixes which do not translate in any way to real life.
At least now I know why and what to do about it.

A lot of my work has been done in temporary locations. I used to place speakers hampered by common wisdom. i.e. Not near boundaries.
The thinned tonality attracted my ear...... Hi Fi types call it better imaging, depth and such. It is not, but rather a thinner tonality emphasising those higher frequency phenomena.
This lead to very LF heavy mixes.
When studying, and using my studio, Acoustic knowledge gave me the freedom to dump the common wisdom, to move speakers to touching the Front Wall.
The measured response is very obviously improved. Quite quickly I became used to hearing a proper LF response rather than the usual one. I recommend it to y'all.

This has delivered in spades. Including use of B&K, my work now has the same tonal balance anywhere. from the almost anechoic CR, to other systems in other rooms here, and on HD650s.
There is research and world class studio designers which vehemently diss such a notion. There are plenty of theoretical notions which contradict reality. Then there are the empirical facts.
A more solid type of 'knowing'.
Toole and Olive acknowledge the Circle of Confusion. They have researched and theorised this in hundreds of thousands of words and images. They could have just asked!

To my ears a stereo sound field is best sustained on headphones. Particularly a real one involving Binaural or M/S, but also ones we create using delays. Imaging is sharp. Resolution is good. Second best would be speakers in a Zone Without Early Reflections.
I know this because I have added side reflections by removing absorption, and electronically using 4.0 Reverbs and 4-5 Full range speakers.
It is a bit of fun, but a bit fuzzy if you want to make out what is going on in the recording. Also there are vast differences for instance between placing a Lead vocal in the Centre, or in LR, or LCR.
One solid source is the most reliable. Go Mono. But two solid sources are next best thing, not three and not five. Also those that introduce delays to 'balance' multiple sources at different distances are utterly fooled. This ruins any chance of a solid phantom image and disintegrates with even the smallest head movement.
I know this because I try it. Perhaps Griesenger's theories as to what actually happens are better than most because he has had a lot to do with creation side of music.
Research into popular preferences, polling is utterly irrelevant to me in a world of MP3, the audio of RAP, and Ed Sheeran.
When people hear something better, they go for it, e.g. the move from MP3 to Vinyl. Some day they will be enthralled to discover Digital Audio, and music including the fundamental notes.

 

[Matthew J Poes]

Griesinger fully supports multichannel music as necessary to accurately reproducing a musical performance. He fully believes in surround music. It seems that @DanDan you do not? I’m not sure you two agree here.

I believe it is a reality, a fact that a 2-channel speaker system cannot accurately reproduce spaciousness and ASW as defined. It’s impossible and I don’t see anything you present as countering that notion other than because you have vast experience and disagree.

in much of what You say I think we agree more than we disagree. You seem to argue that a properly set up mixing environment removes the distracting reflections allowing you to hear into the music more clearly. I agree that is how studios are setup. I disagree that is how it’s supposed to be. Or at least, I disagree if the goal is to reproduce something like a symphonic performance. If we have an actual standard to compare against, then there is no circle of confusion. Or no need for one. The problem comes when we start talking about typical studio recordings in which any added environment is contrived artificially. That isn’t a bad thing per say, but it does mean that we as consumers have no way of knowing what it is supposed to sound like.

I still disagree that headphones provide an immersive experience but maybe we just define those terms differently. My experience with headphones is that they provide a locked in your head imaging experience. I only find that not to be true when headphones are given a binaural recording or one that has been processed in a similar way.

you touch upon a point relevant to the thread starter, which is the appropriate balance for a system when reflections have been removed. Sadly I believe many of these folks do not understand human hearing or acoustics and fundamentally misunderstand what is desirable and why. They believe flat is best in a reflection free zone. That this equal neutral. That preference studies are just that. Not about accuracy but about preferences. Well...that isn’t accurate. And further, as I wrote about in an article on mics and ears, how FFT’s and omni mics record sound is fundamentally different from how our ears detect and process sound. Equating the two without accounting for these preference studies and psychoacoustics is a recipe for disaster, which is what you observed.

first we must understand how human hearing evolved. We know for a fact that the majority of listeners prefer a tonal balance that has elevated bass. The amount of elevated bass that is preferred varies, but it’s still fairly universal. We can only guess why, but that remains a fact that has held up over a ton of studies. We also know for a fact that if you take an instrument, say a cello, and you measure it in any room vs an anechoic chamber, that instrument will have more bass in the room. Why? Reflections of course. There is a greater accumulation of reflections at low frequencies in the integration zone.

more facts, we know over the centuries humans have spent most of their time inside structures. We know sound has accentuated bass inside these structures. So it makes sense that humans would be used to or prefer this elevated bass. The brain even may accommodate it.

more facts, we know that when you take a speaker and you measure it in a true anechoic chamber, then measure the same speaker in a normal domestic room, the bass is elevated due to reflections. We also know we hear that as elevated bass. The brain doesn’t filter it out. that point is important. The reason why is because the sound we perceive below the Schroeder frequency is essentially a reverberant field. There is no direct sound, it’s an equal mix of reflections. The brain can’t filter that out.

more facts, we know that the measurement technique commonly in use, be it an RTA or Sine Sweep will collect direct sound with a mix of reflections. It does this at all frequencies but the proportion of reflections that is in the measurement and impacts the steady state response increases as we go lower. This is because of the timing of those reflections.

we also know that the brain is a powerful acoustic filter. By measuring the ITD and IAD, the shift in tonal balance (HRTF), and the timing the brain can tell where sounds are coming from and filter out the noises it doesn’t want to pay attention to. In a room, that is reflections primarily. as I said earlier, it can’t do this at low frequencies, but it can do this at high frequencies. A microphone cannot Do that. Not in the same way the brain does. That means a steady state room response doesn’t match what the brain actually hears.

now comes the problem, where @DanDan and I have disagreed in the past. I don’t agree that a reflection free zone is truly possible. First, at low frequencies even anechoic chambers are not reflection free. They have a limit. This limit is far higher in studios. In my experience around 100-150hz. Then we have the midbass through highs. What I have witnessed in an IR from an anechoic chamber or outside is that there is absolutely nothing after the direct sound impulse. In the ETC you see a right triangle shape and then nothing at all. Just the fuzz from room noise or actually mic noise. In these RFZ studios, that isn’t what I see. I see reflections, but they are not pushed out past the integration zone. Or close to it. Ranging from a second peak at around 15ms to as much as 50ms. Maybe there are some that push it even further. I also usually see that the second reflection is far down in level. Often at least 10dB in poor quality studios and as much as 40dB in the best I ever measured.

now @DanDan if you have an impulse response of an RFZ that shows true anechoic behavior I would love to see it. But for the actual point I’m going to now make, it’s not important.

we know that the brain perceived neutral as having elevated bass in a room. We know that this is even true of outdoor events. The preferred tonal balance raises the bass. We know that measuring a system doesn’t properly equate to what the brain perceives and the correlation between in room measurements and perception are very low. That means the appropriate room curve SHOULD show a rise in the bass. That is a neutral response. Those engineers who shoot for a flat measured response in an RFZ are doing it wrong. There is no scientists or physicists that I’ve ever met who agree with their beliefs. It arises from nothing more than conjecture and it’s fundamentally wrong.

 

[DanDan]

I am glad you concur on the big issues.
"Those engineers who shoot for a flat measured response in an RFZ are doing it wrong." One, who many followers regard as the best in the world..... Thomas Jouanjean.
Of course a ZWER or truly Anechoic is utterly impossible. In Noise Measurement we omit anything -10dB from the data. In Control Rooms 20/20 has been a rule of thumb.
i.e. No reflections higher than -20dB during the first 20mS. Obviously Haas at play there.
Most of my work is remedial or relatively small, but I typically see nothing or not much above -25/30.
Most of my life's work both Recording and Live, has been with voices and acoustic instruments.
To be quite frank, I would conclude that a decent Grand Piano or Hall are rare birds, and miced up drum kits are much nicer than the real thing! LOL....

"Griesinger fully supports multichannel music as necessary to accurately reproducing a musical performance. He fully believes in surround music. It seems that @DanDan you do not? I’m not sure you two agree here."
Most music recordings are stereo. They can be faked surround by adding a 4.0 Reverb. But I find sampled spaces seem to work better than algorithmic, sorry Dave!

"I believe it is a reality, a fact that a 2-channel speaker system cannot accurately reproduce spaciousness and ASW as defined. It’s impossible and I don’t see anything you present as countering that notion other than because you have vast experience and disagree.

Reality doesn't require belief.

Try listening to this

 

[Matthew J Poes]

I am glad you concur on the big issues.
"Those engineers who shoot for a flat measured response in an RFZ are doing it wrong." One, who many followers regard as the best in the world..... Thomas Jouanjean.
Of course a ZWER or truly Anechoic is utterly impossible. In Noise Measurement we omit anything -10dB from the data. In Control Rooms 20/20 has been a rule of thumb.
i.e. No reflections higher than -20dB during the first 20mS. Obviously Haas at play there.
Most of my work is remedial or relatively small, but I typically see nothing or not much above -25/30.
Most of my life's work both Recording and Live, has been with voices and acoustic instruments.
To be quite frank, I would conclude that a decent Grand Piano or Hall are rare birds, and miced up drum kits are much nicer than the real thing! LOL....

"Griesinger fully supports multichannel music as necessary to accurately reproducing a musical performance. He fully believes in surround music. It seems that @DanDan you do not? I’m not sure you two agree here."
Most music recordings are stereo. They can be faked surround by adding a 4.0 Reverb. But I find sampled spaces seem to work better than algorithmic, sorry Dave!

"I believe it is a reality, a fact that a 2-channel speaker system cannot accurately reproduce spaciousness and ASW as defined. It’s impossible and I don’t see anything you present as countering that notion other than because you have vast experience and disagree.

Reality doesn't require belief.

Try listening to this

well but we seem to be disagreeing on facts. The definition of spaciousness is based on the ICCC measurement and that requires reflections in the room. The definition of ASW is based in lateral reflections. So it’s not a belief, it’s a fact. But yet we seem to disagree.

as for RFZ, what you note is exactly what I typically see. But then the folks doing this need to understand that just because the reflections in the first 20ms are down -20dB doesn’t mean their total energy isn’t changing the response as compared to anechoic. It is. And our ears still filter that out. The difference is that the degree to which it is contributing to a shift in the response has changed so applying something like theHarman curve might not apply.

accept that we still know the bass should be elevated. I had a whole conversation with Welti on this. He called it the messy middle. For the reasons I gave, we know the bass should be elevated in any environment. Anechoic or not. We also know the treble should fall off at ever higher frequencies. Say above about 5khz. The exact amount seems to vary somewhat.

but that messy middle. That area between around 300hz and 5khz is completely dependent on the rooms reflectiveness and speaker directivity. It may be desirable in an RFZ to have a flatter response here. That might be more neutral. It would depend on the degree to which the reflections are suppressed. It’s because the measurement is still being corrupted by the reflections relative to what the ear hears. Just not as much.

 

[DanDan]

I am a big aficiando of language. Forgive my ignorance but I have not not encountered or can't remember encountering definitions of Envelopment, Immersion, Spaciousness.
So it is difficult to know what you are referring to. In my world the terms envelopment describes the headphone experience well. Immersion is standing in the middle of the Orchestra, or listening on 5 Full range speakers.
Space as we use the word is an absence of conflict between individual sounds. We space them apart by electronically diminishing masking frequencies from one or the other, emphasising unique characteristics, panning, and distance via reverb. As Griesenger said, this is only within the recording.
-20 to -30dB clusters of reflections do not contribute audibly. Easily tested if you have a DAW and decent Reverbs at hand.
It may be interesting to share my experience of experimenting with 'The Target Curve'
I was Beta testing Dirac Live. I tried all sorts of variations of LF boost, HF roll off over a 2 year period.
My secondary monitoring is on two other systems in real domestic rooms. So I could keep checking for success at translation. Ultimately I ended up with the Bruel and Kjaer curve.
Which luckily also was the most pleasing to listen in.
Unexpectedly, shelving Eq, nor any form of straight line Eq didn't sound as good as actually curved curves.
Only one frequency is flat, 2Khz. This really only applies in effectively anechoic spaces.
In more lively ones, one might want to diminish the bass, electronically or perhaps by moving speakers away from the Front Wall.....LOL!

 

[Matthew J Poes]

I wondered if definitions were getting in the way. You come from the practice side, I come from the physics side. I use the terms as defined and used by acousticians and academics.

they are standardized terms with specific operational definitions.

examples of papers exploring this are:

(PDF) Apparent source width and listener envelopment in relation to source-listener distance

PDF | The perceptions of ASW and LEV at different source-listener distances in a reverberant soundfield were investigated subjectively and objectively.... | Find, read and cite all the research you need on ResearchGate

www.researchgate.net

The Psychoacoustics of Apparent Source Width, Spaciousness and En...: Ingenta Connect

www.ingentaconnect.com

Apparent source width:

Apparent source width - Wikipedia

en.m.wikipedia.org

And my brief definition is that it’s the phenomena we perceive as the space between instruments and the instruments space within the room.

spaciousness and envelopment have been determined to be the same thing but were used as different terms at onetime. It turns out that what people perceived as spaciousness and envelopment arise from the same source. Just different ways of describing those dimensions. I define it briefly as the sense of the space you are in. The sense of the room around you.

http://www.ecousticsystems.com/sites/default/files/library/objmeas.pdf

I credit David with having developed the objective measures of this but I may be incorrect.

Metrics - concerthalls.org

What do you notice about the sound quality when you are listening to a concert in your favorite hall? Is it clear, dry, intimate, warm, fuzzy, brilliant, loud? Acousticians have compiled a list of acoustic qualities that are considered to

www.concerthalls.org

This provides some common definitions.

https://www.davidpublisher.org/Public/uploads/Contribute/597ee905e8b25.pdf

Discussion of these concepts in the context of surround reproduction.

I’ve taken acoustical physics courses at three Univeristies now (including one in England) and I am currently working on my INCE board certification and they use the same terminology.

my understanding is that all of these concepts came out of research into concert hall acoustics. Basically large room acoustics. They don’t always translate to small rooms. In fact, the standards of good sound never do. You are familiar with this concept in the form of RT60 standards and predictions fitting small rooms poorly. There exists very little research examining these concepts in small rooms. For example, we know there is a correlation between measures of IACC and ASW and our perception of changed in spaciousness and source width. But we have no idea what a good target number would be. Those targets exist for large spaces.

 

[DanDan]

Good, thank you. I am glad to be the idiot sometimes. It's the only way to learn.
Concert Halls, I work Live quite a lot, and of course notice the exceptionally good. So rare unfortunately But here's a treat for the eyes, also probably the best I have heard.

Palau-de-la-Musica | Virtual tour generated by Panotour

Virtual tour generated by Panotour

www.tartinvillephoto.com

 

[Matthew J Poes]

Good, thank you. I am glad to be the idiot sometimes. It's the only way to learn.
Concert Halls, I work Live quite a lot, and of course notice the exceptionally good. So rare unfortunately But here's a treat for the eyes, also probably the best I have heard.

Palau-de-la-Musica | Virtual tour generated by Panotour

Virtual tour generated by Panotour

www.tartinvillephoto.com

you are far from an idiot. Who would know these terms and their definitions if they didn’t explicitly study them? Most people I know who know these terms have a PhD in acoustics.

one of the biggest challenges I face in my reviews and tech articles are explaining commonly used concepts in technical ways. Terms like space, imaging, bass, treble, warmth, timbre, neutral, dynamic, etc. are all commonly used and everyone has their own definition. I use the standardized operational definitions and try to make that clear. I’ve had problems where people argue with my definitions, even though they are standard.

I’m a stickler for operationalizing concepts before using them. It bugs me when people throw around catchy terms without a solid definition. I’m actually “inventing” a new research method known as rapid cycle evaluation. The concept comes from control theory like continuous quality improvement and the term was coined by someone else. But they didn’t define it and used it very loosely. I’m now writing a paper defining what it is, is not, what methods you use as part of it, etc.

 

[DanDan]

 

[Adhoc]

@ dirt9: I usually don’t like to give more than general proposals. -From measurements and experience in my own room I know that unknown / forgotten variables can make for quite a lot of difference, compared to plain theory. This could be the sofa, upholstered with fabric or leather (?), its placement in the room, dispersion pattern from the speakers, do they wave guides / horns with controlled directivity (?), crossover frequencies, how many subs and their placement versus massive room borders, wall construction etc, etc.

If you haven’t done it already, make a drawing of your room in Sketchup or on paper, scale 1:5 or so. Personally I find it quicker to check various ”solutions” on a paper drawing and move around bits of paper symbolizing the stuff in the room (also in the same scale).

In general; if you strive to attenuate the reflection from the nearby side wall down to -10 / -20 dB range use thick insulation beside the speaker up to and past the speaker’s mirror point on the nearby sidewall. The reflection from the speaker on the opposite sidewall will be further up towards the centre of the room. Here you can (probably) use a thinner absorbtion layer, as the that reflection will be higher in frequency due to (common) cone speaker directivity and a bit longer path length. With the scaled drawing, a protractor, speaker toe in and some knowledge of the speaker’s dispersion pattern, you can get an idea about how thick the insulation need to be on the opposite wall, -to save a bit on the room width. The absorbers you have drawn reminds me of those John H Brandt show on his page. You can improve on yours if you include some wave guides inside. Drawing: https://www.jhbrandt.net/wp-content/uploads/2018/05/1152-A Trap Section 6 Inch.pdf (John is an experienced designer so these are proven designs. There are also drawings on other thicknesses As you see from the absorbtion diagram even 6” thick doesn’t reach very low in frequency. α = 0,8 is equivalent to 7 dB attenuation, 0,5 = 3 dB ... )

 

[DanDan]

Another great post. If I might tweak a little though.....
Side and Ceiling Reflections are generally assumed to be Medium and High Frequency because of focus on these 'First Reflections'
As we often sit at half width and half height, I suggest full range absorption is very important above and to the sides. There are many designs for the DIY 100mm trap. Despite assertions about perforation adding more absorptive area, we have seen that a solid frame gains absorption from other losses. It would appear that there is no point in going to the trouble.
Also, it does appear that Polyester batts simply outperform other fibres. Given their appearance and physicality they do not need cosmetic covering nor framing.
Poly is appearing more and more, except it seems in the USA.

4 Pieces CARUSO-ISO-BOND® WLG035 100mm Broadband Absorber fleece

WLG 035 >= 10 000 Pa*s/m² 40kg /m³ Mid-Dense

www.don-audio.com

Also, the damped membrane effect of a medium to high density batt is often ignored by those following GFR predictions only. I believe there is a very useful boost in LF absorption available by using 703 /705 or similar, which can be further enhanced by bonding an actual thin membrane. e.g. FRK. http://ethanwiner.com/density.html