• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). Come here to have fun, be ready to be teased and not take online life too seriously. We now measure and review equipment for free! Click here for details.

Diffusing 1st reflections of speakers that measure great on and off-axis - instead of absorbing

Joined
Jul 6, 2020
Messages
47
Likes
24
This is a fractal diffuser a gent in a Facebook forum used...thought it a good candidate 4’ behind an open baffle. Multiple units side by side hung on wall at different distances lowers the effective
69069CC1-68E8-413C-963F-A21AB994855D.png
frequency. The fellow used these both behind and on ceiling in front of his open
 
Joined
Jul 23, 2020
Messages
19
Likes
18
re pleasing" or "down-sloping off-axis is preferred"? Similarly, I think it's critical to understand the context of the individual listener's preferences, their musical context, and taking that into consideration when one states they "like" or "did not like" specific attributes like clarity, timbre, or reverbation/broadness/loudness.
it's not in my purview to understand the context of individual listener's preferences.

my statement was simply to communicate that it is critical to understand the nature and real-world behavior of the acoustical treatments when subjective preferences are provided. it's the erroneous assumption that all "diffusion is diffusion is diffusion" and that any/all "diffusers" function/behave/perceived the same - so when someone states "i tried diffusion at sidewalls and did/did-not like it", you need to drill down and understand/identify what exactly they are referring to when they say "diffusion" as different devices will behave wildly different.

you can't use the term globally as if all "diffusers" function the same. a poly will behave (thus sound) different than an RPG, than a BAD, etc. you also need to understand the bandwidth the device is relevant to and thus how it modifies the indirect specular energy that impedes the listening position over time.

i've also witnessed the same careless statements with LEDE rooms, where so many on audio forums appear to assume a "LEDE room" is any room that has a Live rear wall and Dead front wall - without actually understanding the precise time-domain requirements that must be met for a room to be considered "LEDE". this then muddies the water and confuses things as people think they have been in a LEDE room and state their opinion of it without realizing they actually haven't been in or constructed a LEDE room.

you'll on occasion find "studio designers" who insist they are designing LEDE rooms but can't even state the requirements or even know the appropriate tool to measure/verify the time-domain response. there is defintely a "telephone game" going on with the terms and why they have become so muddied-down over the years and thus why it is so paramount to understand the context involved. a "Circle of Confusion", if you will.
 
Last edited:
Joined
Jul 23, 2020
Messages
19
Likes
18
And I'm not a supporter of LEDE. That's both a question of physics and perception. That's also where an absolutist separation of "small" vs. "large" falls flat on its face.
what are your concerns with LEDE in terms of stereo reproduction?
 
Joined
Apr 21, 2019
Messages
64
Likes
86
my statement was simply to communicate that it is critical to understand the nature and real-world behavior of the acoustical treatments when subjective preferences are provided. it's the erroneous assumption that all "diffusion is diffusion is diffusion" and that any/all "diffusers" function/behave/perceived the same - so when someone states "i tried diffusion at sidewalls and did/did-not like it", you need to drill down and understand/identify what exactly they are referring to when they say "diffusion" as different devices will behave wildly different.

you can't use the term globally as if all "diffusers" function the same. a poly will behave (thus sound) different than an RPG, than a BAD, etc. you also need to understand the bandwidth the device is relevant to and thus how it modifies the indirect specular energy that impedes the listening position over time.
I wrote "I think this is why RPG seemed to prefer the term "diffusor" to indicate products that diffuse in both space and phase, as well as why they have often included information on scattering versus diffusion (as well as absorption) for their products."

If this wasn't clear, I meant that some products "diffuse" only in space but not phase (so-called polys, and in fact, they are hemicylinders unless placed in a collection), others have varying performance in space and phase, and virtually all also end up absorbing. RPG has often provided relatively frequency-specific information for scattering, diffusion, and absorption for their products. To make things worse, one's understanding of the performance of a specific device may be limited by the availability of only random incidence performance data, which is not the same as performance from a specific angle, nor its performance in a collection or array (i.e. polys when there are multiples). Even in the case of an absorber, only limited information is available for specific incidents and fabric coverings.

I suspect that the reality of the matter is that one's understanding of the performance of any specific device is actually quite limited, much more than a statement like "you..need to understand" might suggest.

Anyway, I doubt I have to say anything further of interest to you.
 
Joined
Jul 23, 2020
Messages
19
Likes
18
If this wasn't clear, I meant that some products "diffuse" only in space but not phase (so-called polys, and in fact, they are hemicylinders unless placed in a collection), others have varying performance in space and phase, and virtually all also end up absorbing. RPG has often provided relatively frequency-specific information for scattering, diffusion, and absorption for their products. To make things worse, one's understanding of the performance of a specific device may be limited by the availability of only random incidence performance data, which is not the same as performance from a specific angle, nor its performance in a collection or array (i.e. polys when there are multiples). Even in the case of an absorber, only limited information is available for specific incidents and fabric coverings.
concur 100%; the difficultly in identifying such "performance data" is simply the nature of the subject matter and inherent issues of using test room data/measurements being applied into another environment (and how few are even aware of those differences, as we all-too-commonly see reverberation chamber method data being applied to small room acoustics that lack a statistically random-incidence reverberant sound-field and where specific angle-of-incidence can be determined/applied). although it's apparent RPG has certainly taken much greater steps to determine product performance than those in the past - especially via the work of D'Antonio and Trevor Cox.

I suspect that the reality of the matter is that one's understanding of the performance of any specific device is actually quite limited, much more than a statement like "you..need to understand" might suggest.

Anyway, I doubt I have to say anything further of interest to you.
interesting tone. how exactly does the lack of data you indicate above seemingly disregard my statement that it is critical to understand the nature of the real-world behavior of the devices deployed when one is providing their subjective preferences on said room modifications?
 
Last edited:
Joined
Jul 23, 2020
Messages
19
Likes
18
Having been involved in a couple of LEDE builds with Chip Davis a long time ago, he explained it to me as a tool to be used by recording engineers to hear any comb filtering in the studio before the control room acoustics had its way with the sound. As one of those recording engineers, I can remember it worked very well. The "translation" was amazing, which is what is all about when recording, mixing and mastering on the music production side.

His whitepaper and subsequent certification of LEDE rooms is an interesting read and much more than just room treatments. While not my cup of tea for a regular listening room, (I prefer more live than dead, and not split between front and back), I did appreciate it for the tool it was. Amazing what one could hear from the recording studio that sounded like being right in the same room when listening through the monitors in the LEDE room. It was uncanny.
interesting paper and historical context from Syn Aud Con. i'm very-much-interested to hear how the user above is able to substantiate his claim that this is not science or "not an ounce of research using controlled listening" regarding this control room acoustical model or that these represent "schemes cooked up":

Remember, there is not an ounce of research using controlled listening to back the claimed benefits of RFZ and all the similar control room schemes cooked up in 1960s and 1970s.
could anyone shed light on how control room models such as LEDE/RFZ and the acoustical benefits they provide are somehow a "scheme"?
 
Joined
Apr 21, 2019
Messages
64
Likes
86
concur 100%; the difficultly in identifying such "performance data" is simply the nature of the subject matter and inherent issues of using test room data/measurements being applied into another environment (and how few are even aware of those differences, as we all-too-commonly see reverberation chamber method data being applied to small room acoustics that lack a statistically random-incidence reverberant sound-field and where specific angle-of-incidence can be determined/applied). although it's apparent RPG has certainly taken much greater steps to determine product performance than those in the past - especially via the work of D'Antonio and Trevor Cox.
I've skimmed "Acoustics of Small Rooms" by Mendel Kleiner and Jiri Tichy. Do you have any opinion on this book or them?

interesting tone. how exactly does the lack of data you indicate above seemingly disregard my statement that it is critical to understand the nature of the real-world behavior of the devices deployed when one is providing their subjective preferences on said room modifications?
What I mean is that I think it's probably exceedingly difficult for most of us to understand the real-world performance in specific applications. For example, I found the data that D'Antonio provided to Toole in his first/second edition of Sound Reproduction regarding normal and 45 degree incidence absorption data for fiberglass absorbers with and without Guilford of Maine FR701 covering to be eye-opening. How many of us are able to do such measurements in order to "understand...the real-world behavior"? Furthermore, even this does not allow me to understand what happens at 30 or 60 degrees, different fabrics like GoM Anchorage (likely much more reflective, so would this end up behaving somewhat more like a BAD panel in reducing higher frequency absorption?), eCose vs fiberglass, different densities of fiberglass, air gap behind the fiberglass, etc. Personally, I would say that it's important to have at least some basic understanding of the type of devices under use, while acknowledging that real-world data is limited and real-world performance may vary from manufacturers' claims.

Young-Ho
 

tuga

Major Contributor
Forum Donor
Joined
Feb 5, 2020
Messages
1,853
Likes
1,367
Location
Oxford, England
could anyone shed light on how control room models such as LEDE/RFZ and the acoustical benefits they provide are somehow a "scheme"?
To be fair I believe that "scheme" in that case was used as a synonym of "design" or "layout".
 
Joined
Jul 23, 2020
Messages
19
Likes
18
To be fair I believe that "scheme" in that case was used as a synonym of "design" or "layout".
it would be nice to have clarification, as that was not my interpretation. by inferring context from earlier in the comment, he states "not an ounce of research using controlled listening to back the claimed benefits of RFZ...", implying devious or dubious or doubtful. so i think "scheme" in this case implies a negative connotation, not simply "design" or "layout".
 
Joined
Apr 21, 2019
Messages
64
Likes
86
Harman uses Skylines several places as you see below.

When testing (blind) speakers they remove the side wall treatment so they experience the full effect of the horizontal off-axis response of the speakers.

Harman's white paper of the room reveals a lack of understanding smalll room acoustics and much is based on RTxx measurements. There are no relevant measurements. And as you see they use polys, which we know don't really diffuse the sound but focuses certain frequencies at certain angles. And the absorptive panels they use are thin (2"/5 cm probably) and offer now broadband treatment. The general treatment is also spread out a lot without any clear goal of treating specular reflections. The rear wall is quite dead and I would say opposite of preferred psychoacoustics when you have this distance.
I assumed the Skylines were meant to reduce slap echo with less absorption than an absorptive panel.

I know you're looking at the diagram, but when I look at the pictures, it's not clear to me what the depth of the absorptive panels are. Toole has argued against absorption of 2" or less in depth.

It looks like the room is meant to support multichannel listening. Can you comment on the preferred psychoacoustics in that setting?

The in-room loudspeaker response showed reassuring consistency between 7 channels, despite your concerns.

Just so you know, the only blind testing in this room would probably be for in-wall or on-wall speakers, since they show the mechanism for switching these sorts of speakers but not the floor shuffler. For other speakers, the MLL would probably be used, in case that affects your speculation about how this room would affect blind tests of bookshelf and floorstanding speakers.

Young-Ho
 
Joined
Jul 23, 2020
Messages
19
Likes
18
Toole has argued against absorption of 2" or less in depth.
granted this is not "Toole's argument" per se - it's a collective agreement and understanding in the acoustics and studio community known for decades that thin porous absorbers are not broadband to fully attenuate an indirect specular reflection and thus should not be utilized in such applications. although it is fantastic to see it communicated in such a fashion as Toole's work will certainly provide better "trickle-down" knowledge effect to the general audio/home community (as we still far-too-often see erroneous over-application of thin porous absorbers in home reproduction setups).

treatments need to be broadband in nature such that they are not simply modifying the spectral content of the reflection (ie, coloring, filtering, eq'ing, etc).

It looks like the room is meant to support multichannel listening. Can you comment on the preferred psychoacoustics in that setting? The in-room loudspeaker response showed reassuring consistency between 7 channels, despite your concerns.
you would presume Harman being Harman would provide ETCs of the multi-channel reproduction room for objective data on how the indirect energy arrivals for each active source impede the listening position over time (generated separately for EACH loudspeaker). has this data been published? it would be beneficial to understand why certain treatments are placed at certain positions, and the data pre/post of subsequent application of absorbers/diffusers. why were these locations chosen and for those specific treatments?
 
Joined
Apr 21, 2019
Messages
64
Likes
86
granted this is not "Toole's argument" per se - it's a collective agreement and understanding in the acoustics and studio community known for decades that thin porous absorbers are not broadband to fully attenuate an indirect specular reflection and thus should not be utilized in such applications. although it is fantastic to see it communicated in such a fashion as Toole's work will certainly provide better "trickle-down" knowledge effect to the general audio/home community (as we still far-too-often see erroneous over-application of thin porous absorbers in home reproduction setups).
Yes, I meant that I would be surprised if they were 2" absorbers since the treatments otherwise seem to follow his suggestions in his book.

[QUOTE}
you would presume Harman being Harman would provide ETCs of the multi-channel reproduction room for objective data on how the indirect energy arrivals for each active source impede the listening position over time (generated separately for EACH loudspeaker). has this data been published? it would be beneficial to understand why certain treatments are placed at certain positions, and the data pre/post of subsequent application of absorbers/diffusers. why were these locations chosen and for those specific treatments?[/QUOTE]

The summary slide in fact says "high quality multichannel playback over 6 listening seats." Since you were so critical about the "lack of understanding small room acoustics" and "opposite of preferred psychoacoustics," I was hoping that you would discuss the preferred psychoacoustics for multichannel playback in a small room. My limited understanding had been more absorption than desirable for stereo-only listening was fine, since the surround speakers would provide ambiance cues.

[edit: I was hoping Bjorn could discuss the preferred the psychoacoustics]

The listening treatments seem to largely follow suggestions laid out in Toole's book. He had briefly discussed Ando and Kishinaga in the context of IACC when recommending absorption for the front wall in stereo listening, also the lack of contribution of rear wall reflections (particularly from the center channel) in terms of perception of spaciousness when recommending absorption or diffusion in central portion of rear wall. He also suggests that opposite wall reflections for side surrounds are likely to contribute beneficially to the sense of space, so recommends "reflecting or scattering surfaces on walls opposite side-surround loudspeakers to enhance envelopment. Be careful about flutter echoes between the side walls."

It's nice to fantasize about measurements and experiments that Harman could do. I would not presume that Harman would provide anything just because someone on the Internet thinks it would be benficial.

Young-Ho
 
Joined
Jul 23, 2020
Messages
19
Likes
18
It's nice to fantasize about measurements and experiments that Harman could do. I would not presume that Harman would provide anything just because someone on the Internet thinks it would be benficial.
that is stunningly-absurd statement to imply such data is merely at the behest of "someone on the internet" and not something that would be collectively agreed to be relevant.

it's fascinating that a company that is so adamant about objective measurements of loudspeakers and proper "science" in terms of subjective performance listening tests then suddenly expects to do so in a room without providing measurements of the actual time-domain response at the listening position for each of the active sources? or at least detailed reasons why W treatment is placed in X location for Y active source at Z listening position?

at least to say: "here is proof that there are no high-gain, early/later-arriving signals impeding the listening position that may be detrimental to localization, imaging, etc"

ie, requirements for a room used to do such subjective tests needs objective measurements provided to verify that the room can be deemed (in-effect) "neutral" - and not imposing any destructive signals that may modify the subjective perception of the direct signal of the device under test.

fascinating that you insinuate that this is seemingly not relevant data, given the nature of the tests being performed in such rooms.
 
Joined
Apr 21, 2019
Messages
64
Likes
86
that is stunningly-absurd statement to imply such data is merely at the behest of "someone on the internet" and not something that would be collectively agreed to be relevant.

it's fascinating that a company that is so adamant about objective measurements of loudspeakers and proper "science" in terms of subjective performance listening tests then suddenly expects to do so in a room without providing measurements of the actual time-domain response at the listening position for each of the active sources? or at least detailed reasons why W treatment is placed in X location for Y active source at Z listening position?

at least to say: "here is proof that there are no high-gain, early/later-arriving signals impeding the listening position that may be detrimental to localization, imaging, etc"

ie, requirements for a room used to do such subjective tests needs objective measurements provided to verify that the room can be deemed (in-effect) "neutral" - and not imposing any destructive signals that may modify the subjective perception of the direct signal of the device under test.

fascinating that you insinuate that this is seemingly not relevant data, given the nature of the tests being performed in such rooms.
Ah, I think you're the one that JJ called a troll. I can see why. I will not respond further. I should have stopped at "Anyway, I doubt I have to say anything further of interest to you."
 

Duke

Active Member
Manufacturer
Forum Donor
Joined
Apr 22, 2016
Messages
218
Likes
359
Location
Princeton, Texas
Localhost128 bold-quotes youngho:

"I would not presume that Harman would provide anything just because someone on the Internet thinks it would be beneficial."

And replies:

that is stunningly-absurd statement to imply such data is merely at the behest of "someone on the internet" and not something that would be collectively agreed to be relevant.
And imo that's a stunningly absurd amount of offense to take at youngho's words.

I gather from the rest of your post that you feel entitled to a great deal more information than Harman provided. Couldn't you have said that without attacking youngho?
 
Last edited:
Joined
Jul 23, 2020
Messages
19
Likes
18
Ah, I think you're the one that JJ called a troll. I can see why. I will not respond further. I should have stopped at "Anyway, I doubt I have to say anything further of interest to you."
edit: apoligies - misread that as you insisting i was the one that called j_j a troll.

simply put, Harman is/was doing "science-based" subjective listening tests in a bounded acoustical space, of which data nor direct reasons have been publically provided (to my knowledge), objectively verifying that the room is deemed "neutral" for such tests - for verification.

why is this deemed acceptable when so many other "biases" are required to be addressed. a simple explanation of why certain treatments were chosen and subsequently placed (with respect to the myriad of active sources) - and objective measurements to verify that the room was deemed "neutral". it's still a sticking-point for me anytime these subjective listening tests come up: the test environment needs to be verified to be neutral and not imposing any high-gain, destructive indirect signals that could be detrimental to the perception of localization, imaging, etc.

do you disagree? should controlled-listening tests in the name of science be done-so in a bounded acoustical space of which the observers are not provided data of the actual indirect energy arrivals and how the placed "treatment" affects those wavelets?
 
Last edited:
Joined
Jul 23, 2020
Messages
19
Likes
18
And imo that's a stunningly absurd amount of offense to take at youngho's words.
i'm not sure where the "offense" was implied to be taken - could you elaborate?

finding it "absurd" that the request of such data for controlled, "science-based" listening tests are not provided as part of the overall report is only at the behest of an internet user, vs collectively understanding that it should be expected as part of the science and objective data/verification.

do you not question why harman placed those types of treatments in those positions with respect to the active sources for the tests? do you not wish to see objective measurements at the listening position that the room is not imposing any destructive signals that may alter the perception of the device under test - especially when the test scenario is subjective listening preferences? ie, "here is data to prove the room is not overly imposing on the perception of the loudspeaker under test".
 

Duke

Active Member
Manufacturer
Forum Donor
Joined
Apr 22, 2016
Messages
218
Likes
359
Location
Princeton, Texas
i'm not sure where the "offense" was implied to be taken - could you elaborate?
You called youngho's statement "stunningly absurd". That is a verbal attack, and in my opinion one which is uncalled for.

do you not question why harman... [whatever].
Can you not question why Harman did or didn't do whatever without attacking youngho?
 
Joined
Jul 23, 2020
Messages
19
Likes
18
You called youngho's statement "stunningly absurd". That is a verbal attack, and in my opinion one which is uncalled for.
thanks for elaborating - there was no "offense taken" at his statement as you originally implied, but i do fully concur now that you present it as a form of verbal attack on user youngho. concur and apologize. surely you will also call him out for implying i called "j_j" a troll earlier, when that was proven to be a lie? that too was a form of direct attack.


Can you not question why Harman did or didn't do whatever without attacking youngho?
in my subsequent re-statements, i have not attacked him beyond the orignal reply. is that not satisfactory? can anyone present a valid response to the questions regarding the validity of the test environment? or is the general consensus that verification of the room characteristics is not relevant for such science-based listening tests?
 

Duke

Active Member
Manufacturer
Forum Donor
Joined
Apr 22, 2016
Messages
218
Likes
359
Location
Princeton, Texas
thanks for elaborating - there was no "offense taken" at his statement as you originally implied, but i do fully concur now that you present it as a form of verbal attack on user youngho. concur and apologize.
Wow, sounds like it was a mis-understanding. I apologize for my assumption that you intended a verbal attack on youngho, and for confronting you about it with guns blazing instead of asking for clarification.

And I tip verbal hat to you for asking for clarification instead of returning fire.

surely you will also call him out for implying i called "j_j" a troll earlier, when that was proven to be a lie? that too was a form of direct attack.
But he didn't. I think you mis-read what he said:

Ah, I think you're the one that JJ called a troll.
He's saying that JJ called you a troll.

I don't know the back-story there, maybe it was also a mis-understanding.
 
Last edited:
Top Bottom