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

[Bjorn]

Wow, you really like to take things out of context. First, "small room" was not a given in the paper and your criticism is out of context.

I was simply pointing out the paper contained errors. I think that's worth mentioning.

Then, of course, one can create a moderately diffuse tail in a smallish (not tiny) room with a lot of work (that isn't worth it for a couple of obvious reasons) but it's probably better not to have much of a tail (like I said, I'm not at all fond of LEDE), and finally, a T60 is absolutely measurable in such places unless they are too noisy, even though they are unlikely to be long, pleasant, or useful. Of course, I'd probably use T20 in most such places, but you already knew that, didn't you? Your claim to "doesn't apply" is simply evidence you don't know how to apply it as far as I'm concerned. I certainly labor under no such difficulties.

This is exactly why I don't want to get involved into this discussions. Here you again bring in wrong understanding of fundamentals related to small room acoustics which takes it down another bunny trail. Most of what you describe above is highly based on misunderstandings.

 

[j_j]

I was simply pointing out the paper contained errors. I think that's worth mentioning.

This is exactly why I don't want to get involved into this discussions. Here you again bring in wrong understanding of fundamentals related to small room acoustics which takes it down another bunny trail. Most of what you describe above is highly based on misunderstandings.

Oh, spare me. There's more than one way to go about this. There is no universal solution. I can easily measure what you claim is a misunderstanding. I can trivially get useful information from that kind of measurements. There's nothing incorrect about this, and there are no misunderstandings involved.

 

[Bjorn]

Oh, spare me. There's more than one way to go about this. There is no universal solution.

Quite the contrary, some things are definitive (and which is the case here) and based on evidence. If you want an in depth explanation and willing to learn and be corrected, you can find the information and references about this in communities of small room expertise. It would take hours only to explain part of this here.

 

[j_j]

Quite the contrary, some things are definitive (and which is the case here) and based on evidence. If you want an in depth explanation and willing to learn and be corrected, you can find the information about this in communities of small room expertise.

Your arrogance is almost amusing, I'll give you that. Did it every occur to you that some folks besides you have some expertise, and may disagree rather substantially with some of the arguments going back to Sabine and Schroeder, and maybe even argued with Manfred about some of that?

Did it ever occur to you that stationarity of measurements is a key issue here? Yes? No?

 

[tw99]

Quite the contrary, some things are definitive (and which is the case here) and based on evidence. If you want an in depth explanation and willing to learn and be corrected, you can find the information and references about this in communities of small room expertise. It would take hours only to explain part of this here.

j_j is the guy with "Technical Expert" on his profile, and for good reasons.... so I think I'd take the opinion of someone with actual industry level contributions and awards above yours !

 

[fredoamigo]

it's a pity that this debate turned into an ego dispute with acoustic experts because it was very interesting.

 

[BDWoody]

j_j is the guy with "Technical Expert" on his profile, and for good reasons.... so I think I'd take the opinion of someone with actual industry level contributions and awards above yours !

He also has the 'Audio Luminary' designation, with good reason. If you aren't familiar with his contributions to the field, do yourself a favor and look him up...

I'd not want to be on the other side of a half-informed challenge to his credibility...

 

[j_j]

it's a pity that this debate turned into an ego dispute with acoustic experts because it was very interesting.

With all due respect, the opponent here has gone zero for two, in a way indicating book knowledge but rather missing the signal processing and physics of the situation, but keeps on playing semantics. More importantly, refusing completely to address the perceptual aspects, other than by citing an old paper that seems "mostly harmless" and reasonable but kind of misses the point.

It's impossible to have a discussion when one side simply casts aspersions, shifts ground every comment, and refuses to actually enter dialog, rather just plays semantics. That teaches no one anything except annoyance, and does not help the OP at all. Isn't that the goal, get the guy in the OP an answer?

 

[DonH56]

https://www.ieee.org/about/awards/bios/flanagan-recipients.html#2006---james-d.-johnston

I suspect JJ has done one or two things since 2006 but I lost count...

p.s. The last time I posted this some wise guy said something like "Oh, he's a digital audio guy, huh?" A bit of research will reveal the depth of understanding required and the breadth of the research performed and papers published...

At least I know without a doubt that I am the smartest guy on my keyboard. So long as I don't share it with anyone else.

 

[j_j]

Speaking of which, I think I got the original poster started on a decent path given his actual listening preferences.

 

[fredoamigo]

This paper here will shed more light on the subject?
AES E-Library » The Practical Effects of Lateral Energy in Critical Listening Environments

 

[j_j]

This paper here will shed more light on the subject?
AES E-Library » The Practical Effects of Lateral Energy in Critical Listening Environments

It's worth a look if you can get to the E-Library. I just read it. It's an interesting take that calls for a formal loudness (as opposed to level) analysis.

 

[amirm]

Two concrete examples of misunderstandings in the paper is the information about "diffuse tail" and "RT60". The first isn't used correctly related to small room acoustics. The other isn't relevant to small acoustics at all.

The misunderstanding is yours I am afraid. This comes up so much in online arguments that I wrote a complete article on it a while back: https://www.audiosciencereview.com/...large-small-rooms-a-matter-of-statistics.569/

What "invalidates" RT60 is the modal response which small rooms have so the impact is only in low frequencies as I show in the above article. So as JJ correctly stated, you can use T20 or any other approximation and be fine.

This is why we have targets of 0.2 to 0.5 for "RT60" for our listening spaces. If RT60 had no value, we could not make such suggestions.

 

[j_j]

What "invalidates" RT60 is the modal response which small rooms have so the impact is only in low frequencies as I show in the above article. So as JJ correctly stated, you can use T20 or any other approximation and be fine.

And, of course, T60 can be measured as a curve across frequency, and the modal responses will just fall where they may, and be painfully obvious.

The whole point of T60 as a function of frequency is not so unusual as some apparently think.

 

[Bjorn]

For those of you have an interest, you can read a short write up about reverberation time here:
https://www.lydogakustikk.no/sma-rom-og-etterklangstid/

If true reverberation time existed in small rooms, that would imply that thin absorption would work very well. It would imply that two types of very different random placement of treatment and without treating specifically specular reflections should both yield pretty much the same and good result. Anyone who has experience with various acoustic treatment, know however that this isn't the case.

And as side note but also examplifiies how specular reflections effects the sound in a small room is how a speaker with almost the same uniform directivity but different directivty index sounds very different in a small room. There may be no better example here than B&O Beolab 50 or 90; where you can change the directivity from 120° to 180° by a pressing a button and experience how completely different they sound. An RTx measurement of the speaker in the room would tell they measure very much the same.

 

[j_j]

If true reverberation time existed in small rooms,

If one can measure it, it exists. I can measure it, as a function of frequency, even. Q.E.D. Such a thing therefore exists. Therefore, your imagination is wrong. Furthermore thin absorbers do not work, therefore your paradigm is mistaken. Q.E.D.

Are you possibly not realizing that reverberation time is a function of frequency?

 

[March Audio]

For those of you have an interest, you can read a short write up about reverberation time here:
https://www.lydogakustikk.no/sma-rom-og-etterklangstid/

If true reverberation time existed in small rooms, that would imply that thin absorption would work very well. It would imply that two types of very different random placement of treatment and without treating specifically specular reflections should both yield pretty much the same and good result. Anyone who has experience with various acoustic treatment, know however that this isn't the case.

And as side note but also examplifiies how specular reflections effects the sound in a small room is how a speaker with almost the same uniform directivity but different directivty index sounds very different in a small room. There may be no better example here than B&O Beolab 50 or 90; where you can change the directivity from 120° to 180° by a pressing a button and experience how completely different they sound. An RTx measurement of the speaker in the room would tell they measure very much the same.

I'm afraid your pedantry ends up being hoist by your own petard.

You say

for true reverberation to exist, there needs to be a homogeneous and isotropic sound field. Usually such conditions are approached in physically large rooms that do not contain much absorption.

So what rooms, even large ones, are truly reverberant? Even you say it's only "approached".

So in reality considering the "decay" of sound in a room as somehow contradictory or inaccurate is not the case. This is what the "T(x)" data provides.

Modal data is trivial to separate.

 

[Bjorn]

My "pedantry" in the area is actually the belief the community of small room acoustics and was established decades ago. There hasn't been a discussion about it there since Theodore Schultz writings where he proved this. However, a lot of people are still unaware of the matter and the preconditions, thus we have ended up with a myth and misunderstanding.

Small rooms that are treated according to RTx measurements end up most of the time becoming encredible poor and needs to be fixed later. Something many small room acousticans have experienced.

As mentioned in the link:
"a large room for wide range music with a low frequency limit of 30 Hz is = to or >7079 m³ (250,000 ft³)".
“Spaces that qualify as “large rooms” can effectively utilize the myriad of equations based on the original assumptions of Sabine for his reverberation equations." In spaces exceeding these volumes and with an RT60 of 1.6 seconds or greater, we will find mixing homogenous sound fields of sufficient density to allow accurate engineering estimates of the level of each.”

Even in many large rooms one needs to be careful of not relying too much on RTx. It's known that calculation of reverberation time in large spaces has errors of something like 20-30%.

 

[fredoamigo]

Since I don't have access to this very recent RT study, can anyone here tell me if it's of interest? Well, I'd pay to see it.

https://asa.scitation.org/doi/abs/10.1121/1.5135582

 

[March Audio]

As mentioned in the link:
"a large room for wide range music with a low frequency limit of 30 Hz is = to or >7079 m³ (250,000 ft³)".
“Spaces that qualify as “large rooms” can effectively utilize the myriad of equations based on the original assumptions of Sabine for his reverberation equations." In spaces exceeding these volumes and with an RT60 of 1.6 seconds or greater, we will find mixing homogenous sound fields of sufficient density to allow accurate engineering estimates of the level of each.”

Even in many large rooms one needs to be careful of not relying too much on RTx. It's known that calculation of reverberation time in large spaces has errors of something like 20-30%.

Rt is a function of frequency. Even REW shows Rt V F, but granted to just use a single frequency number would be misleading for basing treatment choices. Modal data is trivial to separate.