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An Enticing Marketing Story, Theory Without Measurement?

Floyd Toole

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At the risk of being accused of boosting sales on my recent book, all of this is covered in some detail, with measurements and references. BTW the book is not a "profit center" for me - it is a technical book.

The short story is that steady-state in-room measurements reveal nothing reliable about the performance of the loudspeaker, which is the essential starting point for understanding potential sound quality. It is essential to have comprehensive anechoic data on the loudspeaker in order to interpret room curves. If you have such anechoic data in the right format it is possible to predict the steady-state room curve above about 500 Hz in normally reflective rooms. It is also possible to calculate a prediction of subjective ratings in double-blind tests. If one has access to such data choosing a neutral sounding loudspeaker is easy. Without it, it is a crapshoot.

So, if one has a known neutral loudspeaker what does "room EQ" bring to the party? Above about 500 Hz, very little that is reliable - mostly general spectral trends; not detailed irregularities, for reasons mentioned in my last post. At low frequencies equalization is almost certainly beneficial and easily measured steady-state data are all that is necessary. The most important curve is the one measured where you are listening, not averaged over the room or multiple seat listening area. The latter obviously represents an average, not what is truly heard at any seat. It is popular because it makes curves look so much better. One can have an audience EQ and a personal EQ in some flexible systems.

A free measurement system like REW is excellent. The next step is to find prominent spectral peaks below about 500 Hz and attenuate them using a parametric equalizer, another relatively simple task if one has access to DSP in the signal path. Avoid filling narrow dips. They are not as audible as they are visible - humans respond readily to excessive sound at specific frequencies (resonances) but largely ignore narrow dips; an absence or deficiency in sound. The major commercial algorithms differ mainly in how they decide which peaks to attenuate and which dips to fill. Doing it manually allows one to decide by ear which actions are the most beneficial. Often only minor intervention is necessary.

When I see extremely flat and smooth high resolution full bandwidth room curves it is an indication that some things were done that probably should not have been done. :)

I have one of those all-singing-dancing-highly-advertised-elaborately-mathematical processors. It took manual intervention to restore the inherent excellence of my neutral loudspeakers after "room EQ". This is a work in progress. One definitely needs mathematics and DSP skills, but one also needs the acoustical and psychoacoustic knowledge to provide the necessary guidance and discipline. In some of the systems it is evident that the latter elements are deficient. The profit motive is obvious though. Note that most of the room EQ algorithms come from companies that do not make loudspeakers.
 
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watchnerd

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It's a lot more work than buying another toy but can't wait to start now to do something that will truly improve my listening....

+1 to this.

So much money people waste on things that don't actually move the sonic needle much, if at all, compared to dealing with having better room / speaker interactions and using better recordings.
 

watchnerd

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ove
When I see extremely flat and smooth high resolution full bandwidth room curves it is an indication that some things were done that probably should not have been done. :)

This seems to be a common internet phenomenon.....people going full EQ overkill even above 500Hz to hammer everything super flat, then sharing the graph online, getting praised for it, others copying it, etc.
 

DDF

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I have one of those all-singing-dancing-highly-advertised-elaborately-mathematical processors. It took manual intervention to restore the inherent excellence of my neutral loudspeakers after "room EQ". This is a work in progress.

I've read most of the literature on audibility of reflections. I think there is a great deal of promise in a constrained system that only corrects floor bounce, and only in the modal region. It would correct a main source of colouration without needing to try and (futility) dump power into the floor notch hole. I'd then like to see it extended to the wall behind the speaker, see what what it does and then at a stretch ("stretch" because direction is beginning to veer from the loudspeaker incidence), ceiling bounce. Again, all constrained to the modal region.

I think the state of the art in the science backs up the inherent promise of this application. I agree the sledgehammer approach that seems to be in vogue is about making pretty pictures that have nothing to do with improving sound accuracy.
 

watchnerd

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Note that most of the room EQ algorithms come from companies that do not make loudspeakers.

Given they make speakers (Paradigm, Martin Logan) and allegedly used the Canadian NRCC as part of the process, do you think the Anthem Room Correction has some advantages, then?
 
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Floyd Toole

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I've read most of the literature on audibility of reflections. I think there is a great deal of promise in a constrained system that only corrects floor bounce, and only in the modal region. It would correct a main source of colouration without needing to try and (futility) dump power into the floor notch hole. I'd then like to see it extended to the wall behind the speaker, see what what it does and then at a stretch ("stretch" because direction is beginning to veer from the loudspeaker incidence), ceiling bounce. Again, all constrained to the modal region.

I think the state of the art in the science backs up the inherent promise of this application. I agree the sledgehammer approach that seems to be in vogue is about making pretty pictures that have nothing to do with improving sound accuracy.
Look at Section 7.4.7 "Floor Reflections: a Special Case?". There is evidence that humans evolved with something always below their feet and when acoustical evidence of it is removed they may not approve. Human adaptation cannot be ignored. However, in the modal and adjacent boundary region (below about 500 Hz in domestic rooms) judicious EQ can be beneficial. Chapters 8 and 9 focus on this region.
 
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svart-hvitt

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At the risk of being accused of boosting sales on my recent book, all of this is covered in some detail, with measurements and references. BTW the book is not a "profit center" for me - it is a technical book.

The short story is that steady-state in-room measurements reveal nothing reliable about the performance of the loudspeaker, which is the essential starting point for understanding potential sound quality. It is essential to have comprehensive anechoic data on the loudspeaker in order to interpret room curves. If you have such anechoic data in the right format it is possible to predict the steady-state room curve above about 500 Hz in normally reflective rooms. It is also possible to calculate a prediction of subjective ratings in double-blind tests. If one has access to such data choosing a neutral sounding loudspeaker is easy. Without it, it is a crapshoot.

So, if one has a known neutral loudspeaker what does "room EQ" bring to the party? Above about 500 Hz, very little that is reliable - mostly general spectral trends; not detailed irregularities, for reasons mentioned in my last post. At low frequencies equalization is almost certainly beneficial and easily measured steady-state data are all that is necessary. The most important curve is the one measured where you are listening, not averaged over the room or multiple seat listening area. The latter obviously represents an average, not what is truly heard at any seat. It is popular because it makes curves look so much better. One can have an audience EQ and a personal EQ in some flexible systems.

A free measurement system like REW is excellent. The next step is to find prominent spectral peaks below about 500 Hz and attenuate them using a parametric equalizer, another relatively simple task if one has access to DSP in the signal path. Avoid filling narrow dips. They are not as audible as they are visible - humans respond readily to excessive sound at specific frequencies (resonances) but largely ignore narrow dips; an absence or deficiency in sound. The major commercial algorithms differ mainly in how they decide which peaks to attenuate and which dips to fill. Doing it manually allows one to decide by ear which actions are the most beneficial. Often only minor intervention is necessary.

When I see extremely flat and smooth high resolution full bandwidth room curves it is an indication that some things were done that probably should not have been done. :)

I have one of those all-singing-dancing-highly-advertised-elaborately-mathematical processors. It took manual intervention to restore the inherent excellence of my neutral loudspeakers after "room EQ". This is a work in progress. One definitely needs mathematics and DSP skills, but one also needs the acoustical and psychoacoustic knowledge to provide the necessary guidance and discipline. In some of the systems it is evident that the latter elements are deficient. The profit motive is obvious though. Note that most of the room EQ algorithms come from companies that do not make loudspeakers.

To better understand how the DRC experts think, I believe one has to take their mathematics and models seriously, assuming that the math is coherent and consistent, but asking about which ASSUMPTIONS the DRC crowd take to make and develop their models. If DRC is junk science, I think the easiest way to find out if the DRC emperor is naked, is to ask about which assumptions they make in their models and microphone measurements. Assumptions could be of different kinds, relating to physics (very classical view in audio), psychoacoustics (a newer part of audio science) and neurology (a more novel part of audio science).

«Show me your assumptions!» could be an interesting question to cast more light on how DRC modelers think.

But again: Good old blind tests would be evidence of the more robust kind because «generally speaking you can believe the observations and you don’t need to believe the theories».
 

Floyd Toole

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Given they make speakers (Paradigm, Martin Logan) and allegedly used the Canadian NRC as part of the process, do you think the Anthem Room Correction has some advantages, then?
The designers of the Anthem algorithm took part in the last NRCC experiments just after I left for sunny SoCal and all activities ended. They focused on low frequency room EQ and they appear to have avoided the worst problems. Many users take advantage of the option of EQing only at low frequencies.
 

Juhazi

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This seems to be a common internet phenomenon.....people going full EQ overkill even above 500Hz to hammer everything super flat, then sharing the graph online, getting praised for it, others copying it, etc.

Well Floyd said something like "...with regular speakers with typical DI". I have been playing with dipole diy multiway speakers for the last 6 years (so far) and this is one of the questions I still have. I have had impaired hearing since childhood, hard to hear anything above 6kHz in audiometry. But still, with my loudspeakers I do hear differencies up there.

In my AINOgradient 4-way dipoles with minidsp 4x10HD, first I had Fountek NeoCD3.5H as tweeter (xo 3kHz) and it sounded sort of excellent, but made faster decay at spot - actually it was too excellent! I added a rearside upwards tilted "ambience" tweeter that helped quite a lot and decay was smoother. Finally I bought a dipole B&G Neo3 PDR tweeter to accompany B&G Neo8 PDR. It sounds much mellower than horn+amb despite measurement at spot is pretty much equal (both first and decayed response). My room response is practically flat for a single speaker above Schröder and I don't use any high Q room corrections, just tonal balancing something like 2 octaves bw. Others say this sounds good too.

This is approximately what I listen to now. Notice the diffrerence between L/R at same spot! - I don't try to eq that either. Decay is up to 140ms.
ainogneo83 v7a LR decay response RT-tile.jpg
 
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DWPress

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Like it or not Dr. Toole, some of us will be getting the revised edition anyway. ;)

Thanks for your informed, thought provoking ideas you've freely shared here and elsewhere. As I said - I was ready to invest in hardware/software that would allow for FIR and processes like DIRAC but going to sit tight and focus on room issues instead. While I may revisit assisted EQ in the future it will be with a different view of what it might actually accomplish in the context of my space and not until after I have a firmer grasp of reflection/dispersion and absorbtion and its implementation.
 

RayDunzl

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Is a "swept sine" considered to be a "steady state" tone in FR measures?
 
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DDF

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Look at Section 7.4.7 "Floor Reflections: a Special Case?". There is evidence that humans evolved with something always below their feet and when acoustical evidence of it is removed they may not approve. Human adaptation cannot be ignored. However, in the modal and adjacent boundary region (below about 500 Hz in domestic rooms) judicious EQ can be beneficial. Chapters 8 and 9 focus on this region.

I agree this is self evident but it only applies to a sub set of use cases. Floor bounce is natural for a performer in a room. If its not captured in the recording already and the sound field presented is attempting to emulate listening to the performer in close proximity, then floor bounce is a valid inclusion on playback. Perhaps this is one more reason why the singer/guitar solo (close miced without a strong recording studio floor bounce) is so popular in audio demos, its reproducing an acoustic scene thats natural to the playback environment. In this case, your theory holds.

However its not natural for listening to many types of recordings. Floor bounce is largely non existant for symphonic music (orchestra level) or very different in nature (balcony). Same for chamber music or any music where the listener is far from the player (who may be elevated) and the time difference of the floor bounce from incident is small. In these cases (and its a significant use case set) human adaptation doesnt apply and floor bounce is an unwanted colouration. Its these use cases that I'm most interested in accurately reproducing and that the recording side is most typically diligent in not bastardizing for airplay to start with.
 

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However, because the direct and reflected sounds arrive from different directions, which the mic cannot recognize, it is ignoring the reality that two ears and a brain can recognize the difference. What looks like possible audible coloration is interpreted by humans as simple, innocuous spaciousness - a.k.a. a room. Humans have considerable abilities to separate the timbral identities of a sound source from those added by a room. It happens in all live, unamplified, music performances and all conversations.

We have no measurement apparatus that performs as a living binaural hearing system,
What about the special microphone used by Trinnov? It looks as if it has 4 channels and it should be possible to separate direct and reflected sound.
 

LTig

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At the risk of being accused of boosting sales on my recent book, all of this is covered in some detail, with measurements and references. BTW the book is not a "profit center" for me - it is a technical book
.
Too late, I already made the upgrade from edition 1 to 3.:)
 

Floyd Toole

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Perhaps the most persuasive evidence relating to the audible consequences of the floor bounce is in:
Silzle, A., Geyersberger, S. Brohasga, G., Weninger, D., and Leistner, M. (2009). “Vision and Technique behind the New Studios and Listening Rooms of the Fraunhofer IIS Audio Laboratory”, Audio Eng. Soc. 126thConvention, Preprint 7672.
It is said:
“Regarding the floor reflection, the audible influence by removing this with absorbers around the listener is negative—unnatural sounding. No normal room has an absorbent floor. The human brain seems to be used to this.”
Other anecdotal experiences appear to agree. Is it absolutely definitive? The Fraunhofer room is an impressive facility, so it comes down to what program they were listening to. I have not gone back to look.

As for floor bounces in symphony orchestras, there is a floor below the musicians so a floor bounce is included in the "direct" sound arriving at all listeners - different for different elevations, obviously. I recall reading about investigations into the audible consequence of this floor bounce, but have no references to offer. I sit in front balcony/terrace seats to avoid the acoustical interference of audience and the seat-dip effect, both of which add to the floor bounce in the main "orchestra" seats.

Chasing this issue to ground will require some real research. In the meantime, evidence that humans adapt to listening spaces is encouraging.
 

watchnerd

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If I'm going to do physical room treatments...not rebuilding any structures, but perhaps some diffuser panels or bass traps, if warranted....should I try to do room correction EQ first, then do it, or the other way around?
 
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