Listening Room Acoustics

A

admin

Audioholics Robot
Staff member
Unfortunately, where sound quality is concerned, the acoustics of the listening room is rarely taken into account. Indeed, most people opt for expensive, top of the range sound systems in an attempt to reach the best-possible sound quality. But they often ignore one essential thing: the acoustics of the listening room itself. As a sound system is used in an enclosed space ‘a listening room’, the acoustical conditions of that room will inevitably take control over the sound quality. This article focuses on the main acoustical problems of the listening room and how they can deteriorate the perceived sound.


Discuss "Listening Room Acoustics" here. Read the article.
 
Soundman

Soundman

Audioholic Field Marshall
Unfortunately, where sound quality is concerned, the acoustics of the listening room is rarely taken into account. Indeed, most people opt for expensive, top of the range sound systems in an attempt to reach the best-possible sound quality. But they often ignore one essential thing: the acoustics of the listening room itself. As a sound system is used in an enclosed space ‘a listening room’, the acoustical conditions of that room will inevitably take control over the sound quality. This article focuses on the main acoustical problems of the listening room and how they can deteriorate the perceived sound.


Discuss "Listening Room Acoustics" here. Read the article.
Good article! But I wish I could find a tool or information that covers odd shaped rooms. This tool will not work for this type of room: http://www.bobgolds.com/Mode/RoomModes.htm

The problem with these tools is they assume your length, width, and height are the same throughout the entire room. Therefore, it cannot calculate an odd-shaped room. :(
 
Savant

Savant

Audioholics Resident Acoustics Expert
From the article:
Michel Leduc said:
• Speaker positioning: according to ITU BS-775-2 recommendation
• Room frequency response: +- 3 dB, from 250 Hz to 2 kHz.
• Space between axial standing waves : > 5 Hz, < 20 Hz
• Rt60: 0,3 x (V/100 m3)^1/3 +- 50 ms from 200 Hz to 4 kHz, typically 200 to 400 ms.
• Background noise level : NC-15 or near 20 dBA
• Early reflections (0 to 15 ms): -10 dB or less relative to direct sound
Just some quick thoughts on these:
Speaker Positioning
Standards are sometimes not the best source for this. I would suggest Toole's book, Sound Reproduction, as a guide for this.

Room Frequency Response
The guideline provided is for a very narrow frequency range. The ±3 dB over four octaves will not guarantee a good sounding room. IMO, the actual room response should be specified in line with Toole's recommendations (see book reference above) and should cover the entire audible range, 20 to 20k. Smoothing should also be employed as appropriate. No room will give a ±3 dB within that range of frequencies (or within the entire audible range) if smoothing or averaging is not somehow employed.

Space Between Axial Modes
The 5 Hz < max. spacing < 20 Hz criterion will generally give good results. Whether it should be specified is another story. Good design goal; possibly limiting spec. A room can sound fine with a handful of axial modes that deviate from this criterion. An upper limit should also be defined. Above the fourth or fifth order axial mode, the spacing typically becomes less important due to increased modal density.

T60
Again, this should be a design goal, but not a specification. Just because a room has a low T60 does not guarantee it will have good sound. A better requirement might be to limit early decay only and/or specify a requirement for the relative level of early reflections. (See below.)

Background Noise Level
This is probably the most unrealistic specification. If NC-15 can be achieved, that's great. But it will be a costly requirement. Typical sound levels in unoccupied residential spaces (with all heating/cooling systems operating) are NC-20 to NC-30, which would be fine for many listening spaces. Also, verifying an NC-15 specification has been met will require a very good sound level meter (ANSI Type 1 or better).

Early Reflections
As I mentioned, this is probably a better requirement than, and something that can probably be used in lieu of, specifying T60. However, the -10 dB requirement may be a bit stringent. (Not to mention the fact that it should probably be frequency dependent.) It may have been close to state-of-the-art thinking when the referenced paper was written (1994), but we have learned a lot in the last 15 years. Much of it is contained within Toole's book, which I think I mentioned above. ;)

I may have more later...all I have time for now.
 
M

Michel Leduc

Enthusiast
From the article:

Just some quick thoughts on these:





Speaker Positioning
Standards are sometimes not the best source for this. I would suggest Toole's book, Sound Reproduction, as a guide for this.
Jeff,
Thank you for Toole's book reference. I will have the university buy this new book for us. For the moment, I prefer put my confidence in standards that are well known and widely accepted, made by a bunch of specialists.

Jeff, this is a 2 1/2 page article here. Of course, I am aware of what you are specifying and I agree to most of it. Given the space and time, I could have detailed much more. In my article, my first goal is to demonstrate that acoustics is under-appreciated. I had to give a summary of design guidelines and recommendations, so I chose the most important from the International Telecomunication Union and the European Broadcasting Union. For example, the tolerance limits for the operational room response specified by EBU is given from 50 Hz to 16 kHz. I just specified four octaves, where the curve is flat. In my article, which is an introduction, I want to show readers and enthusiasts that, acoustically speaking, they might be far away from what could be near the truth. (Is there a truth?)

I am sure if you read the article with this in mind, you will find it ok.

As for Dr Toole, I will explain my point of view later in this response.

Room Frequency Response
... Smoothing should also be employed as appropriate. No room will give a ±3 dB within that range of frequencies (or within the entire audible range) if smoothing or averaging is not somehow employed.
I don't feel I need to explain how to do acoustical measurements in this article. It is obvious that procedures affect data.

Space Between Axial Modes
The 5 Hz < max. spacing < 20 Hz criterion will generally give good results.
That's why I have stated Gilford's criterion, as a general rule.
A room can sound fine with a handful of axial modes that deviate from this criterion.
Of course, room modes don't manifest with the same amplitude at a given point.
An upper limit should also be defined. Above the fourth or fifth order axial mode, the spacing typically becomes less important due to increased modal density.
The Schroeder frequency (or around it) marks the superior limit from which modal density becomes high enough so there won’t be any coloration due to standing waves. (But the Schroeder frequency is being discussed by many.)


T60
Again, this should be a design goal, but not a specification. Just because a room has a low T60 does not guarantee it will have good sound. A better requirement might be to limit early decay only and/or specify a requirement for the relative level of early reflections. (See below.)
Yes, other parameters should be taken into account.
Background Noise Level
This is probably the most unrealistic specification. If NC-15 can be achieved, that's great. But it will be a costly requirement. Typical sound levels in unoccupied residential spaces (with all heating/cooling systems operating) are NC-20 to NC-30, which would be fine for many listening spaces.
I agree that the ITU recommendation is demanding here.
Also, verifying an NC-15 specification has been met will require a very good sound level meter (ANSI Type 1 or better).
This is not a problem; every acoustical consultant has a type 1 SLM.
Early Reflections
As I mentioned, this is probably a better requirement than, and something that can probably be used in lieu of, specifying T60.
We probably shouldn't use the term RT60 since, most of the time, there is no diffused reverberant field in small rooms.

However, the -10 dB requirement may be a bit stringent. (Not to mention the fact that it should probably be frequency dependent.)
I usually attain this objective as long as the first null frequency of the comb filter is absorbed.
It may have been close to state-of-the-art thinking when the referenced paper was written (1994), but we have learned a lot in the last 15 years. Much of it is contained within Toole's book, which I think I mentioned above. ;)
ITU recommendations (R-775) where revised in 2006.
As for Dr Toole... I get different results when I do his experiences with my 30 some students.
I may have more later...all I have time for now.
You are very welcome to add specifications, but let's work in team here.

Best Regards;

Michel Leduc
 
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F

fast1

Audioholic
you brought up a really good point, most people miss out the room, it plays such an impt role
 
Savant

Savant

Audioholics Resident Acoustics Expert
Michel,

First, I wanted to make clear that the intention of my post was not to be confrontational. I failed to mention - and should have right off the bat - that the article is a good introduction to the subject. Kudos! :)

Just a few thoughts on your reply:

The Schroeder frequency (or around it) marks the superior limit from which modal density becomes high enough so there won’t be any coloration due to standing waves. (But the Schroeder frequency is being discussed by many.)
Yes, it seems to me that the Schroeder frequency thing has been beaten to near-death in a number of threads... :confused:

It is worth noting that the Schroeder frequency was originally presented with a lower limit to room volume; I believe Schroeder's original reserach included V > 400 m³ as a criterion. In other words, it's a large room parameter. In small rooms, a room's "critical frequency" is often found to be lower, typically in the neighborhood of the "Davis" frequency, (from Sound System Engineering, by Davis & Davis):

fc = 3*c/Lmin

where,
fc = critical frequency
c = speed of sound in air
Lmin = smallest room dimension.

This is equivalent to the highest 6th order axial mode. (Also, a comment that accompanies this equation in the Davis text is "Do not view it as a rigid fixed frequency." ;) )


We probably shouldn't use the term RT60 since, most of the time, there is no diffused reverberant field in small rooms.
I couldn't agree more!!! :D

Thanks for the reply. Good stuff, Michel!
 
Savant

Savant

Audioholics Resident Acoustics Expert
Reread the article again and thought that there was one point left worth commenting on / clarifying:
Michel Leduc said:
Lateral reflections create phantom sources outside the speakers, enlarging the stereo image. By doing so, they also contribute to enlarge every sound element distributed between the speakers. The result is a blurred image that lacks precision.
Quite a few researchers have proven that this is not necessarily the case. Lateral reflections are not necessarily detrimental to sound quality. Toole demonstrates this repeatedly (and empirically) in his book. My own 2007 article on Audioholics proposes using the work of Yoichi Ando to deal with early (including lateral) reflections, the treatment for which may include reflective treatment as a viable option.

Of course, absorbing lateral reflections has a long history of "working." But, after reading Toole and researching the topic on my own, I have a feeling this may have evolved out of a necessity to address the historical inadequacies and shortcomings of the loudspeakers, and not necessarily because the room was doing something "bad." It must be kept in mind that the off-axis response of the loudspeakers has a LOT to do with the choice of treatments for the side walls of a listening room. Again, this is something Toole delves into quite a bit.

BTW, if it appears I'm playing the "broken record" with regards to the Toole book, I apologize. However, the book is well-deserving of the praise. IMO, it's a new de facto "bible" for small room acoustics.

Finally, please don't take any of this personally, Michel. :) As I mentioned above, much has been learned a lot about small room acoustics in last decade or two. In the spirit of working together and keeping Audioholics "cutting-edge," I feel it is important to bring different perspectives to this topic.
 
gene

gene

Audioholics Master Chief
Administrator
I have a copy of Dr. Tooles book at my bedside and in the process of reading it. Apparantly small room and big room acoustics are quite a different ball of wax and what applies to one usually doesn't apply to the other. It has alot to do with the critical distance and the transition region. Interestingly enough I have found that the inroom frequency response of a speaker above 300Hz (transition region) is fairly similar to that of the anechoic response at a couple of meters. Its below 300Hz where things get really nasty.
 
M

Michel Leduc

Enthusiast
Reread the article again and thought that there was one point left worth commenting on / clarifying:

Lateral reflections are not necessarily detrimental to sound quality. Toole demonstrates this repeatedly (and empirically) in his book.
I've repeated Toole's experiment on early reflections*.
As a teacher, I have the opportunity to do several experiences with my students during which we measure and evaluate the sound quality in an experimental listening room where we can change the acoustical treatment (removing, changing place, changing thicknesses, etc.) We got results prooving that early reflections are detrimental.

I think I can explain the differences between M. Toole’s experiments and mine. My students have all extensive experience in listening tests. They all have an acute sense of hearing that M. Toole’s participants may not have had. They are able to detect a 15 ms delay with a percussive sound, and also to note a change in the sound timbre, even with such a short sample. This is why M. Toole’s participants may not have reacted the same as our people. Though I do not deny M. Toole’s studies at all.

The question is: what are the listening skills of audiophiles?


* The Detection of Reflections in Typical Rooms, SEAN E. OLIVE AND FLOYD E. TOOLE

Michel Leduc
 
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avaserfi

avaserfi

Audioholic Ninja
I've repeated Tolle's experiment on early reflections*.
As a teacher, I have the opportunity to do several experiences with my students during which we measure and evaluate the sound quality in an experimental listening room where we can change the acoustical treatment (removing, changing place, changing thicknesses, etc.) We got results prooving that early reflections are detrimental.

I think I can explain the differences between M. Toole’s experiments and mine. My students have all extensive experience in listening tests. They all have an acute sense of hearing that M. Toole’s participants may not have had. They are able to detect a 15 ms delay with a percussive sound, and also to note a change in the sound timbre, even with such a short sample. This is why M. Toole’s participants may not have reacted the same as our people. Though I do not deny M. Toole’s studies at all.

The question is: what are the listening skills of audiophiles?


* The Detection of Reflections in Typical Rooms, SEAN E. OLIVE AND FLOYD E. TOOLE

Michel Leduc
What was the length between the original source and the reflection in your study? Ideally the time should be 5-10ms. 15ms could present issues as you seem to have noted.

A few other points:

1) I believe, often times Toole and Olive used trained listeners as well as audiophiles. The trained listeners participating within the studies would be considered very experienced at identifying such abnormalities.

2) I refer you to Differences in Performance and Preference of Trained vs Untrained Listeners in Speaker Tests. JAES. Vol. 51, No. 9 P. 806-825. This paper shows that the differences between trained and untrained listeners you suggest would not be a considerable factor given proper execution of the experiment.

3) The speakers used will play a factor in perception of performance. If the speakers were highly resonant sources it is likely the lateral reflections were poorly perceived due to the increased audibility of the resonance due to the reflection. See the following (please note the paper on resonance audibility also contains an in depth analysis of the subject and previous research):

Toole, Floyd E. Loudspeaker Measurements and Their Relationship to Listener Preference - Part 1. J. Audio Engineering Soc., Vol. 34, No. 4. 227 - 235 April 1986

Toole, Floyd E. Loudspeaker Measurements and Their Relationship to Listener Preference - Part 2 J. Audio Engineering Soc., Vol. 34, No. 5. 323 - 348 May 1986

Toole, Floyd E.; Olive, Sean E. The Modification of Timbre by Resonances: Perception and Measurement J. Audio Engineering Soc., Vol. 36, No. 3. 122 - 142 March 1988.
 
M

Michel Leduc

Enthusiast
Of course, I used the exact same setup as Toole did, to be able to compare the results.

In his 'early reflection' experiment, Toole mentions that he had only two trained listeners.
 
J

jostenmeat

Audioholic Spartan
What was the length between the original source and the reflection in your study? Ideally the time should be 5-10ms. 15ms could present issues as you seem to have noted.
They are able to detect a 15 ms delay with a percussive sound, and also to note a change in the sound timbre, even with such a short sample. This is why M. Toole’s participants may not have reacted the same as our people. Though I do not deny M. Toole’s studies at all.
avaserfi, could you kindly explain why the delay should be within 5-10 ms? And why 15ms presents issues? I was for a long time under the impression that the delay needed to be more than 6ms for us to even discern that it was a reflection to begin with. no.5 taught me, if I understood correctly, that the relative strength of the reflection must be considered along with the delay(?). I suppose there is a certain "strength" of the first reflection being assumed?

Sorry if I sound like an idiot... (but, after all, secondary reflections will be +15ms).

The question is: what are the listening skills of audiophiles?
A few other points:

1) I believe, often times Toole and Olive used trained listeners as well as audiophiles. The trained listeners participating within the studies would be considered very experienced at identifying such abnormalities.
What is the difference between a trained listener and an audiophile? I think* I would consider them to be the same.

FWIW, my close friend, amazing musician, cellist in my string quartet, who could recite harmonic progressions on cue, couldn't recognize clipping when he was cranking some music in the car.
 
Savant

Savant

Audioholics Resident Acoustics Expert
Michel,

Toole makes a clear distinction between trained and untrained listeners. Toole has noted the differences, as other researchers, such as yourself, have. Ando has even quantified those differences, at least in the case of musicians versus ordinary listeners.

To me, the box on pp. 119 of Sound Reproduction sums it up nicely. I will quote a portion of it, just to give a taste :) :
Floyd Toole said:
...it is entirely reasonable to think that acousticians who spend much of their lives moving around in rooms while listening to revealing test signals can become sensitized to aspects of sound fields that ordinary listeners blithely ignore. This is a caution to all of us who work in the field of audio and acoustics. Our preferences may reflect accumulated biases and therefore may not be the same as those of our customers.
(Emphasis is mine.) (I also noticed that I had penciled a note in the margin on pp. 119 that says, "Possibly the most important section in this book." :D )

It is our responsibility to understand the science of acoustics. However, understanding the science is only the first step. It is much more important to be able to use that scientific understanding to create a room that sounds good to the listener. Therein lies the art of acoustics.

I hope you don't mind—and I'm not trying to nitpick—but I'm going to use the background noise criteria you cited as an example:

What sense would there be to setting an NC-15 criteria for background noise for a listening room that will have, because of circumstances beyond the acoustician's control, an HVAC system that can only meet NC-25? Is it really responsible to dictate thousands of dollars worth of changes to the HVAC system when NC-25 is probably going to be perfectly acceptable for the listener? In the grand scheme of things, spending boatloads of money for what amounts to ~10 dB more S/N is probably a poor use of precious listening room funds. (IMHO it is anyway.) The listener is fully capable of enjoying the room whether they have 45 or 55 dB of S/N.

That's not to say that the listener with deep pockets shouldn't have the best possible room. I have designed listening rooms for those types of folks. Background noise barely measurable with my Type 1 instrumentation; "ruler-flat" frequency response down to 32 Hz; laboratory quality isolation; ultra-low T60; early reflections at least 15 dB down; etc. Those are certainly fun rooms to work on. To me, they sounded phenomenal and I consider them some of my best work.

However, for quite a few of those designs, I noticed that some of my colleagues—many of them ordinary listeners—would comment that it sounds good. No "WOW!" No blown away. Just "good." Like "what's-all-the-fuss-about?" good. To me, this is an important thing to keep in mind.

To put it another way, is the room going to be used by an audiophile that claims she can hear flies fart, or is it going to be used by a family of four to experience The Wizard of Oz on the "big screen" for the first time since giving up the 19" TV in the family room, or is it going to be used by someone who just enjoys listening to good Mozart recordings in stereo? I don't believe the widely varying design needs of these listening rooms (et al) can be addressed by standards. (But that's not to say we shouldn't try! :) :) :) )
 
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M

Michel Leduc

Enthusiast
Michel,

Toole makes a clear distinction between trained and untrained listeners. Toole has noted the differences, as other researchers, such as yourself, have. Ando has even quantified those differences, at least in the case of musicians versus ordinary listeners.

To me, the box on pp. 119 of Sound Reproduction sums it up nicely. I will quote a portion of it, just to give a taste :) :
(Emphasis is mine.) (I also noticed that I had penciled a note in the margin on pp. 119 that says, "Possibly the most important section in this book." :D )

It is our responsibility to understand the science of acoustics. However, understanding the science is only the first step. It is much more important to be able to use that scientific understanding to create a room that sounds good to the listener. Therein lies the art of acoustics.

I hope you don't mind—and I'm not trying to nitpick—but I'm going to use the background noise criteria you cited as an example:

What sense would there be to setting an NC-15 criteria for background noise for a listening room that will have, because of circumstances beyond the acoustician's control, an HVAC system that can only meet NC-25? Is it really responsible to dictate thousands of dollars worth of changes to the HVAC system when NC-25 is probably going to be perfectly acceptable for the listener? In the grand scheme of things, spending boatloads of money for what amounts to ~10 dB more S/N is probably a poor use of precious listening room funds. (IMHO it is anyway.) The listener is fully capable of enjoying the room whether they have 45 or 55 dB of S/N.

That's not to say that the listener with deep pockets shouldn't have the best possible room. I have designed listening rooms for those types of folks. Background noise barely measurable with my Type 1 instrumentation; "ruler-flat" frequency response down to 32 Hz; laboratory quality isolation; ultra-low T60; early reflections at least 15 dB down; etc. Those are certainly fun rooms to work on. To me, they sounded phenomenal and I consider them some of my best work.

However, for quite a few of those designs, I noticed that some of my colleagues—many of them ordinary listeners—would comment that it sounds good. No "WOW!" No blown away. Just "good." Like "what's-all-the-fuss-about?" good. To me, this is an important thing to keep in mind.

To put it another way, is the room going to be used by an audiophile that claims she can hear flies fart, or is it going to be used by a family of four to experience The Wizard of Oz on the "big screen" for the first time since giving up the 19" TV in the family room, or is it going to be used by someone who just enjoys listening to good Mozart recordings in stereo? I don't believe the widely varying design needs of these listening rooms (et al) can be addressed by standards. (But that's not to say we shouldn't try! :) :) :) )
I will read Toole's book as soon as the university get's it. I may discover how come I got different results with the reflections experiment.

Yes, like I've said, ITU's recommendation of NC-15 is demanding.

Michel Leduc
 
mtrycrafts

mtrycrafts

Audioholic Slumlord
What is the difference between a trained listener and an audiophile? I think* I would consider them to be the same.

....
Can be but not necessarily. I have no real insight what training they go through but I suspect they get special controlled training and maybe extensive, what the different aberrations sounds like from small amounts to ones that are objectionable: frequency aberrations, distortions, phases, reverb, most everything you can think of.
Trained listeners perform better, more accurately, quickly and repeatable results compared to non trained, yet, both have same or very similar preferences for the music reproduction putting the notion to rest that we all hear different:D
 
M

Michel Leduc

Enthusiast
I refer you to Differences in Performance and Preference of Trained vs Untrained Listeners in Speaker Tests. JAES. Vol. 51, No. 9 P. 806-825. This paper shows that the differences between trained and untrained listeners you suggest would not be a considerable factor given proper execution of the experiment.
Andrew,

I went trough this paper (rapidly) yesterday. It is very interesting indeed. It made me rethink. I concluded the following...
This study has been conducted to find out if trained listeners were necessary to identify what is (or should be) the best speaker, in term of preference. It shows that trained and untrained listeners come to the same preference. But I see that there sense of hearing varies. I keep in mind the following (from the conclusion);

Different groups of listeners use different parts of the preference scale. Trained listeners use the lowest part of the preference scale, indicating they may be more critical and harder to please.

The average FL values of the trained listeners were 3–27 times higher than those measured by the other groups.


So when it comes to detect the sound of short delays and the localization etc... (like in Toole's reflection experiment) I still wonder if hearing skills could affect the test results. If we think about the Haas effect of around 35 ms, it's an average value for average listeners. But it is true that trained listeners can detect a delay as short as 15 ms (monophonic) with percussive sound (my experiments) ... just to state that they have more listening skills.

This reading was interesting but I am still not convinced that Toole's conclusions in the reflection experiment can not be, at least, discussed.

Michel
 
mtrycrafts

mtrycrafts

Audioholic Slumlord
.

The average FL values of the trained listeners were 3–27 times higher than those measured by the other groups.[/I]

So when it comes to detect the sound of short delays and the localization etc... (like in Toole's reflection experiment) I still wonder if hearing skills could affect the test results. If we think about the Haas effect of around 35 ms, it's an average value for average listeners. But it is true that trained listeners can detect a delay as short as 15 ms (monophonic) with percussive sound (my experiments) ... just to state that they have more listening skills.

This reading was interesting but I am still not convinced that Toole's conclusions in the reflection experiment can not be, at least, discussed.

Michel
But, what happens when you don't have monophonic signals but rather 2, 3 or 5 sources of info coming at you? Have you experimented with time delay and perhaps multi point source of info? Did you use percussive instruments as a test signal or some other signals? Perhaps as the signal gets more complex and simultaneously competes with other sound, that delay may be much higher?
 
tonmeister

tonmeister

Audioholic
I've repeated Toole's experiment on early reflections*.
As a teacher, I have the opportunity to do several experiences with my students during which we measure and evaluate the sound quality in an experimental listening room where we can change the acoustical treatment (removing, changing place, changing thicknesses, etc.) We got results prooving that early reflections are detrimental.

I think I can explain the differences between M. Toole’s experiments and mine. My students have all extensive experience in listening tests. They all have an acute sense of hearing that M. Toole’s participants may not have had. They are able to detect a 15 ms delay with a percussive sound, and also to note a change in the sound timbre, even with such a short sample. This is why M. Toole’s participants may not have reacted the same as our people. Though I do not deny M. Toole’s studies at all.

The question is: what are the listening skills of audiophiles?


* The Detection of Reflections in Typical Rooms, SEAN E. OLIVE AND FLOYD E. TOOLE

Michel Leduc
I would be interested in reading the results of your study. Our reflection detection study used trained subjects as well. I was one of them and I am a trained musician, Tonmeister (McGill University) and a formally trained listener with audiometric normal hearing. It's entirely possible that your training regiment produces listeners more sensitive to reflections - but our results were pretty well in agreement with previous studies.

A lot of the differences could be related to differences in other variables in your study such as the program signals, method used, questions asked,etc.

We also have an experimental room (see my current blog posting "seanolive.blogspot.com) where we can change the acoustical treatment and capture, store,reproduce and measure the perceptual differences using binaural room scanning methods. This way, the different acoustical room treatments can A/B'd instantaneously -- producing a very sensitive method for hearing differences, although not necessarily ecologically valid since listeners seem to adapt to room acoustics in a few seconds.

Cheers
Sean Olive
Director of Acoustic Research
Harman International
 
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