Burn-in: Real Or Imagined??? - Page 16 - AVS Forum
Forum Jump: 
Reply
 
Thread Tools
post #451 of 665 Old 01-14-2009, 11:21 AM
AVS Club Gold
 
Dennis Erskine's Avatar
 
Join Date: Jul 1999
Location: Near an airport
Posts: 9,143
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 17 Post(s)
Liked: 46
We may have the makings for a recording company here.

Dennis Erskine CFI, CFII, MEI
Architectural Acoustics
Subject Matter Expert
Certified Home Theater Designer
CEDIA Board of Directors
www.erskine-group.com
www.CinemaForte.net
Dennis Erskine is offline  
Sponsored Links
Advertisement
 
post #452 of 665 Old 01-14-2009, 12:13 PM
AVS Special Member
 
AndreYew's Avatar
 
Join Date: Jan 2000
Location: Southern California
Posts: 1,670
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by gedlee View Post

What is meant by "decorrelated to 40 Hz."? Do you mean down to 40 Hz or 40 Hz and down?

Down to 40 Hz, because it appears that it doesn't matter for frequencies below that.

Quote:


What small rooms lack at LFs is decorrelation. Large rooms have this by virtue of the multiple modes (high modal density). Small rooms only have a few modes and the signals thus tend to be highy correlated.

While that is true, the artificial method (referred to as the Hilbert of the bass by JJ, and shipping in an actual product in Lexicon's surround processors as Bass Enhance) seeks to simulate the perceptual cues we get from bass frequencies by maximizing the ITD fluctuations in that frequency range through a constant interchannel phase shift for the bass. That method depends on sparse room modes and the listener sitting in an area where the velocity is high and zero-crossing. David Griesinger has a paper on his website that explains this in more detail:

http://www.davidgriesinger.com/asa05.pdf

Its goal is to externalize bass signals. I think it works well, but it can sound funny on a lot of material (especially pop music which has no real-world reference) if you're used to mono bass, and it's obviously room-dependent. It works especially well on recordings of real acoustic events like bass drums in a concert hall.

I suspect that Griesinger was the protagonist in the Harman internal experiments on this subject.

--Andre
AndreYew is offline  
post #453 of 665 Old 01-14-2009, 12:21 PM
AVS Special Member
 
AndreYew's Avatar
 
Join Date: Jan 2000
Location: Southern California
Posts: 1,670
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by Dennis Erskine View Post

I visited a studio using Jensen Triacs mounted in kleenex boxes!

Muji sells little iPod speakers whose enclosures are cardboard. It's kind of cool --- they come flat, and you stand them up when you take them out of their package, like one of those pop-up picture books. They sound pretty bad, but at least they're cheap.

--Andre
AndreYew is offline  
post #454 of 665 Old 01-14-2009, 12:34 PM
Senior Member
 
gedlee's Avatar
 
Join Date: Dec 2008
Posts: 350
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 13 Post(s)
Liked: 37
Quote:
Originally Posted by AndreYew View Post

While that is true, the artificial method (referred to as the Hilbert of the bass by JJ, and shipping in an actual product in Lexicon's surround processors as Bass Enhance) seeks to simulate the perceptual cues we get from bass frequencies by maximizing the ITD fluctuations in that frequency range through a constant interchannel phase shift for the bass.

--Andre

It seems to me that the Hilbert method will not actually decorrelate the signals in the sense that the signals at the sources are uncorrelated. It may improve the ITD fluctuations, but mathematically speaking this is not necessarily a low spatial signal correlation. A true decorrelation filter requires more than just a Hilbert Transform changing the signals phase.

Earl R. Geddes
GedLee
gedlee is offline  
post #455 of 665 Old 01-14-2009, 12:38 PM
AVS Special Member
 
AndreYew's Avatar
 
Join Date: Jan 2000
Location: Southern California
Posts: 1,670
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by gedlee View Post

It seems to me that the Hilbert method will not actually decorrelate the signals in the sense that the signals at the sources are uncorrelated. It may improve the ITD fluctuations, but mathematically speaking this is not necessarily a low spatial signal correlation. A true decorrelation filter requires more than just a Hilbert Transform changing the signals phase.

Yes, that is right --- the phase shift method does not seek to decorrelate bass. It sets up room conditions so that the room modes assist in reproducing the kind of conditions that decorrelated bass would cause. All that and more are explained in the Griesinger paper I linked to.

--Andre
AndreYew is offline  
post #456 of 665 Old 01-14-2009, 12:47 PM
AVS Special Member
 
QueueCumber's Avatar
 
Join Date: Sep 2005
Location: Farmer McGregor's Garden
Posts: 6,089
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 14
Quote:
Originally Posted by gedlee View Post

PS. Anybody know why I don't get notification on any posts? Its checked in my profile.

You have to have mad riffs like Geddy Lee...

"It is worse still to be ignorant of your ignorance."
-- Saint Jerome (374 AD - 419 AD)

My Home Theatre
QueueCumber is offline  
post #457 of 665 Old 01-14-2009, 12:54 PM
AVS Special Member
 
Randybes's Avatar
 
Join Date: May 2002
Location: Midwest
Posts: 2,622
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 12
Quote:
Originally Posted by AndreYew View Post

Yes, that is right --- the phase shift method does not seek to decorrelate bass. It sets up room conditions so that the room modes assist in reproducing the kind of conditions that decorrelated bass would cause. All that and more are explained in the Griesinger paper I linked to.

--Andre

Since the subject is bass, I will put in a brief advertisement for Earl's room. I visited Earl in December and had the pleasure of listening to his home theater. The sound was superb and the bass integration with the main speakers was the best I have heard. I took the HAA Level 2 course, and I think we did a pretty good job with integration, but Earl's beat ours all to heck.
Randybes is offline  
post #458 of 665 Old 01-14-2009, 01:09 PM
AVS Club Gold
 
Dennis Erskine's Avatar
 
Join Date: Jul 1999
Location: Near an airport
Posts: 9,143
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 17 Post(s)
Liked: 46
...Randy, not to take away from Earl, but you guys started out with a Hotel Room to calibrate and had one day to do it (final cal). Give yourself some credit.

Dennis Erskine CFI, CFII, MEI
Architectural Acoustics
Subject Matter Expert
Certified Home Theater Designer
CEDIA Board of Directors
www.erskine-group.com
www.CinemaForte.net
Dennis Erskine is offline  
post #459 of 665 Old 01-14-2009, 01:16 PM
AVS Special Member
 
Randybes's Avatar
 
Join Date: May 2002
Location: Midwest
Posts: 2,622
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 12
Quote:
Originally Posted by Dennis Erskine View Post

...Randy, not to take away from Earl, but you guys started out with a Hotel Room to calibrate and had one day to do it (final cal). Give yourself some credit.

Well, you are right. I will say that anyone involved in the business or even a serious hobbyist will learn alot from the sessions. I loved it and had a great time as well.
Randybes is offline  
post #460 of 665 Old 01-14-2009, 02:48 PM
Senior Member
 
gedlee's Avatar
 
Join Date: Dec 2008
Posts: 350
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 13 Post(s)
Liked: 37
Randy

Thanks for the compliment.

PPS. I post once and I get one notification - is that how it works? You get notified only once for each post? Seems strange.

Earl R. Geddes
GedLee
gedlee is offline  
post #461 of 665 Old 01-14-2009, 02:53 PM
AVS Special Member
 
Randybes's Avatar
 
Join Date: May 2002
Location: Midwest
Posts: 2,622
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 12
Quote:
Originally Posted by gedlee View Post

Randy

Thanks for the compliment.

PPS. I post once and I get one notification - is that how it works? You get notified only once for each post? Seems strange.

At the top of this thread is thread tools, where you can subscribe to this thead. Not sure if that is what you did or not.
Randybes is offline  
post #462 of 665 Old 01-14-2009, 03:19 PM
Senior Member
 
gedlee's Avatar
 
Join Date: Dec 2008
Posts: 350
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 13 Post(s)
Liked: 37
It only says - unsubscribe - but I still only get a notice when I actually post something. Nothing in between.

Earl R. Geddes
GedLee
gedlee is offline  
post #463 of 665 Old 01-14-2009, 03:21 PM
AVS Special Member
 
Randybes's Avatar
 
Join Date: May 2002
Location: Midwest
Posts: 2,622
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 12
Weird. I will subcribe and see what happens.

Ok, I just got a notification by email that JJ_0001 repsonded so I am not sure what is up with the notification problem, Earl. When I subscribed, the default was no email that I had to change.
Randybes is offline  
post #464 of 665 Old 01-14-2009, 03:57 PM
Advanced Member
 
jj_0001's Avatar
 
Join Date: Sep 2006
Location: In the rain
Posts: 761
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 59 Post(s)
Liked: 40
Quote:
Originally Posted by gedlee View Post

It seems to me that the Hilbert method will not actually decorrelate the signals in the sense that the signals at the sources are uncorrelated. It may improve the ITD fluctuations, but mathematically speaking this is not necessarily a low spatial signal correlation. A true decorrelation filter requires more than just a Hilbert Transform changing the signals phase.

Very, very true.

I fear I can't actually speak more to methods at present. This is not because I don't have one, naturally.

James D. (jj) Johnston
jj_0001 is online now  
post #465 of 665 Old 01-15-2009, 03:33 PM
Member
 
cap'n's Avatar
 
Join Date: Jan 2009
Location: Los Angeles
Posts: 50
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Liked: 12
ok, my 4 cents (adjusted for inflation):

I believe low frequency signals in a room are normally fairly correlated at the ears - I mean left/right ear cross correlation at low frequencies. Bill Martens, who has done a lot of real research in this area has found it to be true as have I. Just to check, I just now loaded a recent measurement (random noise burst from multiple subwoofers measured at blocked ear canal of a dummy head) in our reference room, low pass filtered it at 80 Hz and plotted the left right ears. Very similar, correlation coefficient has to be near one.

I also did some research to try to demonstrate spatial bass (I call it "Bassiousness"). I went to great lengths to make the test sensitive to the effect I was studying. I used some program material that did have decorrelation at low frequencies. I even went so far as to find material that had simultaneous high signal levels and decorrelation (if you look closely at different programs, often the decorrelation comes at times when there is insignificant signal level). I also included as one of my programs the same contrived warble tone signals that Dave Greisinger uses in his demos. I used trained listeners, with a pretraining period (subwoofer only so they could hear any effects). I used the very sensitive 3 alternative forced choice test and double blind of course.

Several subwoofers configurations were tested, from a single sub at front/center to "stereo" subs at +/- 90 degrees, using either "stereo" or "mono" presentation of the bass, and listeners tried to detect the difference. Also, the responses for the difference configuraitons were pre-equalized to be flat (to remove that as a cue).

After statistical analysis, I found that listeners could only detect the difference between front/center mono and left/right stereo bass presentation (the two most dissimilar configuraitons), and that just barely, and under the most favorable conditions. And keep in mind we did not ask if they preferred one configuraiton over the other, just whether they could hear a difference. In the real world, you really need a contrived or otherwise unusual signal to hear it.

-------------
Todd Welti
Research Acoustician
Harman International Industries
cap'n is offline  
post #466 of 665 Old 01-15-2009, 03:43 PM
AVS Special Member
 
Dizzman's Avatar
 
Join Date: Mar 2001
Location: Bay Area
Posts: 5,251
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 12
lets get back to the OP question...

DO cables and speakers burn in?

(giggle)

I say no. but our perception/preference of then shapes over time.

Proud Daddy to Anastasia and Christopher.
Born October 26 2005.

Ob was the delivery doc.

Since i cannot rant on a soapbox in the town square...
http://commonsensehasdied.blogspot.com/
Dizzman is offline  
post #467 of 665 Old 01-15-2009, 03:52 PM
Advanced Member
 
jj_0001's Avatar
 
Join Date: Sep 2006
Location: In the rain
Posts: 761
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 59 Post(s)
Liked: 40
Quote:
Originally Posted by cap'n View Post

ok, my 4 cents (adjusted for inflation):

I believe low frequency signals in a room are normally fairly correlated at the ears - I mean left/right ear cross correlation at low frequencies. Bill Martens, who has done a lot of real research in this area has found it to be true as have I. Just to check, I just now loaded a recent measurement (random noise burst from multiple subwoofers measured at blocked ear canal of a dummy head) in our reference room, low pass filtered it at 80 Hz and plotted the left right ears. Very similar, correlation coefficient has to be near one.

I also did some research to try to demonstrate spatial bass (I call it "Bassiousness"). I went to great lengths to make the test sensitive to the effect I was studying. I used some program material that did have decorrelation at low frequencies. I even went so far as to find material that had simultaneous high signal levels and decorrelation (if you look closely at different programs, often the decorrelation comes at times when there is insignificant signal level). I also included as one of my programs the same contrived warble tone signals that Dave Greisinger uses in his demos. I used trained listeners, with a pretraining period (subwoofer only so they could hear any effects). I used the very sensitive 3 alternative forced choice test and double blind of course.

Several subwoofers configurations were tested, from a single sub at front/center to "stereo" subs at +/- 90 degrees, using either "stereo" or "mono" presentation of the bass, and listeners tried to detect the difference. Also, the responses for the difference configuraitons were pre-equalized to be flat (to remove that as a cue).

After statistical analysis, I found that listeners could only detect the difference between front/center mono and left/right stereo bass presentation (the two most dissimilar configuraitons), and that just barely, and under the most favorable conditions. And keep in mind we did not ask if they preferred one configuraiton over the other, just whether they could hear a difference. In the real world, you really need a contrived or otherwise unusual signal to hear it.

Ok, now go measure this result in a large venue. Your measurement results are expected for a small venue.

Your results with a dummy head (was it attached to a body?) seem to be lacking in the "interfering with the velocity field" factor, as well.

As to your test, you say 'equalized to be flat'. In what sense? Pressure at given points, energy at given points, volume velocity at given points? What points?

James D. (jj) Johnston
jj_0001 is online now  
post #468 of 665 Old 01-15-2009, 03:53 PM
Advanced Member
 
jj_0001's Avatar
 
Join Date: Sep 2006
Location: In the rain
Posts: 761
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 59 Post(s)
Liked: 40
Quote:
Originally Posted by cap'n View Post

In the real world, you really need a contrived or otherwise unusual signal to hear it.

I must challenge this statement.

In what way is a recorded signal from an existing concert-hall venue "contrived or "otherwise unusual"?

James D. (jj) Johnston
jj_0001 is online now  
post #469 of 665 Old 01-15-2009, 04:26 PM
AVS Special Member
 
Speedskater's Avatar
 
Join Date: Mar 2004
Location: Cleveland, Ohio
Posts: 2,040
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 14 Post(s)
Liked: 20
Quote:
Originally Posted by Dennis Erskine View Post

We may have the makings for a recording company here.

Using the Soundstream was an interesting task. Keeping a log of how much time was still available on the reel versus how long the next recording segment would be, so that you could rewind (a slow process) during an orchestra break to use the next 2 tracks. It used an 8 track instrumentation recorder, 2 tracks at a time. Oh, remembering that during cold weather, to touch the frame before touching any switches, because it used 74lsxxx digital logic and static electricity could feed through and do the unexpected. First time I used it they said "Kevin, don't make any mistakes this is costing $200 a minute!"

Kevin
Speedskater is offline  
post #470 of 665 Old 01-15-2009, 05:20 PM
AVS Special Member
 
QueueCumber's Avatar
 
Join Date: Sep 2005
Location: Farmer McGregor's Garden
Posts: 6,089
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 14
Can someone quantify at what volume a space is a large venue and no longer a small venue?

"It is worse still to be ignorant of your ignorance."
-- Saint Jerome (374 AD - 419 AD)

My Home Theatre
QueueCumber is offline  
post #471 of 665 Old 01-15-2009, 06:59 PM
Member
 
cap'n's Avatar
 
Join Date: Jan 2009
Location: Los Angeles
Posts: 50
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Liked: 12
Quote:
Originally Posted by jj_0001 View Post

Ok, now go measure this result in a large venue. Your measurement results are expected for a small venue.

Your results with a dummy head (was it attached to a body?) seem to be lacking in the "interfering with the velocity field" factor, as well.

As to your test, you say 'equalized to be flat'. In what sense? Pressure at given points, energy at given points, volume velocity at given points? What points?

I dont have any large venue measurements handy, so can't say. Our dummy is anatomically correct in almost every way which includes full torso. I dont understand your repeated mention of volume velocity. Our ears are pressure sensing organs. Are you implying that the impedance of the measurement microphone as compared to the eardrum should be accounted for? I'm not sure what "interfering with the velocity field" means.

Transfer functions (dB, omni measurement mic) of the different subwoofer configurations to a single mic located between the subjects ears (with the subject absent!) were equalized as flat as we could reasonably get.
cap'n is offline  
post #472 of 665 Old 01-15-2009, 07:12 PM
Member
 
cap'n's Avatar
 
Join Date: Jan 2009
Location: Los Angeles
Posts: 50
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Liked: 12
Quote:
Originally Posted by jj_0001 View Post

I must challenge this statement.

In what way is a recorded signal from an existing concert-hall venue "contrived or "otherwise unusual"?

I'm just saying that my research and experience suggests that if you played back the typical concert hall recording on, for example, a full range stereo playback system and compared it to a bass managed system (as for example if you mono the bass and play it back over the two speaker in the same positions and eq it to remove any resulting spectral differences) the difference would be very subtle. That is why Dave uses the decorrelated bass warble tones in his demos (and even they dont always work). I had to use contrived and/or unusual program material to even have a chance of detecting a difference. Of course if you are applying further processing (hilbert, decorrelated reverb, or whatever) that could certainly produce and audible effect - no argument there.

______________
Todd Welti
Research Acoustician
Harman International
cap'n is offline  
post #473 of 665 Old 01-15-2009, 07:20 PM
Advanced Member
 
jj_0001's Avatar
 
Join Date: Sep 2006
Location: In the rain
Posts: 761
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 59 Post(s)
Liked: 40
Quote:
Originally Posted by cap'n View Post

I'm just saying that my research and experience suggests that if you played back the typical concert hall recording on, for example, a full range stereo playback system and compared it to a bass managed system (as for example if you mono the bass and play it back over the two speaker in the same positions and eq it to remove any resulting spectral differences) the difference would be very subtle.

I agree, most recordings are wrong.

This doesn't indict the need for independent bass radiators, but it speaks loads about modern recording methods that don't account for 1940's level understanding of psychophysics...

The problem is simple, though. If we go to MPEG Surround, Parametric Stereo, and single subwoofers, we arrive at a state where proper production makes things sound worse, rather than better.

I think the audio industry is in enough of a mess, without pigeonholing itself into an "assured lower quality" situation.

James D. (jj) Johnston
jj_0001 is online now  
post #474 of 665 Old 01-15-2009, 07:23 PM
Advanced Member
 
jj_0001's Avatar
 
Join Date: Sep 2006
Location: In the rain
Posts: 761
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 59 Post(s)
Liked: 40
Quote:
Originally Posted by cap'n View Post

I dont understand your repeated mention of volume velocity. Our ears are pressure sensing organs.

Only in isolation. Torso, lower body, chair, etc, all interfere with the velocity field and create pressure at places where you might not expect it.

And the lower the frequency, the larger the "model" needs to be.

This is easily demonstrated in the 100+ Hz range, where you will find when you put your ear in a null in a bad room, it's not the same position as the null for a pressure microphone.

The effect is certainly less at 50 Hz. On the other hand, 40Hz is a wavelength of about 1152/40 = 28 feet (approximately), which puts a human at approximately a 1/4 wavelength, when you certainly do start to see interaction. (Yes, I'm aware most of us aren't 7' tall, but you don't have to hit a whole 1/4 wavelength to start to have an effect, either.)

Physics is fun.

James D. (jj) Johnston
jj_0001 is online now  
post #475 of 665 Old 01-15-2009, 07:47 PM
Senior Member
 
gedlee's Avatar
 
Join Date: Dec 2008
Posts: 350
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 13 Post(s)
Liked: 37
Todd

Thanks for the review. I agree that the cross correlation at the ears will be virtually one at LF no matter what you do. I also agree that the ears are pressure devices and I, for one, found the Greisinger discussion of velocity at LF rather obscure and could not see the relavance.

My work was strictly aimed at achieving a smooth spectral and spatial pressure response in the rooms center and the correlation or decorrelation at the ears was not of interest. I found that when one decorrelated the sources the smoothest response possible with agiven number of subs was achieved and that the sub locations was almost irrelavent - the setup was very insensitive to sub location. This seemed to me to be the ideal goal of LF reproduction in a small room.

Large venues (or any venue above the Schoeder frequency) are a different issue altogether and really is a completely different discussion. It's the lack of modes at LF in a small room that is the main problem of interest (for home theater at least) as this is a big hole in many, if not most, systems that I have heard.

Earl R. Geddes
GedLee
gedlee is offline  
post #476 of 665 Old 01-15-2009, 07:55 PM
AVS Special Member
 
QueueCumber's Avatar
 
Join Date: Sep 2005
Location: Farmer McGregor's Garden
Posts: 6,089
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 14
Quote:
Originally Posted by QueueCumber View Post

Can someone quantify at what volume a space is a large venue and no longer a small venue?

...

"It is worse still to be ignorant of your ignorance."
-- Saint Jerome (374 AD - 419 AD)

My Home Theatre
QueueCumber is offline  
post #477 of 665 Old 01-15-2009, 08:22 PM
Senior Member
 
gedlee's Avatar
 
Join Date: Dec 2008
Posts: 350
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 13 Post(s)
Liked: 37
There is no hard and fast rule. There is a frequency known as the Schroeder Frequency Fs above which a room is no longer modal in nature and below which it is. If this frequency is at the lower edge of what you consider the audio bandwidth then the room is "large" as there are no modal effects at all. The Fs in a car is about 200 Hz. In a small HT about 150 Hz, maybe lower, a large HT about 100 Hz. A class room is about 50 Hz. This is all dependent on the damping as large damping causes more modal overlap and Fs moves lower. The damping is what makes it hard to give concrete numbers based on volume alone.

Earl R. Geddes
GedLee
gedlee is offline  
post #478 of 665 Old 01-15-2009, 08:41 PM
AVS Special Member
 
QueueCumber's Avatar
 
Join Date: Sep 2005
Location: Farmer McGregor's Garden
Posts: 6,089
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 14
Quote:
Originally Posted by gedlee View Post

There is no hard and fast rule. There is a frequency known as the Schroeder Frequency Fs above which a room is no longer modal in nature and below which it is. If this frequency is at the lower edge of what you consider the audio bandwidth then the room is "large" as there are no modal effects at all. The Fs in a car is about 200 Hz. In a small HT about 150 Hz, maybe lower, a large HT about 100 Hz. A class room is about 50 Hz. This is all dependent on the damping as large damping causes more modal overlap and Fs moves lower. The damping is what makes it hard to give concrete numbers based on volume alone.

Thanks.

"It is worse still to be ignorant of your ignorance."
-- Saint Jerome (374 AD - 419 AD)

My Home Theatre
QueueCumber is offline  
post #479 of 665 Old 01-15-2009, 09:16 PM
Advanced Member
 
jj_0001's Avatar
 
Join Date: Sep 2006
Location: In the rain
Posts: 761
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 59 Post(s)
Liked: 40
Quote:
Originally Posted by gedlee View Post

Todd

Thanks for the review. I agree that the cross correlation at the ears will be virtually one at LF no matter what you do.

I refer you to the Johnston and Kuo paper cited above.

It measures crosscorrelation between channels, including lags larger than the microphone spacing, and shows rather a lack of cross-correlation with an appropriately spaced microphone array.

Velocity is very simple, really, it's maximum at a pressure zero, and minimum at a pressure peak. But I think you knew that, so I'm not sure what issue regarding velocity you're referring to.

But, in any case, it's quite clear that the human body is long enough to interact with a velocity field well below 100Hz. So perhaps we should examine that, yes?

James D. (jj) Johnston
jj_0001 is online now  
post #480 of 665 Old 01-15-2009, 10:59 PM
Member
 
cap'n's Avatar
 
Join Date: Jan 2009
Location: Los Angeles
Posts: 50
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Liked: 12
I agree that smooth response (spectally and spatially if there is more than one listener) is paramount. If you have to sacrifice that to get "bassiousness" (if that is even possible), it's not worth it. An i agree too that discussion of velocity is perhaps unnecessarily confusing, though perhaps it is more relevent to the recording end, where velocity sensitive microphones/arrays are used.

Now I will have to try the experiment in a small room where I measure with and without a human body to see how much effect there is on the measured response. I would be surprised if the difference was large below 100 Hz, I'm guessing the notches move around a bit.

I havent read the Johnston and Kuo paper yet, but again, aren't you talking about the recording end? ... and with directional mics and/or mic arrays? I was talking about playback in a room.

_____________
Todd Welti
cap'n is offline  
Reply Ultra Hi-End HT Gear ($20,000+)

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page


Forum Jump: 

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off