or Connect
AVS › AVS Forum › Audio › Audio theory, Setup and Chat › Do bass traps produce noticeable audible difference?
New Posts  All Forums:Forum Nav:

Do bass traps produce noticeable audible difference? - Page 3

post #61 of 191
Quote:
Originally Posted by amirm View Post

But by all means, post a physics formula that gives the curve I posted. I am pretty sure you cannot.

a physics formula??! lol. quoted for preservation of this nonsense.
post #62 of 191
Edited
Edited by GIK Acoustics - 2/20/13 at 7:04am
post #63 of 191
Quote:
Originally Posted by amirm View Post

While you are at it, do you want to explain why such things as speech intelligibility actually improve with more reflections than the other way around?

why don't you just inform us how speech intelligibility and articulation degrades in the absence of reflections when listening to a source material via that of headphones.


rolleyes.gif
Quote:
Originally Posted by armir 
Likewise, references to Schroeder and conditions for reverberant field are inappropriate in this context.

another day passes. still waiting for you to provide these "conditions for reverberant field".
post #64 of 191
Quote:
Originally Posted by localhost127 View Post

in a reverberant sound-field, the energy is so "well-mixed" that one cannot resolve a discrete reflection's gain, time-arrival, or vector/direction. an echo, by nature of being a specular return (with sufficient delay), contradicts this very definition.
I don't see a definition, but, anyway, so what? Is there some claim above about bass traps that hinges on whether you're right about this point of terminology? Why are you telling us this?
post #65 of 191
Quote:
Originally Posted by GregLee View Post

... Why are you telling us this?
He only has one hammer, so everything looks like a nail.

You and others will note that we've yet to see a rigorous definition of what he's railing about... this definition will, of necessity, be in the form of an equation, not words, and will define all parameters, as anything less is ambiguous.

I gave it a stab, and note that he replied to the dictionary definition... may not know what is meant by a "physics formula," or more likely realizes he's undone in that arena.

Have fun,
Frank
post #66 of 191
Quote:
Originally Posted by fbov View Post

You and others will note that we've yet to see a rigorous definition of what he's railing about...

Have fun,
Frank

define "rigorous definition".
Edited by localhost127 - 2/20/13 at 2:39pm
post #67 of 191
Quote:
Originally Posted by GIK Acoustics View Post

Ethan ... why you persist to argue that what you hear is reverb against his definition

I'm not convinced his "definition" is correct. Definitions can also change over time. I spent a good hour researching this, and found nothing to refute my opinion of what constitutes reverb. I might be mistaken! But so far all I've seen from Local is "you're wrong" with nothing to back it up but his say-so.

--Ethan
post #68 of 191
Quote:
Originally Posted by amirm View Post

Fact that the room reflections are not fully diffused in small spaces does not invalidate its use ... Again, the fact that the reverberations are not diffused is not important.

Thank you Amir. Yes, that's all I'm saying. I don't know why some people feel the need to pick apart every last bit of minutiae. As if they need to denigrate others to make themselves look smart. eek.gif

--Ethan
post #69 of 191
Quote:
Originally Posted by Ethan Winer View Post

I'm not convinced his "definition" is correct. Definitions can also change over time. I spent a good hour researching this, and found nothing to refute my opinion of what constitutes reverb. I might be mistaken! But so far all I've seen from Local is "you're wrong" with nothing to back it up but his say-so.

--Ethan

Sound System Engineering (davis/patronis)
Quote:
Reverberation is "the time in seconds that it takes a diffuse sound field, well beyond a real critical distance, to lower in level by 60dB when the sound source is turned off."

chapter 7 (large room acoustics, specifically, schroeder's F (sub) L) and chapter 8 (small room acoustics: non-statistical spaces).
it may be time to expand your knowledge on acoustics from what has been well known and understood for decades.

and you're right about "definitions changing over time", especially regarding that of "acoustic expert".
you're free to continue to use the word as slang. the problem is with the general population of which use the term reverb without being aware that they are using it as slang - such as what has been represented in this thread. as such, they then assume that RT60 is relevant in their small spaces - when in fact it is not. we have better (more appropriate) tools at our disposal to address small acoustical space energy behavior.

what's unfortunate (read: scary) is the utter unawareness of that of schroeder's entire career with respect to the subject of discussion.
Edited by localhost127 - 2/21/13 at 5:47am
post #70 of 191
Quote:
Originally Posted by localhost127 View Post

Sound System Engineering (davis/patronis)
chapter 7 (large room acoustics, specifically, schroeder's F (sub) L) and chapter 8 (small room acoustics: non-statistical spaces).
it may be time to expand your knowledge on acoustics from what has been well known and understood for decades.

and you're right about "definitions changing over time", especially regarding that of "acoustic expert".
you're free to continue to use the word as slang. the problem is with the general population of which use the term reverb without being aware that they are using it as slang - such as what has been represented in this thread. as such, they then assume that RT60 is relevant in their small spaces - when in fact it is not. we have better (more appropriate) tools at our disposal to address small acoustical space energy behavior.

what's unfortunate (read: scary) is the utter unawareness of that of schroeder's entire career with respect to the subject of discussion.

When you

  1. Learn how to write comprehensible sentences in English;
  2. Make a serious effort to punctuate, spell, and capitalize;
  3. Drop your confrontational, petty, and insulting demeanor;
  4. Can differentiate between slang, colloquialisms, idioms, jargon, dialect, common usage, technical usage, dictionary definitions, and specialized (nonce) definitions; and
  5. Read entire papers and books that both support your obsessive thesis and cast alternatives (such as Floyd Toole's work which you famously mock) instead of googling for "sound bytes" that bolster your one-man agenda;

Then you'd get a better hearing on some of the points you're trying to make. As it is, your lips are moving but no one can hear what you're saying because your presentation is that of a caricature (wildly screaming, hands gesticulating crazily, foam frothing from the mouth, legs kicking and flailing, pants around the knees) rather than a reasoned and intelligent presentation that people will actually listen to.

I'm not confident this post will have any net effect, but I had to at least try.
post #71 of 191
Quote:
Originally Posted by armir 
Likewise, references to Schroeder and conditions for reverberant field are inappropriate in this context.

another day passes. still waiting for you to provide these "conditions for reverberant field".
we'll continue to wait while you frantically put google to good use!
post #72 of 191
Quote:
Originally Posted by filecat13 View Post

When you
  1. Learn how to write comprehensible sentences in English;
  2. Make a serious effort to punctuate, spell, and capitalize;
  3. Drop your confrontational, petty, and insulting demeanor;
  4. Can differentiate between slang, colloquialisms, idioms, jargon, dialect, common usage, technical usage, dictionary definitions, and specialized (nonce) definitions; and
  5. Read entire papers and books that both support your obsessive thesis and cast alternatives (such as Floyd Toole's work which you famously mock) instead of googling for "sound bytes" that bolster your one-man agenda;

Then you'd get a better hearing on some of the points you're trying to make.

Excellent points. Local is behaving the same way in a parallel thread at Gearslutz, relying on face palm smileys instead of logic and good manners.

Also, the author Local quoted is just another non-degreed expert expressing an opinion. It's not a scholarly text. Don Davis is an expert for sure! But I see no evidence that his expertise necessarily trumps mine.

--Ethan
post #73 of 191
Quote:
Originally Posted by Ethan Winer View Post

Excellent points. Local is behaving the same way in a parallel thread at Gearslutz, relying on face palm smileys instead of logic and good manners

so you didn't read the very first response to you in that thread. also, you wish us to tell you what is reverb and then insist that we "ignore official definitions". lol!
Quote:
Originally Posted by Ethan Winer View Post

Also, the author Local quoted is just another non-degreed expert expressing an opinion. It's not a scholarly text. Don Davis is an expert for sure! But I see no evidence that his expertise necessarily trumps mine.

--Ethan

shoot the messenger! dance. deflect!

expertise?? these are well-established definitions! this is physics! this is measured behavior! you are apparently oblivious to any of this.

what does Don Davis have to do with the relevant information provided via the career-work of Wallace Clement Sabine and Manfred Schroeder? ..except for actually demonstrating the processes! you didn't even read the text - you google-searched one of the co-authors. you're obviously not interested in a knowledgeable discussion otherwise you would have the drive to explore and learn more instead of looking for the very first thing you can use in attempt to invalidate the authors.
Edited by localhost127 - 2/21/13 at 3:10pm
post #74 of 191
Quote:
Originally Posted by Ethan Winer View Post

Also, the author Local quoted is just another non-degreed expert expressing an opinion.

Patronis holds a Ph.D and is a Professor of Physics (not lecturer, a professor) at Georgia Tech.
https://www.physics.gatech.edu/user/eugene-t-patronis
If you open the book, his Ph.D is stated on the first page.

To state my point more clearly, I'll quote from the same book in Chapter 8, Small Room Acoustics:
Quote:
Originally Posted by Sound System Engineering, page 178 
What is often overlooked in the attempted measurement of RT60 in small rooms is that the definition of RT60 has two parts, the first of which is unfortunately commonly overlooked.
1. RT60 is the measurement of the decay time of a well-mixed reverberant sound field well beyond critical distance"

My point (to clarify) is not to prove one wrong about the reverb definition (I simply don't care the term one uses, I use the terms interchangeably depending on who I'm talking to), but to simply state: the RT60 calculation is useless in a small room.
post #75 of 191
Quote:
Originally Posted by Ethan Winer View Post

I'm not convinced his "definition" is correct. Definitions can also change over time. I spent a good hour researching this, and found nothing to refute my opinion of what constitutes reverb. I might be mistaken! But so far all I've seen from Local is "you're wrong" with nothing to back it up but his say-so.

--Ethan

I wasn't attempting to say either of you were correct.
Edited by GIK Acoustics - 2/21/13 at 12:33pm
post #76 of 191
Quote:
Originally Posted by GIK Acoustics View Post

Patronis holds a Ph.D and is a Professor of Physics (not lecturer, a professor) at Georgia Tech.
https://www.physics.gatech.edu/user/eugene-t-patronis
If you open the book, his Ph.D is stated on the first page.

To state my point more clearly, I'll quote from the same book in Chapter 8, Small Room Acoustics:
My point (to clarify) is not to prove one wrong about the reverb definition (I simply don't care the term one uses, I use the terms interchangeably depending on who I'm talking to), but to simply state: the RT60 calculation is useless in a small room.

+1
this discussion is not about someone's choice to use the word as slang. it's recognizing that one is using the term as slang and not attempting to apply calculations reserved for Large Acoustical Spaces that exhibit a statistically random-incidence reverberant sound-field in small rooms! it is also about recognizing the pre-requisites for the statistical calculations to even be considered valid! but that won't stop these guys from trying to fit a square peg into a round hole and saying "well, it sorta fits ... ".


professionals use the term reverb as slang quite often - but they understand the difference! the problem is with general novices who use the term without realizing they are using it as slang. any attempt to bring this to realization is met with heavy resistance, as indicated here. maybe it is an ego thing, as no one wants to admit they've been operating under the false impression of a word or behavior of energy for all these years. what's even more comical is some of these forum members that seem to imply that it is somehow my definition or that i am proposing this newly found phenomenon! i am merely the messenger for this well-understood and accepted behavior. when one has nothing else of value to provide on the subject: distract and shoot the messenger!

even dennis E agrees that RT60 is irrelevant in small rooms.
http://www.avsforum.com/t/1443066/oc703-on-bottom-of-soffits/0_60#post_22668729
Edited by localhost127 - 2/21/13 at 12:32pm
post #77 of 191
Quote:
Originally Posted by localhost127 View Post

Sound System Engineering (davis/patronis)
chapter 7 (large room acoustics, specifically, schroeder's F (sub) L) and chapter 8 (small room acoustics: non-statistical spaces).
it may be time to expand your knowledge on acoustics from what has been well known and understood for decades.

and you're right about "definitions changing over time", especially regarding that of "acoustic expert".
you're free to continue to use the word as slang. the problem is with the general population of which use the term reverb without being aware that they are using it as slang - such as what has been represented in this thread. as such, they then assume that RT60 is relevant in their small spaces - when in fact it is not. we have better (more appropriate) tools at our disposal to address small acoustical space energy behavior.

what's unfortunate (read: scary) is the utter unawareness of that of schroeder's entire career with respect to the subject of discussion.

Hey Local even Philip Newell uses the term reverberation time in his studio design book, though he caveats it with the normal it's not really reverberation time, since it's a small room, etc as do Amir, Ethan and I. It's accepted practice by many professionals that the concept is useful as a way to look at decay time across different frequency bands. Single figure RT60 isn't particularly useful or relevant. Whether we use the term reverberation time or decay time it doesn't really matter to me, it is only semantics, and it's clear that despite whatever is written in text books as the 'proper definition' in practice the use of decay time in small rooms is useful and relevant as demonstrated by many professional designers.
post #78 of 191
Quote:
Originally Posted by fbov View Post

...You and others will note that we've yet to see a rigorous definition of what he's railing about... this definition will, of necessity, be in the form of an equation, not words, and will define all parameters, as anything less is ambiguous....
Quote:
Originally Posted by localhost127 View Post

define "rigorous definition".

Reading comprehension is not your strong suit...
post #79 of 191
Quote:
Originally Posted by localhost127 View Post

Sound System Engineering (davis/patronis)

(the important stuff was here)

chapter 7.
The "important stuff" is a discussion of RT60, a measurement, NOT reverberaton time, a physical concept in acoustics. This is at least the fifth time I've said that.... can you hear me now?

BTW, dictionaries identify slang. I haven't seen anyone using slang... reverberate and time both have unambiguous definitions.
post #80 of 191
Quote:
Originally Posted by fbov View Post

... The predictive accuracy (of an RT60 measurement/calculation, ed.) may be compromised in small spaces, but the understanding conveyed is unchanged and the desired end result is identical. ...
Quote:
Originally Posted by GIK Acoustics View Post

...: the RT60 calculation is useless in a small room.

That reality has been recognized time after time, to no avail. Local's not using his hammer for any constructive purpose I can discern.

And I hate posting twice, much less three times in a row!
Frnak
Edited by fbov - 2/21/13 at 2:05pm
post #81 of 191
Quote:
Originally Posted by fbov 
... The predictive accuracy (of an RT60 measurement/calculation, ed.) may be compromised in small spaces, but the understanding conveyed is unchanged and the desired end result is identical. ...
Quote:
Originally Posted by fbov View Post


That reality has been recognized time after time, to no avail. Local's not using his hammer for any constructive purpose I can discern.

And I hate posting twice, much less three times in a row!
Frnak

may be compromised? it IS compromised!!! operator error!

can you elaborate on how: "the desired end result is identical".

can you elaborate on how the: "Waterfall shows RT" ?
Edited by localhost127 - 2/21/13 at 2:41pm
post #82 of 191
Quote:
Originally Posted by fbov View Post

The "important stuff" is a discussion of RT60, a measurement, NOT reverberaton time, a physical concept in acoustics.

what ??
post #83 of 191
Quote:
Originally Posted by localhost127 View Post

even dennis E agrees that RT60 is irrelevant in small rooms.
http://www.avsforum.com/t/1443066/oc703-on-bottom-of-soffits/0_60#post_22668729

And I've said so many times myself too. If you bothered to read my original statement in Post #37 of this thread more carefully, you'll see that I qualified it as being an empty room:
Quote:
Originally Posted by Ethan Winer View Post

Now, if you add "typically furnished" to "small acoustical spaces" then I'd agree. But an empty room can be highly reverberant, even if it's relatively small.

This is a very important distinction!
Quote:
Originally Posted by Nyal Mellor View Post

even Philip Newell uses the term reverberation time in his studio design book, though he caveats it with the normal it's not really reverberation time, since it's a small room, etc as do Amir, Ethan and I. It's accepted practice by many professionals that the concept is useful as a way to look at decay time across different frequency bands.

Exactly. And again, an empty room can definitely have enough individual echoes that they fuse together with sufficient density to sound like "reverb." When we say "a small room doesn't have real reverb" we are referring to a finished space, not the empty shell of a control room that's just been drywalled. Further, as someone aptly pointed out (was it here or at GS?), the live reverb chambers in professional recording studios going back 60 years are relatively small. Yet nobody disputes that you get real reverb from those rooms. Well, I guess know-it-all forum trolls will. Here's a good link:

http://audiogeekzine.com/2011/02/the-history-of-echo-echo-chambers-chambers/
Quote:
Originally Posted by History of Echo Chambers 
EMI Studios (later Abbey Road Studios) was a studio complex built by a record label at a time when it was hard to imagine a better business model than recorded music. There were 3 reverb chambers built inside the complex, one for every studio live floor.

Chamber One was built first for Studio Three (the smallest live floor in Abbey Road) and it made use of a single Tannoy speaker being heard by a Neumann KM53. It was approximately 11′ wide by 19′ long and was rectangular except for a diagonal reflective wall on which the speaker was focused.

Chamber Two was built to satisfy reverb needs for Studio Two (home of The Beatles). It likely made use of the same Tannoy and KM53. It’s dimensions were rather unflattering for an acoustic environment, featuring two pairs of parallel surfaces measuring 12′ x 21′. To make up for this, engineers pointed the Tannoy at one corner, and used sewer piping to diffuse standing waves in the room. Crude, but it hasn’t hurt sales of The Beatles catalogue.

Chamber Three was built for EMI’s classical studio work, mostly being done in the gigantic Studio One. It used staggered, nonparallel surfaces coated with the same reflective tiles as the other chambers. Measuring 17’8” by 12′, it was suitably the biggest chamber in the building.

The key is these rooms were empty, with only speakers and microphones, and the surfaces were often shellacked or tiled to be highly reflective at treble as well as midrange frequencies. And notice that the third studio listed was used for classical music!

--Ethan
post #84 of 191
Quote:
Originally Posted by Ethan Winer View Post

And again, an empty room can definitely have enough individual echoes that they fuse together with sufficient density to sound like "reverb."

sound like reverb?? or is reverb??

Quote:
Originally Posted by Ethan Winer View Post

When we say "a small room doesn't have real reverb" we are referring to a finished space, not the empty shell of a control room that's just been drywalled.

when i say reverberant sound-field i refer to a very-specific type of acoustical energy flows of which are required for statistical calculations to be considered valid. it's really that simple.
you are free to use it as slang as you have been. no one contests that.

from this point on i'll start using "acoustic specialist" as slang.
Quote:
Originally Posted by Ethan Winer View Post

Further, as someone aptly pointed out (was it here or at GS?), the live reverb chambers in professional recording studios going back 60 years are relatively small. Yet nobody disputes that you get real reverb from those rooms. Well, I guess know-it-all forum trolls will. Here's a good link:

http://audiogeekzine.com/2011/02/the-history-of-echo-echo-chambers-chambers/
The key is these rooms were empty, with only speakers and microphones, and the surfaces were often shellacked or tiled to be highly reflective at treble as well as midrange frequencies. And notice that the third studio listed was used for classical music!

--Ethan

again, as i've stated from the very beginning, long decay times do not automatically imply statistical reverberant sound-field!
what do you contradict with my statement?

oh, you mean they call them "reverb rooms" so they must imply reverberant sound-field?
well then - amp manufactures started including "reverb knobs" on their products many decades ago - maybe that induces real "reverb" from my speakers too.

Quote:
Originally Posted by Ethan 
Also, the author Local quoted is just another non-degreed expert expressing an opinion.

eating your own words yet?


don't worry, amir should be here any moment now to provide (google) you the "conditions for reverberant sound-field".
Quote:
Originally Posted by amirm 
Likewise, references to Schroeder and conditions for reverberant field are inappropriate in this context.
post #85 of 191
Sorry for the late response guys. Been travelling with non-stop meetings for the last few days.
Quote:
Originally Posted by GIK Acoustics View Post

To state my point more clearly, I'll quote from the same book in Chapter 8, Small Room Acoustics:
My point (to clarify) is not to prove one wrong about the reverb definition (I simply don't care the term one uses, I use the terms interchangeably depending on who I'm talking to), but to simply state: the RT60 calculation is useless in a small room.
You have not give us any independent data why you believe that. So let's go to the horse's mouth and examine how strong Davis' proof points are that such a measurement is "meaningless" as he states.

The section you are quoting is less than a page long and is titled, “Small Room Reverberation Times”. I will address the theory points he puts forward in another reply but for now, let’s examine the back up he puts forward in the form of a quote from Dr. Schultz’s 1963 AES Journal paper, ”Problems in the Measurement of Reverberation Time.” Unfortunately Davis' only shows you a snippet instead of the full context of that (very good) paper. I will remedy that here.

As the title indicates, the paper is about what can go wrong in measuring reverberation times using various techniques. He starts with this case study:

Consider the curves shown in Fig. I, which purport to display the reverberation time of a small rectangular room plotted as a function of frequency. The upper curve gives the reverberation time when the room is completely bare. It shows an extreme variation of reverberation time with frequency. The lower curves were obtained by adding progressively more sound absorptive material to the room.”

i-jtN2fsS-L.png
“CPS” is cycles per second or as we commonly call it, Hertz. So the chart’s horizontal axis ranges from 10 Hz to 10,000 Hz. He goes on to explain what is wrong:

”What, then, is the trouble with these curves? Surprisingly, there appear to be at least three methods of measurement which would give this kind of wrong answer! The first of these consists of measuring the reverberation in the room indirectly by means of a standard acoustical source of known power output. This method works fairly well in a large room in which a great number of the room modes crowd together and overlap in any reasonably small frequency band.”

So the key to the measurement being correct is having many modes overlapping. Where do we run afoul of this in our small rooms? He explains it:

“In a large room, if one has a large sound source whose power output is known, one can determine the total amount of absorption in the room by measuring the average pressure throughout the room. This total absorption can then be used to calculate the reverberation time from the Sabine formula. This method fails badly in a small room, however where, a large part of the spectrum of interest lies in a frequency range where the resonant modes of the room do not overlap but may be isolated , as shown in Fig. 1 (individual resonance peaks are identified with their corresponding mode numbers). In this case the microphone, instead of responding as a random sound field (as required for the validity of the theory on which these methods depend), will delineate a transfer function of the room. This is a curve which gives response in terms of modal frequencies, but only a little about the absorption on the boundaries. It does not provide a valid measurement for the reverberation time in the room however.”

The above is the only part of the paper quoted in Davis’ book except that he omits the sections in bold. When we add them in and focus on key sections I have highlighted in red, we realize that this is not at all supportive of the broad assertion made by Davis and you repeating the same. Dr. Schultz is focused on the modal region below 100 to 200 Hz and saying that we do not have many modes in small rooms so we better be careful in applying simple RT60 formulas.

What does this mean in English? Modes create peaks and dips in the room response at certain frequencies which we can theoretically predict using modeling. Let’s use Ethan’s tool and apply it to a typical home listening space which in acoustic domain is considered “small:”

i-PxzznK9-M.png

We see that at frequencies less than 100 Hz, the modes are indeed pretty sparse. To wit, below 50 Hz with have just one at ~28 Hz. Let’s compare this to a much larger room:

i-kTXnzWR-S.png

Quite a different picture emerges as we now get lots of room modes in the same low frequency area below 100-200 Hz. I want to reserve the theory of why we need many modes for the next post but for now, let’s accept what we want is what Dr. Schultz says: many modes for the reverberation times to be more accurate.

One “solution” to getting more modes is to do per above which is to have a much larger room. But there is another: move up in frequencies. Look at the density of modes on the right edge of our small room: it is starting to have lots of modes packed together much like what the larger room has at lower frequencies. Translating, if the RT60 measurements are accurate to a low frequency in large room, they are accurate just the same for small room except that we need to move up in frequencies.

If you search for my posts and countless peer reviewed literature in Journal of ASA and AES which use RT60 measurements in small spaces, the above is precisely the recommended practicethey do: the RT60 measurements are for “mid-frequencies.” I use 500 to 1000 Hz; others use the same or go up to 3 KHz or so. RT60 is not provided as a measure to evaluate modal (e.g. subwoofer) region. There we use frequency response to reveal the impact of the modes. Therefore, our practice and that of countless other researchers is very much in compliance with the concern that Dr. Schultz shares.

So the claim of the measurement being useless is not supported by the citation in Davis’ paper. He creates a scenario (using it in modal frequencies) and then shoots it down.

To be fair, at mid frequencies our modal distribution in a small room has not yet fully achieved Poisson distribution (discretely random in space and time but with a known long term average). I will address why this is not an impediment to analysis of our small spaces in the next post.

As if he knows that the Dr. Schultz point only applies to modal low frequency region, Davis’ next immediate section, 8.4 titled “Small Room Resonances” is a discussion of room modes!

Believe it or not the best part of this answer is yet to come! smile.gif In this section, he provides this graph:

i-zBkjj8j-M.png

Seems familiar, no? It is the exact same measurement as Dr. Schultz used sans the repeat sin of saying where it came from! eek.gif This is the text that goes with that graph:

”In Fig. 8-4, the effect of “undamped” modes are plotted, as a decay time, for small broadcast studio. The damping is provided by diaphragmatic absorption at the lower frequencies. “

Get it? He uses the very graph Dr. Schultz used to say represents wrong information, renames it to “decay time” and claims it now holds valid data!!! How could a measurement go from meaningless to so useful by just changing the term that way? Note how the graph still says Reverberation time! eek.gif

It gets more interesting. Dr. Schultz’s paper was published in 1963. The measurement above must have been performed prior to 1963 or else, Dr. Schultz could not have quoted it. The first revision of Don Davis’s book which by the way did not have professor Patronis involved came out in 1987. How is it that someone writing a text on acoustics has nothing more current and appropriate to use to demonstrate room modes than a measurement from some 25 years back??? And one that completely torpedoes his case just half a page back??? Your guess is as good as mine but I am afraid it indicates that maybe Davis did not read the Dr. Schultz paper either.

I don’t want to take anything away from Don Davis’ reputation or work. But let’s all agree that this is not how we go backing strong assertions. Take a look at the Dr. Toole coverage of the same topic and it goes on for tens of pages, encompassing research paper and data after research paper and more data. You can go read any of the original research as I have done and you will have a heck of a hard time invalidating the conclusions he draws from them. Everything in Dr. Toole’s case is referenced properly so that people can double check if they want. Not so here sadly.

Summary
Davis makes a very bold claim that RT60 measurement is meaningless. Folks proceed to repeat the same all of the Internet and hammer into people as gospel. Yet just one level of digging shows that the backup data Davis uses refers to not using RT60 for low frequency analysis. That is a non-point since the proper use of RT60 is for analysis of mid-frequencies, not modal low frequencies. Worse yet, Davis turns around uses what is said to be faulty data as his proof point for something else by just swapping names! I get believing in what experts tell us but come on now. People in the industry should at least dig one level further and read research references before believing.

As I noted in part two of this post (in the next few days) I will address the theory points Davis’ sites for those who really want to know “how the sausage is made.” smile.gif
post #86 of 191
Quote:
Originally Posted by GIK Acoustics View Post

but to simply state: the RT60 calculation is useless in a small room.

as you have eluded to (and myself to the point of sounding like a broken record), RT60 has pre-requisites in order to be considered valid. if you do not satisfy these conditions, then the results are erroneous and not valid. this is operator error. this is what happens when you put a user in charge of a tool they do not understand nor know how to use appropriately.

the first being that RT60 is the measurement of the decay time of "a well-mixed reverberant sound field well beyond critical distance"
eg, a sound-field where the energy is so well-mixed, one cannot resolve a discrete reflection's gain, time-arrival, or direction. an echo, as amir cluelessly eluded to, is not "reverb" as an echo's direction and time arrival and gain can all be resolved. a logical contradiction. when there is a clear lack of understanding of even the basic fundamentals, then mass confusion will follow (along with plenty of distractions employed to mask this fundamental misunderstanding).

since Reverberation Time (RT) is a characteristic of an acoustical space, this is also why one employs an omni-source (eg, a dodec) vs typical loud-speakers of which are not true omni-sources.

you'll notice that all of the proponents in this thread continue to ignore the fundamental fact that they cannot prove by any means that there is a point within their residential rooms where the reverberant sound-field (sic) is higher in gain than the direct signal. - and thus a point where they are in the "reverberation". they ignore this primary pre-requisite for RT60 in absolute. nor are they utilizing true omni-sources. they will stir up any distractions in order to escape from these clauses. i've asked ethan countless times to demonstrate this - he has not responded once regarding any notion of critical-distance. it is obvious that he cannot demonstrate that one exists such that we can then agree on what calculations can then be considered valid. the silence is deafening in this regard.

Quote:
Originally Posted by Sound Reproduction: Floyd Toole 

Figure 4.2 shows a familiar portrayal of idealized behavior in one of these
halls. In this depiction, an omnidirectional sound source is located well away
from the room boundaries, such as the center front of the stage. As a function
of distance from the source, the level of the direct sound follows the inverse square-
law rate of decay (−6 dB per double distance, dB/dd) until it encounters
the underlying steady-state reverberant sound field
that is assumed to extend
uniformly throughout the space (Beranek, 1986; Schultz, 1983). The distance
from the source at which the direct sound equals the level of the reverberation
is known as the critical distance (also known as reverberation distance or reverberation
radius).

Quote:
Originally Posted by Sound Reproduction: Floyd Toole 

In the abundance of reflections that we collectively
call reverberation, there are so many individual events
that it has been common to think of them as a statistical
entity distributed randomly in time and space
. As
a result, classic concert hall acoustical theory often
begins with the simplifying assumption that the sound
field throughout a large relatively reverberant space is
diffuse.

Quote:
Originally Posted by Sound Reproduction: Floyd Toole 

4.3.4 What Is a “Small” Room?
Diffuse-field theory may not apply perfectly to concert halls, but it applies even
less well to other kinds of rooms
. In the acoustical transition from a large performance
space to a “small” room, it seems that the significant factors are a
reduced ceiling height (relative to length and width), significant areas of absorption
on one or more of the boundary surfaces, and proportionally large absorbing
and scattering objects distributed throughout the floor area

These are not Sabine spaces, and it is not appropriate to employ
calculations and measurements that rely on assumptions of diffusivity
. Schultz
(1983) states, “The amount of sound-absorbing material in the room cannot be
accurately determined
by measurement, either with the decay-rate (reverberation
time) method or the steady-state (reference sound source) method. . . . One
cannot trust the predictions of the Diffuse Field Theory for a non-Sabine
room.”


Quote:
Originally Posted by Sound Reproduction: Floyd Toole 

4.3.5 Conventional Acoustical Measures in Small
Listening Rooms

A measurement of reverberation time in a domestic-sized room yields a number.
When the number is large, the room sounds live, and when the number is small,
the room sounds dead. The implication is that there should be an optimum
number. In spite of this, many thoughtful people believe that RT is unimportant
or irrelevant
(D’Antonio and Eger, 1986; Geddes, 2002; Jones, 2003; Kuttruff,
1998). The numbers measured are small compared to those in performance
spaces, and so the question arises if the late-reflected sound field in a listening
room is capable of altering what is heard in the reproduction of music. Yet, RT
is routinely included as one of the measures of small listening and control rooms
for international standards, even to the point of specifying allowable variations
with frequency.

Quote:
Originally Posted by Sound Reproduction: Floyd Toole 

Reverberation time is a property of the room alone, and a correct measurement
of it should employ an omnidirectional sound source
capable of “illuminating”
all of the room boundaries.
The reason for this is that it is assumed
that the boundaries consist of areas of reflection and absorption and that the
central volume of the room is empty. The several formulae by which we estimate
RT confirm this, and the values of absorption coefficient for the materials are
“random incidence” values, meaning that there is an assumption of some considerable
diffusivity in the sound field. Some practitioners incorrectly use conventional
sound-reproduction loudspeakers as sources
. The directivity of these
is such that the resulting reflection patterns and decays are not properties of
the room but of the room and loudspeaker combination—a very different situation.

Also, as we will see in Chapter 20, absorption at specific angles is quite
different from random-incidence absorption. Figure 4.15 illustrates the fundamental
difference between a proper RT measurement and what it is that we
listen to.


FIGURE 4.15 (a) How RT should be
measured, using an omnidirectional source
aiming its sound at all of the room surfaces,
and an omnidirectional microphone.


yes, Reverberation Time is a "property of the room alone". this is why we measure "well past critical-distance" such that the direct signal is merely driving the reverberation and NOT imparting on the measurement itself (via the direct signal). !!!


Quote:
Originally Posted by Sound Reproduction: Floyd Toole 

In a small listening room, we are in a transitional sound
field that consists of the direct sound, several strong early
reflections, and a much-diminished late-reflected sound
field. What we hear is dominated by the directional characteristics
of the loudspeakers and the acoustic behavior
of the room boundaries at the locations of the strong early
reflections. RT reveals nothing of this. As a measure, it is
not incorrect, but it is just not useful as an indicator of
how reproduced music or films will sound. Nevertheless,
excessive reflected sound is undesirable, and an RT measurement
can tell us that we are in the ballpark, but for
that matter, so can our ears or an “acoustically aware”
visual inspection.

so yes, if the extent of your requirements is merely to "ball-park" tongue.giftongue.giftongue.gif
so can our ears and visual inspection. tongue.giftongue.giftongue.gif

Quote:
Originally Posted by Sound Reproduction: Floyd Toole 

It is therefore necessary to conclude that the
large-room concept of critical distance is also irrelevant in
small rooms.

well, there goes the fundamental pre-requisite for Reverberation Time, of which is that the measurement is to be taken "well past the critical-distance". tongue.giftongue.giftongue.gif
but hey, we're only interested in "ball-parking", right?

Quote:
Originally Posted by Sound Reproduction: Floyd Toole 

The numbers produced by traditional acoustical predictions and by measuring
instruments, while not totally irrelevant, are simply not direct answers to
the important questions in small rooms used for sound reproduction
. What,
then, are the important questions? The accumulating evidence suggests that
they have to do with reflections but not in a bulk, statistical, sense. We need to
understand the influences of early reflected sounds. This means that the knowledge
base must include the directivity
and off-axis frequency responses of loudspeakers
and the directional reflective, diffusive, and absorptive characteristics
of materials at the points of first reflections.
Only with this information can we
predict the sounds that might arrive at listening locations in rooms,
and only
with careful experimentation can we understand the perceptual effects that they
cause. This is very different from traditional acoustics.

RT tells you nothing with regards to the time-arrival, vector (direction), and gain of the focused specular reflections that are prominent in small acoustical spaces.
this is because by nature, RT is a with respect to a sound-field where one cannot resolve any reflection's time-arrival, vector (direction), and gain! eek.gif


Quote:
Originally Posted by amirm 
Likewise, references to Schroeder and conditions for reverberant field are inappropriate in this context.

and amir STILL has yet to be able to produce the very easily referenced information that dictates the "conditions for reverberant sound-field" of which would then indicate RT can be valid.
the silence is deafening! but the frantic google searching is heard loud-and-clear.
post #87 of 191
Nice post Amir. I suspect it's falling on deaf ears. eek.gif

Am I the only person rolling his eyes at the irrelevant minutiae the reverb deniers are spouting? As I said, if it looks like a duck...

--Ethan
post #88 of 191
and since toole cites schultz repeatedly, let's go straight to the horse's mouth:
Quote:
Originally Posted by Ted Schultz --- formerly of Bolt, Beranek and Newman 

In a large room, if one has a large sound source whose power output is known, one can determine the total amount of absorption in the room by measuring the average pressure throughout the room. This total absorption can then be used to calculate the reverberation time from the Sabine formula. This methods fails badly in a small room, however where, a large part of the spectrum of interest lies in a frequency range where the resonant modes of the room do not overlap but may be isolated…In this case the microphone, instead of responding as a random sound field (as required for the validity of the theory on which these methods depend), will delineate a transfer function of the room…It does not provide a valid measurement for the reverberation time in the room.”*

What is often overlooked in the attempted measurement of RT60 in small rooms is that the definition of RT60 has two parts, the first of which is commonly overlooked.

1.) RT60 is the measurement of the decay time of a well-mixed reverberant sound field
Well beyond Dc (the critical distance).
2.) RT60 is the time in seconds the reverberant sound field to decay 60 dB after the sound source is shut off.

Since in small rooms, there is no Dc (critical distance), no well mixed sound field, hence no reverberation but merely a series of early reflected energy, the measurements of RT60 become meaningless in such environments.

What becomes most meaningful is the control of early reflections because there is no reverberation to mask them.”


small spaces are dominated by modal region resonances and focused specular reflections - neither of which are "reverberation".


the salesman is merely concerned with "ball-parking" of which can just as easily be performed with our own ears and vision - per toole.
no actual acoustical analysis of the space, just ball-parking.
Edited by localhost127 - 2/23/13 at 5:54pm
post #89 of 191
Quote:
Originally Posted by amirm View Post

The above is the only part of the paper quoted in Davis’ book except that he omits the sections in bold.

Don didn't just quote Ted Schultz ... Schultz was activily involved in Syn-Aud-Con!

rolleyes.gifrolleyes.gifrolleyes.gif
Quote:
Originally Posted by amirm 
It gets more interesting. Dr. Schultz’s paper was published in 1963. The measurement above must have been performed prior to 1963 or else, Dr. Schultz could not have quoted it.
Quote:
Originally Posted by amirm 
but I am afraid it indicates that maybe Davis did not read the Dr. Schultz paper either.

LOL - Ted Schultz had an on-going relationship with Don Davis. were you not aware of this? rolleyes.gifrolleyes.gifrolleyes.gif of course you weren;t.
Ted Schultz, who Toole actively cites!!!

you have no understanding of the history of that which you are attempting to discuss. you are merely trained in google and copy-paste searches.
Edited by localhost127 - 2/24/13 at 6:43am
post #90 of 191
Quote:
Originally Posted by Ethan Winer View Post

As I said, if it looks like a duck...

merely applying a label does not always make it so.
Quote:
Originally Posted by Ethan Winer 
And again, an empty room can definitely have enough individual echoes that they fuse together with sufficient density to sound like "reverb."

sounds like reverb or is reverb?
Edited by localhost127 - 2/24/13 at 6:41am
New Posts  All Forums:Forum Nav:
  Return Home
  Back to Forum: Audio theory, Setup and Chat
AVS › AVS Forum › Audio › Audio theory, Setup and Chat › Do bass traps produce noticeable audible difference?