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Review and Discussion of Toole's Book, Third Ed.


Chris A
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Floyd Toole has become a figure not entirely unlike PWK: he represents a knowledge base in sound reproduction and identification of relevant measurements that correspond to listener preferences. This stands in contrast to what I consider to be a general wasteland and land of confusion and folklore memes filled with pseudo-science and belief systems not backed up by fact.  His newly updated and very recently released 3rd edition of his notable book: Sound Reproduction--The Acoustics and Psychoacoustics of Loudspeakers and Rooms has been largely rewritten and somewhat refocused.  I think that this new book deserves a review and some discussion.

 

Chris

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Tom,

 

I haven't completed the entire book, but what he is saying about room treatments is actually related to his broadened discussion on "early reflected energy" and "room curve" discussions in the latter parts of the book (chaps 5, 12, 13, etc), which is in my opinion very subtle and easy to misunderstand.  In fact, that is a major reason why I started this thread.  Toole's discussion of "room curves for loudspeakers" is actually talking about the off-axis early reflections, not the direct arrival energy from the loudspeakers.  I was very amazed to read that Toole handled those discussions in the way that he did, since he also stated that "directivity issues are not correctable by EQ, etc.".  

 

Since Toole is showing direct-radiating loudspeakers (with only minimal "directivity correcting" recesses...horn loading...on the HF drivers for the 2-5 kHz region), what he is saying is that loudspeaker placement plus room acoustic treatments must be arranged to achieve his "Toole curve" early reflection energy curve.  I didn't get that from the first edition book (even though he might have said it there).  It's laid out fairly explicitly in the third edition book at section 12.2.  He doesn't hit you over the head with that idea, however, unless you're reading very carefully. 

 

So far, that is the biggest change in that subject from the first edition.

 

Chris

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So some notes on the rest of the book...

 

The first section of the third edition is quite a bit different than the 1st edition (note that the 2nd edition is identical to the 1st edition--so there really are only two versions available).  I think that Toole decided to "dumb it down" a bit in order to reach more audience.  To me, his first edition reads much better as a hyperlinked pdf file than a real book.  The cross references are much more prevalent in his 1st edition than in any other physical book that I've ever read, and that fact slows down the reading of the book considerably if using paper.  I think that Toole wanted to access an audience that was a little less "academic".

 

Looking at the new front chapters of the 3rd edition, there are several points that can be made:

 

Toole makes light of the issues with recorded music EQing, based on inferior studio monitor performance (the "Yamaha NS-10M" problem), and tells the reader that there are many more issues with "translation" of music recordings from the recorded tracks to the mastered products.  He's even less deferential about those mastering issues than I've been highlighting in the "Missing Octave" thread (i.e., demastering) and others.  This is a bit of a departure from the 1st edition, in terms of its visibility and in discussions on the "Circle of Confusion".  He makes some good points on the movie industry vs. the music industry, and really gives the music industry a very subtle "cold shoulder", if you read carefully.

 

Looking at section 1.6 (The Role of Loudspeakers and Rooms), Toole pulls very few punches.  One quote that I picked up on:

 

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...it will be shown that loudspeakers are the single most important element in sound reproduction.  Electronic devices, analog and digital, are also in the signal paths, but it is not difficult to demonstrate that in competitively designed products, any effects they may have are small if they are not driven into gross distortion or clipping.  In fact, their effects are usually vanishingly small compared to the electro-acoustical and acoustical factors.  Tests of these effects quickly become exercises in "is there or is there not any difference?"  This was the origin of the well-known ABX test, which has shown with monotonous regularity that well-designed power amplifiers, loudspeaker wires, and the like are not responsible for offensive sounds.  Occasionally, a test may show that a difference was observed at a level of statistical significance. 

 

Another quote from section 1.6:

 

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If we are to set an objective for loudspeaker performance, it should be timbral neutrality...Loudspeakers should not be part of the art.

 

and finally from section 1.6:

 

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Traditionally, loudspeakers have been chosen "by ear"--subjectively.  Underlying this is the widespread assumption that "we all hear differently," so it has to be a personal decision...But in the end of blind evaluation two things were clear:

(1) most listeners agreed on what they liked, and
(2) the loudspeakers that they liked had the best looking (i.e., smoothest and flattest) frequency responses...

Now we can identify "neutrality" by looking at the right set of measurements.  Very neutral sounding loudspeakers are available to both professional and consumers, and many of them are at affordable prices.  The difficulty is in identifying such products because comprehensive and trustworthy performance data is rarely exhibited. 

 

Toole comes across as very restrained in his comments on these subjects, but when you read carefully, his comments are actually quite scathing in scope and severity.

 

...and he also got a lot of brownie points from at least this reader for saying those things so clearly...

 

Chris

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Chapter 2 is a very brief one that defends the "scientific method" when applied to product design and review.  It merely sets the stage for the chapter to follow: turning subjective opinion into fact.  It has little other purpose that I can see.

 

Chapter 3 turns the part of turning subjective opinion into fact: blind-blind testing procedures and why they're done the way that they are. 

 

The problem that I see with this is that most of this chapter seems to be aimed at engineering enterprises on the edge of making a decision to build those expensive blind-blind testing facilities.  Either that or the author is trying to impress his reader that he knows more than they do about this subject--that the notions of turning subjective listening opinions into facts can't be questioned.  Not that I want to question it, but there are "chinks in the armor", so to speak, that must be addressed in one or more tests referenced.

 

Combine this with an issue that is to come in the next chapter (Chapter 4 - The Dimensions of Sound, a tutorial on psychoacoustics)--specifically the portion on the in-audibility of harmonic and modulation distortion, and that the entire subject is avoided in discussion throughout the book, ostensibly because it is "too engineering-oriented" and "too hard to quantify into direct measures of listener displeasure".  This is, for me, a source of my most severe problems with the book's focus.

 

Chris

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Just a note at this juncture: it may seem that I'm "biting the hand that's feeding" (i.e., the author's) in doing a more critical review of Toole's 3rd edition but the fact is that the book itself is a wonderful addition to the first book in terms of the amount of otherwise good information provided.  I recommend buying it and reading it.  It will help with many conceptions and misconceptions on the subject of audio reproduction--along with its 1st edition companion that's available in pdf on the Web.

 

However, I've coined a term in the past which I call "The Life-Raft Theory".  Basically, it goes something like this:

 

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When you're in the ocean treading water and waiting for someone to come along and rescue you, anything that floats looks like a life raft--a solution to all your immediate problems

 

In reality, things that float (depending on latitude) can include swimming polar bears transiting large bodies of water to reach their migrating prey, or even perhaps a field of Portuguese man-of-wars (i.e., the stinging kind).  In these cases, our personal expectations at the moment probably are out of line with the perceived opportunity.  In these instances, it is perhaps better to leave well enough alone and continue to tread water, patiently waiting for true rescue.

 

In the case of Toole's book, there is a tendency to want to use it to solve all of our problems on audio.  So when we see a perceived deficiency, the knee-jerk reaction is to criticize it more vocally than we might otherwise do for less useful information sources.  In the case of Toole's book, since it tends to be so comprehensive in nature and high in quality of information provided, there is a strong tendency to be especially critical. 

 

I can only assure you that I'm aware of this tendency, but will make my excuses for any critical remarks as I go--the kind of which the reader I believe needs to know, and illustrated with the "why" or rationale of why it is so important to understand the other side of argument.  It may change your entire outlook--and the eventual makeup of your listening room full of expensive audio equipment.

 

Chris

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I'm humbled.:blush2:  Hopefully there might be others that post in this forum from time to time that are also worthwhile to read.

 

I'm winding up for the next "at bat": chapter 4 of Toole's book, which has many insights...and issues...of which I feel that it is necessary to strike a careful balance.  That little "caveat emptor" that I posted above was an attempt to set the right tone for the  discussion. 

 

There have been some time consuming distractions here of late:

 

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That's Duncan...our little "brown warrior".

 

Chris

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Okay, we get to the "tutorial" (as Toole calls it) of Chapter 4 The Dimensions of Sound.  In my view, this portion of the book sets the foundation for the rest of its pages, so the title of this chapter is perhaps somewhat less than I'd call it.  For me, this chapter should be called "Basic measurements" and later on in the chapter..."Author Assumptions on Loudspeakers/Rooms".  The first part is pretty mundane and relatively noncontroversial--except for figure 4.3 (figure 19.2 in the 1st and 2nd editions).  This figure tells you a story:

 

image.thumb.png.2bf08c9eb1dc3aa604a33878686ae8e0.png

 

First off: the scale on the right is in electric (amplifier output) watts instead of acoustic watts.  Toole is assuming that the speakers that you buy are about 87 dB at one watt (electric) input.  That's about 10 times more power than your typical Klipsch loudspeaker will need, i.e., 97 dB at one watt input at one metre.  [If you run fully horn loaded like Khorns, La Scalas, Belle or Jubilee, that 1 watt is 100 times too much input power since these loudspeakers are ~105 dB per one electric watt input at one metre.]

 

This tells you something about the author's assumptions already and I have to say...it's not promising.  Categorically, Klipsch owners are not represented by this assumption of such low efficiency and such low expectations of what the loudspeakers/room should be capable of.

 

Secondly: he is saying that the average SPL in a home theater (and I assume he's talking SPL at an average seat location and not at the loudspeakers--is at least 10 dB lower than in commercial movie theater.  This could be an incorrect assumption).  Most people that I know only listen at such low levels at home if they:

 

a) have nearby sleeping children, other adults, and/or pets that they don't wish to awaken (and poor sound insulation around the HT to keep sound out of the sleeping quarters),

'b) have overly sensitive hearing (and I know many people who have this medical condition--which I do not have),

c) they have really crappy loudspeakers in a really bad listening environment

d) they have huge rooms for their HTs and are listening many metres from the loudspeakers themselves

 

To design your home theater to be so limited in its capabilities as what is shown in the figure above is probably something that many people that do not own Klipsch have to live with.  Fortunately for the rest of us that do own much more capable loudspeakers, we're not limited to such anemic average SPL for movies--all we have to do is turn the volume control to the right a little more and we get "the real thing"--movie theater levels, easily.

 

More to come...

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  • 2 weeks later...

Toole's books are actually a bit difficult to judge due to the nature of their "internal linkedness" and implied choices based on other less described observations or choices. 

 

In the case of loudspeaker distortion (i.e., resonances, harmonic, modulation [FM and AM], compression, low & high frequency roll-off, etc.), what he mentions in the 3-4 pages that he talks about it (particularly in section 5.5 of the 3rd ed.), Toole is making a link between the price of the loudspeakers and their relative freedom from nonlinear distortions, assuming that all loudspeakers of approximately equal price will perform approximately equal in terms of distortions, and that these distortions will not make a difference in terms of double blind listening preferences. 

 

What I've found, however, is that this particular subject really exposes Dr. Toole's biases and prejudices based on the "current consumer loudspeaker marketplace", i.e., bought loudspeakers from large companies that "don't rock the boat". 

 

In the case of his viewpoints on this subject that means that he's assuming virtually all consumer-grade loudspeakers are direct radiating ones (mentioned above in the power needs or implied sensitivity ratings).  But if what he is saying were true, then no one would be buying Klipsch or other multiple entry horn designs--i.e., horn loaded designs.  What Toole is saying is that he assumes that lower price loudspeakers will have more distortions in approximately equal measures, regardless of the brand or model, and that loudspeaker distortion is not significant in the double-blind testing results. This is patently incorrect in my experience.  I believe that he knows this, too, but he is making grand sweeping assumptions to "simplify the subject for his readers".   I believe this is a fundamental mistake made for the balance of the book.  While there were comments in the 1st edition that softened this viewpoint, in the 3rd edition, Toole has removed those very comments.  Toole has excised the material from the 1st Ed in section 18.2.3 on horn-loaded loudspeaker testing (specifically the JBL K2-S9500 loudspeaker) and its typical placement at the top of the double blind ratings against all other loudspeakers tested. In this particular case, I can't give him the benefit of the doubt: it looks as if he is pandering to his former employer's lineup of direct-radiating loudspeakers. 

 

In my experience, once you throw well designed and implemented horn-loaded loudspeakers into the mix of reviewed loudspeakers, the playing field is no longer a level one in terms of performance/cost , and the well-designed horn loaded models--even by his own admission in the 1st edition--will significantly outperform the direct radiating models in blind testing.  I believe in this new edition of the book (the "3rd"), Toole further obfuscates the comments that he made in the 1st edition. 

 

This is disappointing in that I really did expect the reasoned judgments of his career in loudspeaker and room testing to shine a light more brightly in his 3rd edition than in the 1st edition on the basic listening differences in this area (distortions).  The fact that he didn't says to me that he either is pandering to his former employer, or that perhaps the span of years has taken a toll on his judgment.  Perhaps it's more of the latter with regard to "not rocking the boat".  I don't know.  What I do know is that that the subject of the relative levels of nonlinear loudspeaker distortions is pivotal at this point in both of his book's editions, and is my initial point of departure from the advice given within.  Toole is clearly laying down to the perceived limitations of price to performance and making those choices for us--poor ones in my experience.

 

In the case of large loudspeaker companies that must charge large price margins (in excess of 250% on hardware costs) on their products to support their large organizations, this may seem reasonable.  But in my experience, the future of the loudspeaker marketplace is open to disruption from small and "boutique" shops offering considerably more value for money--shops that can now do the engineering using the tools that are available at considerably lower cost than in past decades.  In this case, those old choices of "well, the customer can't afford better sound" simply no longer holds true.  I'm thinking of how Dell computers did business: no products are made in advance of the customer's order, and only until then, is anything bought--and using only the customer's money.  The entire supply chain is transformed to providing maximum customer value for money, not standing armies of marketing, finance and accounting, and related fixed facility and insurance costs that do nothing for the actual customers.

 

So those implied choices of what the customer can get for his/her money are no longer specifically valid and the high cost of loudspeaker design, analysis and test have now gotten affordable to entry-level competitors with the knowledge base in the basic engineering and knowledge of psychoacoustics. Toole actually tried to make a case for further increase in development and test costs over the present, but in my estimation--one that's unconvincing.  The present marketplace says that manufacturing and related business costs should be coming down...drastically.

 

Chris

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I first read passages of the book....online no less and free....on your reco Chris.  It was great and so helpful.

 

With that said i agree with much of what you say and will go further -- i get that toole is one of the great gurus of showing some science behind what was often good guessing.  

 

But i look at his living room theater -- mediocre honestly, no real effort to have a dedicated room and say to myself and now the2 forum - he is brillant but obsolete.

 

We (the community) have gone beyond his initial findings and have created a very advanced world of home theater and 2 channel sound.

 

I could not agree more the comments of 87db sensitivity was fine in the earlier edition but klipsch is beyond popular now and a top brand.  Not addressing this tells me his studies from decades ago are what hes got and hasnt really attempted to step up to see todays situation.

 

He was an early proponent of horns and constant directivity or at least controlled directivity but doesnt seem to be moving with the times.

 

Even his theories on treatment....that minimal treatment is ideal....may again appeal to the masses and be "reasonable"....but are long past proven not to be ideal.

 

Ive reviewed designs for a hundred studios, theaters and the like and minimal treatment is not ideal.  It is the minimum!

 

With that said i greatly appreciate his contributions but moreso yours Chris.  Your willingness to call foul is a good thing.

 

There are some basic questions most of us have that he can answer definitively and its my understanding that before him that was not the case.

 

Imo its darn exciting to be at what is really still the early stages of truly great audio reproduction.

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One thing that I didn't wish to do is to call Toole's overall knowledge "dated"--because I don't believe it is.  I believe that he's probably forgotten more than any of us have learned on the subject. 

 

What I'd take issue with is his conclusions on what makes the best decisions on loudspeaker configurations at different price levels.  Similarly, I take issue with his notion that things should be getting tighter in terms of performance tolerance and more difficult/ expensive to measure, and his seemingly heavy over-reliance on the frequency response curve to the exclusion of more problematic nonlinear distortion measures (especially for the readers of his book).  I would invert some of his implied design trade choices.

 

I think he's going in the wrong direction with his assumption that "good loudspeakers don't have to be able to play very loud, but rather with very flat frequency response", especially with his notion that people can live with modulation and compression distortion at higher SPL.  I think that he's dead wrong on that topic, in fact.

 

Predicting the future isn't something that is easy to do in any profession, and audio is one subject that's equally difficult to call.  I've found however that fundamentals apply no matter what your world view (gestalt) tells you it should be.  One of those fundamentals is that people can easily discern low distortion from higher distortion loudspeakers at low distortion (modulation and compression), and that people want loudspeakers that can play very low and very high SPL, no matter what.  The notion that "hi-fi" is quiet--less than 70 dB--is definitely a dated idea.  If people can get wide dynamic range without nonlinear distortion and with good bass extension at the same price of "hi-fi loudspeakers" (i.e., very limited SPL direct radiating loudspeakers), that's what they're going to do, not what other people tell them is "proper hi-fi".

 

Chris

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On 9/14/2017 at 6:57 AM, Chris A said:

in-audibility of harmonic and modulation distortion, and that the entire subject is avoided in discussion throughout the book, ostensibly because it is "too engineering-oriented" and "too hard to quantify into direct measures of listener displeasure".  This is, for me, a source of my most severe problems with the book's focus.

 

How did PWK quantify them?  I think I remember the Khorns having 1% modulation distortion at a certain SPL and the Cornwalls having 3% modulation distortion at a lower SPL.

 

To me, the Khorns had tighter, cleaner more precise bass, and somewhat clearer midrange.  I used to hang out in two stores who had both Khorns and Cornwalls (in the 1970s and early 1980s)  Was that likely due to a difference in modulation distortion?

 

The direct radiators that, indeed, had the flattest response tended to sound muddy and boring to me.  The first one I encountered was the AR series of acoustic suspension speakers.  Low definition!  Reportedly, Edgar Villchur and PWK were in attendance at the same Hi Fi Fair.  I wish I could have been a fly on the wall!  Consumers Reports magazine back then seemed to define "accuracy" as being flatness of frequency response, period.  Their top rated speakers tended to be inarticulate compared to the better Klipsch, JBL, EV, etc., i.e., horn loaded.

 

 

 

 

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13 hours ago, garyrc said:

How did PWK quantify them?

Gary, I believe that PWK did some anecdotal tests in the 60s, since he wasn't doing psychoacoustics per se.  The table 1 entry in his 3-part white paper on modulation distortion (1968) listed 0.7% modulation distortion (50 Hz and 300 Hz playing) at 100 dB/2 feet for a "well-designed bass horn", while direct radiating woofers had at least 5x the same level of modulation distortion.  I assume he is talking about a Khorn bass bin vs. a Cornwall bass bin, since I don't believe that he had other bass bins available.  As you know when the subject was modulation distortion, PWK focused his efforts on the bass bins where all the harmonics and sidebands would be extremely audible, and not so much on midrange.

 

What is important to note is that Toole is basically abandoning the entire subject of nonlinear distortion in his book (both editions) because he says that he doesn't have clean measures for "just detectable distortion" for the various nonlinear distortion types and under what conditions, so he just lumps everything into the "too hard bucket", then proclaims that all loudspeakers are "basically not affected" in terms of listener preferences to nonlinear distortions.  But then Toole goes on to detail at least one horn-loaded (midrange-tweeter) loudspeaker (the K2) that always ended up on the top of the listener preference list, without acknowledging the work of PWK, Beers & Belar, or subsequent Klippel measurements of modulation distortion in acoustic drivers and the relative levels of AM and FM distortion vs. frequency.  I'd call that disingenuous. 

 

The fact remains that more work on classifying audibility of "just detectable distortion" needs to be done or perhaps published if it already exists...which I suspect it may be in the case of JBL.  I find that companies categorically fail to publish the results of internal studies when the answers turn out to be "not to the management's liking". 

 

Chris

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I think you're right on target as to how us horn folks have to read between the lines with Toole's books, so you're providing a valuable service with this analysis.

 

Still, there is lots of good info to be had, e.g. the chapters on bass are chock full of info that's more generally applicable regardless of what your mains are.

 

 

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9 minutes ago, Ski Bum said:

Still, there is lots of good info to be had, e.g. the chapters on bass are chock full of info that's more generally applicable regardless of what your mains are.

I really don't want this statement to be lost in this discussion since little of this would be talked about if Toole's book didn't exist.  It's been a wealth of information--on other loudspeaker/room acoustics subjects.

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Dr. Toole has been posting on an AVS thread, and I have been thinking about posing the following questions on that thread.  Basically, I’m wondering if there are situations where flat frequency response is trumped by other factors.  I have not read his books, so perhaps these areas are covered in the books.  I should read a book.  :)

 

1) Distortion vs. SPL:

As SPL increases, is there a point at which a lower distortion speaker with less flat frequency response is preferred to a higher distortion speaker with a flatter frequency response?  For example, let’s say that at 80 dB, the flatter frequency is preferred, but at 95 dB, could lower distortion dominate preference vs. frequency response?

 

2) The listening room – dead vs. live:

Can preference swing away from flat frequency response depending on whether one’s room is at the extreme of reflective vs. absorptive for high frequencies?  For example, in a large, relatively dead room, could one prefer a speaker that has more high frequency output vs. a flatter speaker?

 

3) One’s hearing:

If one’s high frequency hearing is diminished due to age or other factors, could one prefer a speaker with more high frequency output vs. a flatter speaker?  Could this factor plus the dead room factor be additive in terms of one preferring a speaker with more high frequency energy?

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By the way the following website mentioned in the book and on the various sales web pages doesn't exist, or at least it hasn't been made publicly accessible as of this date: 

 

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The robust website (www.routledge.com/cw/toole) is the perfect companion to this necessary resource.

 

I think that Toole would have benefited greatly if he had set this up on his 1st edition book--leading to an even more improved 3rd edition.  Reader questions and feedback I find is usually very helpful in improving the quality and comprehensiveness of the printed material.

 

I think the answers to your second and third questions, above, have been at least partially addressed in both editions. I'm pretty sure that the answer to both your questions #2 and #3 above are a guarded "no".

 

As far as your first question: there are adjustments to loudspeakers having some directivity--but not constant directivity vs. frequency above the transition frequency of the listening room.  These are typically there to correct for the precedence effect of the human hearing system, the reflectivity of the room, and the lack of off-axis directivity control vs. frequency.  I've witnessed this myself.  But nowhere do people like to hear loudspeakers with non-flat frequency response unless the source music has significant problems with mastering EQ that has been used.   In general, all of Toole's tests tend to use music with much flatter mastering EQ used than is typical.

 

As I stated above, I believe that Toole has shied away from discussions on nonlinear distortion (which is proportional, albeit non-linear in loudspeaker output SPL) and frequency response flatness at the listener's ears at higher than 80 dB.  This is the same problem that Geddes ran into when he published his report on the audibility of modulation distortion--he wasn't able to get data for listening conditions higher than 80 dBA at the listener's eardrums (OSHA).  Geddes later acknowledged that there are indications that his statements of the inaudibility of modulation distortion might not hold for SPL greater than 80 dB (a bit sheepishly, I might add). I have reason to believe that Toole listens to his loudspeakers typically at very low levels compared to what most home theater enthusiasts typically do. 

 

Chris

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