Audio Critic the 20 r schematic

Issue No. 20

211 amperes peak current for $1100!

(See the power amplifier reviews.)

Retail price: $7.50

In this issue:

We launch our power amplifier survey with seven reviews for openers, circuit critiques, a new method of measuring dynamic performance into complex loads, and an amplifier tutorial by Dr. Rich.

The latest-and-greatest DCM "TimeWindow" is reviewed, along with other interesting loudspeakers.

We report our initial tests of the DCC system. Part III of the Ranada interviews with the elite of

audio brings you yet another original thinker. Plus other test reports, editorials, our

famous "Hip Boots" column, letters to the Editor, and lots of CD reviews.

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Issue No. 20 Late Summer 1993 Editor and Publisher Peter Aczel

Contributing Technical Editor David Rich Contributing Editor at Large David Ranada Technical Consultant Steven Norsworthy Columnist Tom Nousaine Cartoonist and Illustrator Tom Aczel Business Manager Bodil Aczel

The Audio Critic® (ISSN 0146-4701) is published quarterly for $24 per year by Critic Publications, Inc., 1380 Masi Road, Quakertown, PA 18951-5221. Second-class postage paid at Quakertown, PA. Postmaster: Send address changes to The Audio Critic, P.O. Box 978, Quakertown, PA 18951-0978.

The Audio Critic is an advisory service and technical review for

consumers of sophisticated audio equipment. Any conclusion, rating, recommendation, criticism, or caveat published by The Audio Critic represents the personal findings and judgments of the Editor and the Staff, based only on the equipment available to their scrutiny and on their knowledge of the subject, and is therefore not offered to the reader as an infallible truth nor as an irreversible opinion applying to all extant and forthcoming samples of a particular product. Address all editorial correspondence to The Editor, The Audio Critic, P.O. Box 978, Quakertown, PA 18951-0978.

Contents of this issue copyright © 1993 by Critic Publications, Inc. All rights reserved under international and Pan-American copyright conventions. Reproduction in whole or in part is prohibited without the prior written permission of the Publisher. Paraphrasing of product reviews for advertising or commercial purposes is also prohibited without prior written permission. The Audio Critic will use all available means to prevent or prosecute any such unauthorized use of its material or its name.

For subscription information and rates, see inside back cover.

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Contents

The Tweaks vs. the Pros: Is It a Bona Fide Debate Between Two Points of View?

By Peter Aczel, Editor and Publisher

A New Look at Medium- and High-Priced Power Amplifiers

By David A. Rich, Ph.D., Contributing Technical Editor

28 Boulder 500AE 29 Bryston 4B NRB 30 Dynaco Stereo 400 Series II 32 Hafler Series 9500 Transnova 33 R.E. Designs LNPA 150 35 Rotel RB-990BX 36 UltrAmp Power Amplifier

Three Speaker Systems in the 2.5 to 3.5 Kilobuck Range: Two Big and One Small

By Peter Aczel and David Rich

39 DCM TimeWindow Seven 41 Monitor Audio Studio 6

42 Snell Type B Minor

A First Look at Perceptual Coding and the DCC

By Peter Aczel

44 Marantz DD-92

Top-of-the-Line Pioneer Elite Video Equipment

By Peter Aczel

47 55" Rear-Projection TV: Pioneer Elite PRO-106 48 Laser Videodisc Player: Pioneer Elite LD-S2

Outboard D/A Converter Followup: Upgrades by EAD

By Peter Aczel

50 EAD DSP-7000 Series II and DSP-1000 Series II

From Tweak to Weasel (in One Easy Step)

By Tom Nousaine

Interviewing the Best Interviewees in Audio: Part III

By David Ranada, Contributing Editor at Large

57 7. Interview with Ken Kantor, Speaker Designer and Research Director

Hip Boots Wading through the Mire of Misinformation in the Audio Press

By the Editor and David Rich

65 Recorded Music A Mixed Bag of Recent CD Releases

By David Ranada

Box 978: Letters to the Editor

ISSUE NO. 20 • LATE SUMMER 1993 1

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From the Editor/Publisher:

Are We at All Catching Up with the Schedule?

This is always the last page I finish before a new issue goes off to the printer, and as I am writing this we are well into September but technically it's still summer. (A couple of days ago we had one of the hottest days of the year here in Bucks

County.) Now, this is the Summer 1993 issue—for safety I labeled it Late Summer 1993—and I am hoping that, technically, it doesn't become an early fall issue. That

would create a traffic jam because the real Fall 1993 issue will also have to be

published before the fall is officially over; at this point late November is the absolute

best we can hope for, and it will more likely be early December (I just hope it won't be

snowing yet). Obviously this is not the most desirable state of affairs, but somehow

our quarterly must keep up with the four seasons of the year, and if it does we will

have made some progress.

The latest development is that I have found a highly competent, widely respected, literate, and definitely unontweako " audio journalist whose name will go

on the masthead of the next issue as Assistant Editor. This savvy professional may actually be able to do half of my work, in which case it should take only half as long as before to finish each issue. 'Tis a consummation devoutly to be wish 'd. Lest I should jinx a situation with a previous history of bad luck, I am withholding the name

until Issue No. 21 is a reality. (Who says I can't be superstitious just because I'm not

a tweako audio cultist?)

While on the nagging subject of our publishing schedule, I want to respond to a

very small number of nasty letters whose tone renders them unfit for publication but whose message should be addressed. How dare we use a slogan like "Accountability in audio journalism," these fulminators write, when we are late all the time? Well, to me accountability in audio journalism means that we carefully measure the audio components we review in a well-equipped laboratory, do our comparative listening double-blind at levels matched within ±0.1 dB, and have our technical discussions double-checked by graduate engineers. Other "alternative" audio publications fail to do that. Accountability in publishing, on the other hand, means that we deliver four big, fat, lovingly edited issues for every $24 you send us, whatever the interval between them, and cheerfully refund the unused portion of your subscription if you ask for it. When it comes to speed of publishing, I must respond with the words of the bumper sticker I saw recently on an old car: "Bear with me—I'm pedaling as fast as I can."

Arrivederci in... well, late fall.

THE AUDIO CRITIC

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Box 978

Letters to the Editor

This is a column for letters of general editorial interest. That classification covers a lot of ground but emphatically does not include things like "I have a Schlockmeister M-100 power amplifier and I'm wondering if I should move up to something better—what do you folks recommend?" Not that we answer letters like that privately, either, because our business is magazine publishing, not private consulting. Letters printed here may or may not be excerpted at the discretion of the Editor. Ellipsis (...) indicates omission. Address all editorial correspondence to the Editor, The Audio Critic, P.O. Box 978, Quakertown, PA 18951.

The Audio Critic:

At the last two Consumer Elec-

tronics Shows (Summer 1992 and Winter

1993), room acoustics correction devices based on digital signal processing (DSP) were shown by Snell Acoustics. The first time Snell used DSP from SigTech and the second time they had their own, developed with Audio Alchemy (the tweako digital jitterphobes). The second time, SigTech also displayed independently. The demonstrations were accompanied by pushy proclamations of a "revolution in sound." One repeating claim was that the processors "make the room disappear." When the hype stopped and I was able to listen to their contrived A/B comparisons, I was not impressed.

I would like to use your magazine as a forum to state my concerns about this technology and to, hopefully, get some questions answered.

DSP questions:

Do responsible people on the inside, like Kevin Voecks of Snell, really believe all the hype? Can DSP fix a room with poor acoustics to make it just as good as one starting with good acoustics? Can

DSP create an acoustic environment better than any possible real room? If the DSPers will commit to a "yes" answer to any of the above, then when can we test a conventionally optimized system/room against an "improvement" by adding DSP? Is there a reason why this preference test cannot be double-blind?

DSP concerns:

DSP room correction is different from conventional room equalization in that it is able to make corrections in the time domain as well as the frequency domain. Actually, fully correcting the amplitude versus time (time domain) measurement of a signal automatically corrects the amplitude versus frequency (frequency domain) measurement, but the converse is not true. Conventional equalizers do a good job of correcting problems produced by the speaker system but not problems produced by room reflections.

Consider a speaker, a listener, and a single reflecting wall. Sound from the speaker travels both a direct path and a (longer) reflection path to the listener. The acoustic pressures add at the listener,

but not in phase because of the time difference caused by the path length difference. The resulting frequency response is a series of peaks and nulls called a "comb filter" response. For steady sine waves, this could be equalized to flat, but that would not fix the basic time domain problem, which is two arrivals.

Now let's deal with the problem in the time domain, using DSP. The problem is now simply the two arrivals, not a complicated comb filter response. Since DSP makes us time-domain-agile, we will feed our speaker a delayed and polarity-inverted version of the original signal. This will arrive at the listener just in time to acoustically cancel the signal reflected from the wall. Now the sound is "equalized" in both the time and frequency domains.

Perhaps you already see the ugly gremlins lurking in the background of this happy picture. First, the delayed signal designed to cancel the reflected sound also creates its own reflected sound, which needs to be canceled. This could go on forever except for the finite number of instruction steps available in the DSP. Fortunately, because of the longer path

ISSUE NO. 20 • LATE SUMMER 1993 3

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length of the reflected sound and because

of imperfect reflection, the reflected

sound is not as loud as the original. This

means that each correction signal is of a smaller amplitude than its predecessor. Hopefully, by the end of the processing time (900 milliseconds for the Snell system), the umpteenth correction of the correction is small enough to be neglected.

Let's try an example. Say the speaker is ten feet away and a reflection from a plaster wall takes an additional two milliseconds to arrive. By my calculations, the reflected-sound SPL would be 1.86 dB lower than the direct. Thus, the inverted canceling signal should also be 1.86 dB less than the original. Its own reflection would be down another 1.86 dB and so on. After 54 corrections of the corrections, the amplitude would be more than

100 dB below the original—small enough for further corrections to be neglected. At 2 milliseconds per correction, this would take only 104 ms, well within Snell's processing time.

Of course, the real listening rooms we want to correct are much more complicated. Acoustic energy radiated by the speaker does not simply encounter one or more early reflections, pass our listener, and disappear. The walls contain the acoustic energy within the room, allowing it to leak out relatively slowly.

This is measured by reverberation time.

Let's consider a very simple sound

from one speaker, a tick approximating a mathematical impulse. This tick of energy radiates in all directions covered by the speaker, encounters walls, and continues on (attenuated by the reflection) to encounter more walls. For the listener, the density of the ticks arriving increases with time, while the average amplitude of the ticks is reduced with time. The increase in density and decrease in amplitude are a function of room characteristics, particularly diffusion. For the usual listening room, the reflection density increases geometrically to extremely high values. A DSP acoustics corrector must be programmed with this "impulse response" in order to cancel it and to cancel a portion of the infinite series of equally complicated corrections of the correction signals.

Not only is it an awesome task to correct for a simple "tick" in a room, but such correction must be performed continuously on two channels of music in real time. We can label ourselves gullible if we believe this without asking for

proof that it has actually been accomplished.

Next we have the matter of what is meant by "acoustic cancellation." Here, it means that at some point (where the listener is), the pressure components of two sound waves cancel. Note that this is only at a point (or possibly a line or plane). The total acoustic energy in the room is unaffected by this local cancellation. Consider that we are dumping considerable energy into the room to achieve cancellation at a point. Even if cancellation at the listener is perfect for 900 milliseconds, won't this reverberating sound byte garbage be audible after this time?

Even in the aforementioned simplified situation of a speaker, a listener, and a wall, the total energy of the 104

milliseconds of corrections for the corrections is more than 1.34 times the original sound energy. This reverberant sound is not canceled; it is a problem which is simply pushed back in time. When the time is up we have a bigger problem.

Imagine the tick with one reflection.

For 900 milliseconds after the original sound, the speaker emits a decaying series of in- and out-of-polarity ticks totaling more than 1.34 times the energy of the original, for the purpose of preventing the listener from hearing a single

reflection. We must demand a demonstration that this is possible. We must demand a demonstration that the dumping of additional energy into the room has made the acoustics better, not worse.

Now we come to another point (literally). This is the "point" at which the cancellation occurs, the location of the listener. Listeners have two ears separated by six or eight inches, depending on whether you measure through or around the head. Acoustically, these cannot be considered to be the same point except at the lowest audible frequencies.

Example: Two pressures are equal and opposite at the left ear of a listener, say, arriving from one of the two stereo speakers and a sidewall reflection. The arrival-time difference for the two ears is likely to be around 0.4 millisecond. Therefore, at the right ear the phase of the problem signal and its canceler will be shifted, resulting in imperfect cancellation. At 200 Hz, the cancellation at the right ear will be only -18 dB, not a figure that is really acceptable like -100 dB. Remember, this is at 200 Hz. Lower frequencies will have better cancellation, but the effect will deteriorate at higher

frequencies until, at 600 or 800 Hz, there will be no cancellation at all.

The example was for a single listener optimally positioned in the sweet spot. For listeners who move or rotate their heads, the cancellation will be diminished. For other seating positions, all bets are off.

Stepping back from implementation issues for a moment, we might ask if the room-correction goal of acoustically "removing the room" is a worthwhile one. Real sound in a concert hall can be thought of as having infinite channels— sound comes from every direction. We use two channels for practical reasons.

The fact that we have two ears is no more an excuse for limiting ourselves to two reproduction channels than two eyes would be an excuse for using two spotlights to illuminate a room. Two channels are an okay compromise only because we have a listening room to supply delayed sound from other directions. Remove the listening room by using an anechoic chamber and you have bad sound. So, let me ask the question: Assuming DSP room correction can be successful, do we want our listening-room reflections removed?

Snell's earlier demonstration offered an A/B switch between straight through and processed. I thought I heard improved "equalization" via processed, but accompanied by a distinct "computer sound" echo on male speaking voice.

This echo was not audible to me on the music that I tried. The second showing did not offer an A/B comparison. The reason why not was said to be too complicated to explain. I remain a skeptic and I demand A/B comparisons to be convinced there is merit to this new DSP application.

Sincerely, David Clark DLC Design Farmington Hills, MI

/ was eagerly looking forward to the

Snell demonstration at the Summer CES (June 3-6, Chicago), but then Snell canceled their participation in the last minute—one of the many letdowns of the show—and none of us got to see and hear the latest version of their DSP technology. The reasoning behind your reservations is powerful and convincing, but let us wait until everybody's cards are on the table before we pass final judgment.

—Ed.

THE AUDIO CRITIC

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The Audio Critic:

It is with great trepidation that I enter this fray. Especially after making a significant sacrifice to put a Krell amplifier into my system because it did musical things for me that no "lesser" product could do. Moreover, I can describe the essential superiority in unambiguous musical terms.

A bass soloist, singing a Handel aria, was having professional difficulty with a low note. Through comparable amplifiers, this fact was obvious with Krell, detectable with PS Audio, and inaudible with Adcom. This hierarchy was clear, unmistakable, and unaffected by relative volume levels. This one note ultimately led to my purchase of a Krell amplifier.

In an effort to rationalize my action, I have come to refer to this characteristic as "resolving power"—the ability of an amplifier to respond to and reproduce the most subtle forms of musical informa-

tion. It was very clear with the three in-

struments involved that the threshold of "resolving power" was different in each

case.

It follows that if a specific musical event is masked, so will all the musical information below the threshold of resolving power represented by that event. I am convinced that such information is what is often referred to as air, depth, spaciousness, ambience, focus, soundstage, and the like. And, indeed, my gen-

eral subjective reaction to the three in-

struments mentioned would have to be

described using such terms. So, too,

would the differences between my Krell amplifier and the one it replaced.

What's the point? Unless semantics are playing tricks with me, my observa-

tions differ from many I have come

across over the years, and they might just

be of value.

1. "Definition" and "resolving power" are not the same. Adcom, PS Audio, and Krell are fine, high-definition amplifiers with varying degrees of resolving power.

2. Competently designed and manufactured modern amplifiers do not sound the same. In the absence of an appropriate and definitive musical event, however, the differences are difficult to identify reliably and describe objectively.

3. If a difference can be heard, it can be measured, but one needs to know where to look. Frequency bandwidth, power bandpass, and freedom from noise

ISSUE NO. 20 • LATE SUMMER 1993

and distortion all help, but mostly with different and less subtle problems. Information relating to resolving power, on the other hand, is audible even at the lowest listening levels and represents a tiny portion of an already tiny signal.

4. If I were looking to define resolving power, objectively, I would do two things: (a) Perform a circuit design and execution analysis of comparable Adcom, PS Audio, and Krell instruments to determine what causes the progressive masking of extremely subtle musical information. (b) Look to measure differences in the behavior of the instruments as the informational content approaches zero—both with respect to threshold and speed of response.

5. Let me concede that I also admire Krell products for the beauty of their industrial design and build quality, and ac-

cept the effect of these factors upon their cost. How nice it is that both physical and musical prowess can coexist in the same instrument.

I am directing this admittedly selftherapeutic letter to you because my reading of your journal suggests that you, particularly, may respond with interest.

Sincerely, Paul P. Siegert Geneva, IL

You're a dangerous man, Paul, a potential corrupter of the minds of novice audiophiles who might cross your path. You're obviously intelligent, articulate, analytical, self-confident, familiar with the audiophile scene, and therefore plausible—but you happen to be 100% wrong! What you write is basically tweako rubbish, put forth with a bit more class and suavity than I generally see in my day-today tweako mail. There is no such parameter as your "resolving power, " distinct and separate from frequency response, noise, static and dynamic distortion, power-supply characteristics, etc., etc. Your suggested investigations under 4(a) and (b) are inherent in our current test protocols. There is nothing in the electronics textbooks, nor in the IEEE or AES literature, to support your tiny-portion-ofan-already-tiny-signal nonsense.

The Krell vs. PS Audio vs. Adcom experience you describe took place, I suspect, in an audio salon—didn't it?— under the tutelage of a "coach" (i.e., a salesman who wanted to sell you a Krell). If you had reported that you were able to pick out the Krell double-blind, at levels

matched within ±0.1 dB, seven times out of eight replays of that low note of the bass soloist, then I would begin to believe that your perceptions had some validity. Since you say that the differences were

"unaffected by relative volume levels," I know right away that there was a lot of completely undisciplined volume-control twiddling, and it's also quite apparent that the test wasn't blind. You went through a meaningless exercise, Paul, and ended up with an extremely expensive amplifier that in reality sounds no different on that low note but is wellengineered, beautifully built, and solidly backed by a reliable company. Worse things could happen to an audiophile, so you really don't have to rationalize your compulsive purchase with science fiction.

One more observation. When I hear the word "speed" applied to the reproduction of instruments by an amplifier, I know I'm in tweako territory and start walking rapidly toward the border.

—Ed.

The Audio Critic:

It's always fun for me to read your witty and often acrid writing—except when I think that your remarks might be aimed at me. I'm referring to the admonishment to your readers, inserted just before the "Letters to the Editor" section of Issue No. 19, that many of us have written "letters that should never have been sent..." Since I recently wrote you a letter that I consider to be "intelligent, wellinformed, and well-written" (your words), but which was not published, I cannot help but wonder if I am among those committing "reciprocal punditry."

No, my feelings aren't hurt because my letter was not published, nor will they be if this one is not. The topics and questions in my letters may not be interesting to other readers, in your opinion, and that's OK, because it's your magazine. But I do think that this letter should be sent, because you are treading on thin ice when you seem to insult a broad, unidentified spectrum of your readership, and you also run the risk of causing the timid among us never to write a letter. Your magazine cannot survive without subscribers.

Certainly you may, and should, expose fuzzy thinkers and deflate pompous "experts" in your inimitable style, because that is why, I think, that many of us subscribe to The Audio Critic. But I hope you can confine your attacks to specific

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letters, articles and advertising claims, and not sweep all us unpublished letterwriters aside because we are cluttering your mail...

Sincerely, Sheldan C. Collins Weehawken, NJ

It never ceases to amaze me how touchy some people can get when they perceive, reading a totally impersonal

journalistic generalization, that somehow

"the shoe fits." In your case it fits twice,

both in the above letter and in the one

that wasn't published. The above letter extensively quotes my introduction to this column in the last issue but characteristically omits the crucial sentence: "Because they ask questions and bring up arguments that have already been answered in our pages... " I.e., not because you're "cluttering" our mail—wasn't that quite clear and readable? So once again it appears that you 'd rather write than read. Your unpublished letter asked questions about power line conditioners to which you could have read the answers, perhaps not in minute detail but certainly in all essentials, on page 60 of Issue No. 16. Your subscription record indicates that you have that issue.

Anyway, you have succeeded getting

yourself published, although you're prob-

ably not satisfied with the context. Thank

you, in any event, for your complimentary

remarks—and don't feel inhibited about writing, as long as it follows attentive reading.

—Ed.

The Audio Critic:

Here's what I call "News from the

Moronosphere."

Speed of light c in vacuum:

2.997924563x108 meters per second,

or 186,282.396 miles per second.

Propagation speed of electrical signal through wire (according to Dr. David Goodstein, Chancellor of Cal Tech and Professor of Applied Physics): between

0.8c and 0.6c for theoretically "pure copper" and junk wire, respectively.

Using the slower speed to obtain the shortest wavelength from a given signal:

186,282.4x0.6=111,769.44 miles per

second.

For wavelength, we divide propagation speed by frequency. If we use 20 kHz as the highest frequency at which audiophiles can "hear" phase shift, we get:

111,769.44÷20,000=5.59 miles, or

29,507 feet (per each 50 µs).

A quarter wavelength at 20 kHz is

1.4 miles long in the wire. And finally, dividing the wavelength

by 360°, or one entire cycle, we get:

29,507÷360=81.96 feet. A speaker cable long enough to ex-

hibit 1 degree of phase shift at 20 kHz would be 82 feet long!

Even in the face of incontrovertible

proof such as this, these boneheads still insist that they can hear phase anomalies in 30 feet of cable. It makes you wonder if they even know what "phase" is.

Drew Daniels

North Hills, CA

What they surely don't know is what

"hearing" is. They think hearing means

telling yourself and your friends that

you're hearing something. You don't

have to prove it; you just have to assert it. And you can't be tested to find out whether you're really hearing what you

claim to be hearing because the test will

inhibit your hearing ability. It's a closed system and it seldom gets to the point of scientific analysis, such as you present.

—Ed.

The Audio Critic:

...audio professionals think I'm crazy because I like to play with tubes! Can't help it, can I, if I happen to like a little tube distortion? I know you think tube audio is nonsense, but hear me out.

On page 5 of your Issue No. 19, you say that tube audio "has little or no support in the professional engineering community." Please see the enclosed articles from Mix and R·E·P. The use of tube audio processing is a major part of the professional recording business; highly respected recording engineers and producers go shopping for a studio partly on the basis of its supply of tube compressors, equalizers, microphones, and sometimes even mixers and tape recorders. Few or none of these pros are tweak audiophiles; in fact, most of the ones I've met over the years have never heard of "high-end" audio.

Not all tube companies are "tweaky" —outfits like AKG, Sennheiser, Summit Audio, Tube-Tech, Demeter, EAR, and some others are making tube electronics strictly for the pro audio world These people use tubes for their peculiar distortion behaviors and their dynamic-range capabilities. None of this has anything to do with the tweak world. (Although EAR

does make the usual overpriced amps and preamps for high-end sales, they also

make more conventional studio equipment, such as mic preamps, using tubes.) Not to mention VTL's Manley line.

And don't forget the tube guitaramplification market, more than $100 million worldwide last year and growing after several years of decline. Guitarists tend to like that tube distortion, plus have a legitimate need for amps that can take overloads without damage and without the interference of protection circuits.

(Rock guitarists have a tendency to destroy amps that go into protection in the

middle of a song.)...

The best part of making tubes a hobby is the continued availability of good, low-cost tubes. I don't really agree with you about them wearing out, at least preamp tubes. Good ones will give full gain for 100,000 hours and more, routinely. That's almost 12 years of continuous operation—I routinely see old hi-fi equipment, with preamp or driver tubes 30 and 40 years old that still work like freshfrom-the-box tubes. Power tubes are a bigger problem; typical beam-power or pentode power tubes are only good for

4000-5000 hours at best. This is why, if

someone who comes to me wants to ex-

plore the tube sound, I tell them to start

with preamps—tube power amps require

too much maintenance for most people. But when the tubes do wear out, there are plenty of reasonably priced replacements coming in from China, Russia, and the Czech Republic, and the supply is expected to continue for a long time— mainly to fill the needs of the guitar amp,

pro audio, and industrial markets....

Who am I? I do have a B.S.E.E., so snow jobs carry no weight with me. I'm a contributing editor at Glass Audio, probably the only regular contributor who doesn't tweak or believe in tweaking.

(Most of GA's construction projects are amps and preamps that are made for extreme accuracy; i.e., they end up sounding like solid state.) That's a whole strange political situation; I regularly get attacked for saying things like "why bother making a tube circuit sound perfect, unless it's just a technical exercise? If you want perfect, transistors are more practical. If you use tubes, use them for their own unique characteristics." Some of Ed Dell's subscribers are themselves would-be tweak gurus, and my position is upsetting to them...

Good luck with your magazine. If

THE AUDIO CRITIC

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those jerks in Santa Fe can reach 70,000 readers, then you can too. More easily I think.

Sincerely, Eric Barbour Albuquerque, NM

What you say is absolutely true, but what I said was also true. I should perhaps have written "professional E.E. community" instead of "professional engineering community," thereby excluding the recording engineers, who can be every bit as unscientific as the tweakiest audiophiles. They get paid for their ears, musical taste, and hands-on experience, not for their profound insight into electronic circuitry.

When a recording engineer swears by a piece of classic tube gear, it may very well be that no exact solid-state equivalent of it is available and that the manufacturer keeps selling it year after year; it doesn't follow, however, that no exact solid-state equivalent of it can be designed by a competent E.E. If you ask an E.E. professor at the Massachusetts Institute of Technology to design for you, say, a compressor—or even a guitar amplifier—from the ground up, he isn't going to reach for the tube manual. He will do it with solid-state devices, and he will be able to give you any "peculiar distortion behavior" and any "dynamicrange capability" you want. That was all I was trying to say. I never said there was anything inherently wrong with tube equipment already in use in someone's studio or home.

Yes, an old 12AX7 is much more likely to be in working condition than an old 6L6, but a 741 op-amp will easily outlive them both, barring some sort of catastrophe.

As for the Atkinson, Archibald, and Santa Fe, my tracks are laid elsewhere and go to different destinations, so it's hard to make projections about future

passenger traffic. My little engine keeps

saying, "I think I can!"

—Ed.

The Audio Critic:

Your magazine is a true pleasure to

read. Dr. Rich is a wonderful addition.

Sincerely, Hillel J. Kumin Associate Dean College of Engineering The University of Oklahoma Norman, OK

ISSUE NO. 20 • LATE SUMMER 1993

Confucius say, "One gracious compliment from engineering-school dean worth suffering one thousand indignities

from untutored tweaks." Thank you.

—Ed.

The Audio Critic:

I was delighted to see you [namely the Ed.] again in Chicago; I trust you had a fine time carrying the fight against audio fallacy into the hotel suites of the ig-

norant. ...

I am certainly a fan of The Audio Critic; in addition to its fine reviews and tutorials, I admire its stand against the uninformed and feel privileged whenever my name is invoked against the forces of sloth and stupidity. Please keep up the good work. The audio industry and its many enthusiasts need your help.

Sincerely, Ken Pohlmann Professor of Music Engineering University of Miami Coral Gables, FL

As an audio journalist and editor I

try to earn the respect of academics and

professionals who know more than I do,

such as you, Ken; the semieducated gurus of the various branches of high-end audio obviously seek the respect of those who know less than they do. I think that's a defining distinction, and it's great when someone with your credentials confirms it—so I'm the one who feels privileged.

But what's this sloth business, Ken? Every tweako audio journalist I can think of is busy as a bee; it would be nice if they were a bit slothful now and then.

—Ed.

The following six letters comment, pro and con, on the general subject one could call (with somewhat superficial brevity) "tweak bashing" or "ignoramus hunting." The Editor responds to them as a group.

The Audio Critic:

.. .In these post-Enlightenment times

it is alarming to note the general spread

of know-nothingism in many areas of

life, and particularly to see voodoo practitioners attempting to pass themselves off as scientists and engineers. The Audio Critic provides a welcome rational voice

in the audio community....

...I do wish that you would cease

and desist with the "Hip Boots" column. It's not that I think it's not both in-

formative and amusing, but it is rather like watching a microbiologist explain bacteria to a witch doctor. I personally would prefer to see more time, energy, and space devoted to information than to rebuttal of misinformation; besides, I believe Darwin was right, and with any luck the charlatans and snake-oil salespersons

(just to be fair to EL) won't reproduce....

Sincerely, Terrence McCarthy Brooklyn, NY

The Audio Critic:

...Your "Hip Boots" columns are superb. Is there any industry dominated by bullshit as much as high-end audio? I subscribed to The Absolute Sound almost from the first issue, until I realized that Enid Lumley was not a self-parodying invention of the reviewers. Then I realized that a company like Adcom could market the perfect amplifier (they haven't) at $800 list and not do better than Class C in Stereophile.

You would do your readers a great service if, as sort of an adjunct to "Hip Boots," you would list all of the gadgets called "accessories" in the high-end press and indicate whether the products are very useful, not worth the money, or a downright fraud. You wouldn't even

have to mention brand names, since we all will identify the products.

Keep up the "good worth." Your

publication is a real bargain.

Edward Doyle Weaverville, NC

The Audio Critic:

...I have read your most interesting Issues No. 16, 17, and 18, and am impressed with the objectivity with which the products are evaluated. However, temperate use of language may be far more effective than the scathing attack on those who do not review the products as

objectively as you do....

C.K. Vissanji Bombay, India

The Audio Critic:

Keep 'em coming. After Issue No.

10, I canceled my subscriptions to Stereo- phile and Hi-Fi News & Record Review. The Audio Critic is the "smart bomb" of audio journalism—always right on target and always devastating.

Sincerely, Chris L. Walker King of Prussia, PA

pdf 9

The Audio Critic:

I have decided not to renew my subscription to The Audio Critic. At first, I rather enjoyed your editorial style. Four issues later, I think the constant putdowns of the two other audio journals, their editors, and writers have become very tiresome.

Very truly yours, John Overman, M.D. Independence, MO

The Audio Critic:

As a new subscriber to your magazine, I recently received, and read, Is-

sues No. 16, 17, and 18....

The way you test audio products, with the emphasis on the facts and the use of a reliable, scientific, reproducible method, is very professional, useful to your readers, and refreshing.

Before going further, I feel that I must tell you a little more about my back-

ground and my experience in the audio field.

In 1978, I created a company, called

Architecture & Physique Appliquée. Our products were sold under the name Gold-

mund, until the beginning of 1981. The company (i.e., the name Goldmund, and the right to produce and sell the products) was then sold to our former distributor.

Although we were a small company, we had the opportunity to create and develop new concepts, new techniques in high-end audio, thanks to the use of specialized consultants, with computing facilities.

We first introduced the Goldmund T-3 radial tone arm. This unit was optoelectronically controlled, so as to ensure an almost perfect position of the cartridge during the record play. A turntable was introduced the following year, called the Goldmund Studio, combining for the first time the direct-drive principle with the floating subchassis technique. In addition, the use of a high-inertia platter, machined in methacrylate and lead, allowed a very low level of resonances. The last Archi- tecture & Physique Appliquée product was the Classique preamplifier, with very high slew rate, 75-volt power supply, and very short signal path.

After the company's closing, in 1981 (a short life, due to our lack of commercial talents), different products continued to be marketed under the name Goldmund that were not designed by my team any longer (but the brand Archi- tecture & Physique Appliquée remained

my property and was thus removed),

We were happy to find that some well-known "audio critics" rated our arm and turntable at the "state-of-the-art" level (in The Absolute Sound). I still don't know what were the comments and evaluations of our products in the rest of the audio press in the U.S.A. (not being easi-

ly available in France at the time)....

Although the tests in TAS didn't seem to be conducted in a very scientific way, we were, of course, glad to see that our methodical research and calculations were confirmed by an independent reviewer (that is, independent of the company at least), even subjectively...

I would like to add a suggestion to

this letter.

I think all your readers are satisfied

with your well-informed, accurate, and reliable articles. But some, as I do, may think that too much space is dedicated to

contradict and debate with the "sub-

jectivist" brigade. You can assume that

the vast majority of your readers are aware of what a fair, reliable test or comparison is and, more important, are not

that much interested in knowing exactly

when and where Mr. X, or Y, was wrong

in his hype and unscientific evaluations.

What a good, competent reviewer can do is to use his knowledge, laboratory, and experience with audio products to go straight to the point, and extract the valuable information out of the facts. This is, in my opinion, what your readers find most instructive in The Audio Critic. Why should you waste time arguing with astrologers and fortune-tellers (so to speak)?

I hope these few lines will be of some use to you and your team... Con-

gratulations on your work.

Yours faithfully, Michel Levy Paris, France

So—how should we deal with the

witch doctors, charlatans, snake-oil peddlers, Enid Lumleys, frauds, "other"

journals, astrologers, and fortune-tellers

of the audio world (to borrow our correspondents' terminology)? Should we devastate them, in the words of Chris

Walker and with the concurrence of Ed-

ward Doyle and even Prof. Pohlmann (further above)? Should we avoid all con-

frontation with them because it's unseem-

ly, as Dr. Overman and C.K. Vissanji ap-

pear to believe? Or should we just give

up on them and attend to more important

matters, letting them slowly but inevitably self-destruct, as Terry McCarthy and Michel Levy seem to think is wisest?

I think the underlying question here is just how influential and effective this untutored, antiscientific element has become in audio, and I think the answer is: very. Go to your local audio salon and

find out where the pimply-faced "audio

consultant" in the Metallica T-shirt gets his strong opinions. From Professors Stanley Lipshitz and Richard Greiner? No way! From Harry Pearson, Robert Harley, and other loudmouthed tweako

"authorities." Those strong opinions are then imparted to that nice retired dentist with $20,000 to spend on a new system, who probably has never heard of Lipshitz and Greiner—or, if he has, thinks they represent just another partisan opinion—

and who will then impart them to all his well-heeled friends. He is the key player in this situation.

You're wrong, Messrs. McCarthy,

Vissanji, and Levy; ten years and more

could go by before that dentist and his

friends realize—if they ever do—just how

stupid and ridiculous those tweako opinions are, unless I and my colleagues are constantly in their face with the documented, tweak-humiliating truth. And even then...

My decision is to heed the advice of Ken Pohlmann. In the immortal words of William Blake,

I will not cease from mental fight,

Nor shall my sword sleep in my hand

until I see the entire tweako cultist scene

discredited in the eyes of the majority of audiophiles, not just the professionals and academics.

—Ed.

The Audio Critic:

As a new subscriber, I am somewhat

disappointed in your reviews. Before I

mention specifics, let me state that I am not an "expert, tweak, geek," or whatever term one chooses to use. I do have minimal knowledge about electronics and speaker systems.

I would appreciate your response to

the following, which concerns your Hsu Research HRSW10 review in Issue No.

19:

1. You state, "The enclosure is...

acoustically inert...." Olsher (Stereo-

phile, March 1993) says, "...the SW10

was alive to the touch...a nut driver I'd left on top of the enclosure started to

dance in rhythm to the signal. It felt as if

THE AUDIO CRITIC

pdf 10

the whole enclosure was readying itself for launch."

You say, "The distortion may have been slightly higher than with the Velodyne ULD-15 Series II at equal

SPLs...." Keele (Audio, November 1992)

has THD graphs which show a maximum distortion of 2% in the 20 Hz band of the Velodyne, but the Hsu graph shows much higher levels (up to 15%).

The above concern is related to subwoofers for one reason: I want to buy a good one; it's not that I'm picking on Hsu (or anyone, for that matter).

I do appreciate your straight talk about the "pseudohigh-enders" who claim to hear what most others cannot.

I look forward to your response.

Sincerely, James R. Story Miami, FL

/ am genuinely distressed about

your initial disappointment as a new subscriber, even though your negative reaction represents about one in a thousand. It may be, however, that you don't read our reviews attentively enough—nor the reviews in Stereophile and Audio.

I didn't write that "the enclosure

is...acoustically inert...." Ellipsis has its

limits. I wrote that "the enclosure is a cheap but extremely strong and acous-

tically inert paper tube...." The paper

tube is indeed acoustically inert. Olsher himself (not that I have the slightest respect for him as an audio reviewer) wrote, "The weak spots are the end

caps... .A tube readily resists radial pres-

sure...," etc. So we have no momentous disagreements about the tube. About the

end caps Olsher is wrong, as usual. The

end caps are quite small, stiff, and essentially mode-free; they are in a sense

the "braces" of the structure. The problem is that the entire structure is very light, so that high-energy axial excitation (i.e., long-excursion woofing) makes it

"dance" a bit—as a unit. This is analogous to the recoil of a lightweight weapon using heavy ammunition. If the enclosure were bolted to a concrete floor, the effect would be minimized. Even Olsher (there I go again) refers to this "grounding " consideration. The sonic consequences are negligible, in any event.

As for Keele (for whom I have the highest respect), look again at his words and pictures. First of all, he compares the Hsu HRSW10 with the Velodyne F1500, not the ULD-15 Series 11. Second-

ISSUE NO. 20 • LATE SUMMER 1993

ly, he points out that "the maximum levels [of the F-1500] were set by the action of the system's limiter circuits." For example, at 16 Hz and 20 Hz, the F-1500

cuts off at 88 dB SPL and 2% distortion. At that level and those frequencies, the Hsu is barely higher in THD. What I wrote does not contradict Keele, even if you assume that the ULD-15 Series II and the F-1500 have absolutely identical distortion characteristics, which is not the case.

My recommendation: If price is no object, or of relatively small importance, get a Velodyne—because it's closer to perfection. If price does matter, however, then get a Hsu (get two Hsus, that is) and you'll be just as happy.

—Ed.

The Audio Critic:

It was with some difficulty that I waded through the rarified atmosphere of "...the longest crank letter ever..." in Issue No. 18. As I struggled, it occurred to me that, for a follow-up, what is needed is the shortest crank letter ever.

Much like Ye Ed., I thought I detected a slight difference on some recordings when inverting polarity. Rather than being confused by a bunch of papers on psychoacoustics, I elected to conduct my own experiment, starting a the point where sound terminates and then working backwards from there.

1. A good flat mike was placed at listening position (only place that counts).

2. Room had already been neutralized with my version of a poor man's anechoic chamber, so received sound was a virtual sonic copy of speaker output.

3. Speaker geometry was optimized for best soundstage and flattest response.

4. A test signal was applied through a switchable inversion stage to line amp and was found, at speaker input, to be a precise mirror image (equal shape and size) when inverted. Positive-going pulse was identified as a speaker push and negative as a pull.

5. Test signals which appeared at mike were not precise mirror images when inverted but indicated more compression in the negative direction than the positive, the effect becoming more noticeable as drive was increased.

6. Newly built and hopefully more linear speakers were deployed, and inversion differences essentially disappeared—distortion increased equally as

overload was approached.

In the 8 years I've lived with this system, only one person has heard an inversion difference. His auditory senses obviously were quite acute, as he heard a difference when I only pretended to invert.

Here on the low plains—as opposed to the hill country and University of Texas—we refer to it as the "cow chip effect" and let the chips fall where they may.

Donald F. Scott Houston, TX

1. Ye Ed. used to be Gordon Holt's way of referring to himself, if I remember correctly; I try eschew such cutesyisms. (I'm not nearly as cute, cuddly, and pixieish in my autumn years as Gordon.)

2. Cow chip effect vs. B.S.—isn't that sort of analogous to the politically (not theologically) supercorrect way of referring to the Deity as She? We must

not be sexist, or gender-insensitive, even when it comes to bovine excreta.

3. What you say about polarity in-

version is quite consistent with Prof Richard Greiner's highly researched

paper on the subject at the 91st AES Con-

vention (October 1991) in New York.

—Ed.

The Audio Critic:

I am...a loudspeaker hobbyist. That

means I design and build my own systems and basically have a hell of a good time tinkering around with them. I agree that the loudspeaker is the most important

part of the audio chain....

...I received some literature from

Martin-Logan the other day. Nice-

looking speakers. But, I found something in their specifications that tickled me and that I thought you might appreciate (see enclosed).

[The Martin-Logan literature in

question claims the following specifica-

tion for the 12" woofer used in two of their speaker systems: "Woofer speed @ 50 Hz: 6.3 ms (comparable to most 8" drivers)."—Ed.]

I'm no physics major, but isn't speed measured in distance divided by time? Well, they got a time; I wonder what the distance was? I can see myself

asking the cop who pulled me over how

fast I was going, and he says, "Sir, you

were going 3 seconds."

There's another thing; they say that this woofer speed is "comparable to most

8" drivers." I looked through all my driv-

pdf 11

er catalogs and couldn't find one 8" driv er with a 6.3 ms speed rating. Go

figure....

Sincerely, Steven A. Crosby APO AE

A "fast woofer" is one of the techno-

illiteracies of the high-end audio ghetto.

As I've said more than a few times, if a

woofer were fast, it would be a tweeter.

Tweeters have a fast rise time, another way of saying extended bandwidth. Woofers don't have that and don't need it.

Woofers need to be well-damped, meaning that they must shut up quickly after

the signal stops. I think that's what the tweaks really mean by "fast" in this context.

That Martin-Logan spec is probably some kind of settling time after some kind of specified pulse excitation—I'm only guessing. The amplitude information is missing, as you point out. Martin-Logan is known to me as a serious, engineeringoriented loudspeaker company, not a tweako cultist operation, but in this case there appears to be a bit of terminological pandering to the audio-salon cowboys. The good news is that the latest

Martin-Logan literature I picked up at

the Summer CES no longer includes that

questionable spec. Maybe others like you got to them.

—Ed.

The Audio Critic:

...Concerning the ACI G3 review in

Issue No. 19: "floor bounce" is the am plitude variation with frequency due to different path lengths of the direct radia tion from the woofer and the reflected ra diation from the floor. Frequencies af fected vary with the height of the woofer and the listener's location. The "Allison Effect" is a variation in woofer power output due to interference with reflections from nearby room boundaries. The fre quencies affected depend on wooferto boundary path length. These two effects are not the same.

Sincerely, Robert T. Kuntz Medford, OR

The "Allison Effect" was discussed in detail by Roy Allison himself in his interview with David Ranada (Issue No. 18,

pp. 54-55), so I'm not exactly a stranger

to the concept. I plead guilty to having referred to it somewhat sloppily. Anyway, Roy doesn't like the woofer to be mounted high up—right?—and in the ACI G3 it isn't. That's basically what I was trying to say; your commentary is more precise.

—Ed.

The Audio Critic:

So far I've only read two issues of

your magazine. It has confused me, an gered me, made me think, and thoroughly

delighted me. Thank you....

.. .Can you please explain to me why

the highend mags consider the Toslink output inadequate? I Use it to clone CDs to DAT and wonder if I'm compromising quality.

Thanks for entertaining and en

lightening me.

Sincerely, Patrick T. Chamberlain Albuquerque, NM

The theoretical argument against Toslink is that the bandwidth of the plastic fiber-optic interface may not be quite

adequate, resulting in imprecise recovery

of the clock and consequent jitter. But, if there is jitter, it will inevitably show up in the THD + N versus frequency measure-

ments at the higher frequencies, and I have never seen a difference in that test

between Toslink and coax. Furthermore, in digital-to-digital copying such as you

do, jitter is a total nonissue. So relax and stop worrying. Those 1's and 0's are not so fragile.

—Ed.

The Audio Critic:

...In Issue No. 18 you discuss line

level preamps. On page 18 you discuss capacitors in the signal path, with a refer ence to the Jung/Marsh articles in Audio

magazine. I have enclosed a copy of a

paper I wrote, entitled "Ceramic Ca pacitors," written in response to the Jung/ Marsh articles. Jung & Marsh incorrectly assumed, based on the experiences with

one specific type of ceramic capacitor (X7R dielectric), that all ceramic ca pacitors were inferior. My paper shows that there are several distinctly different types of ceramic capacitors, and only some of them are inferior. The COG/NPO dielectric is superior. A later paper by Jung takes a much more accurate view of ceramic capacitors.

Your discussion of capacitors com pares the use of electrolytic capacitors in speaker crossovers with their use in preamps, where "...the voltage swings are much smaller and the loads larger by at least three orders of magnitude." Your point is that the smaller voltage swings and higherimpedance loads will mean that capacitor "...nonlinearities in the range of human hearing should not be measurable." If you look at the THD graph in my paper, you will see that THD of almost 3% is possible with the Y5V dielectric, with a load of 1 kΩ the high pass filter. Even at a substantially higher impedance load, distortion caused by the Y5V dielectric would still be very mea surable.

I hope nobody would be stupid

enough to use a Y5V ceramic capacitor

in the frequencydetermining network of

an equalizer or electronic crossover,

where it would be working in the audible

frequency range. However, there may be numerous products that do use inferior types of ceramic capacitors for the op amp feedback loops and/or frequency

compensation networks....

Sincerely, John W. Hardy President The John Hardy Company Evanston, IL

David Rich, who wrote that sidebar on "Capacitors in the Signal Path, " says he does not disagree with you, and I certainly do not. (But all dielectrics are guilty until proven innocent, aren' they?) In any event, designers of high-quality audio equipment almost invariably specify film capacitors for the smaller values at all points in the circuit where distortion could be an issue.

—Ed.

THE AUDIO CRITIC

pdf 12

The Tweaks vs. the Pros:

Is It a Bona Fide Debate

Between Two Points of View?

By Peter Aczel

Editor and Publisher

The audio world has been conditioned to see this subject in a

strangely distorted perspective. It appears that even some level-

headed audiophiles could benefit from a bit of clarification.

When a controversy goes on too long, the issues

tend to become distorted, sometimes beyond recognition.

Originally, the hotly debated question in audio was

whether or not good measurements guaranteed good

sound. That was a legitimate debate, especially in those early days when measurement protocols were quite skimpy and the psychoacoustic correlations unexplored or unproven. Over the years, clouded by the agenda of the ultrahigh-end audio community, the debate degenerated

into I-know-I-can-hear-it vs. prove-to-me-that-you-canhear-it. The sad thing is that the unending back-and-forth on the constantly shifting ground of this controversy has left many audiophiles with the impression that a fundamental clash of philosophies was taking place, the audio

world's equivalent of capitalism vs. socialism, religion vs. atheism, Republicans vs. Democrats, protectionism vs. free trade, batting pitchers vs. designated hitters, etc., etc. That is an enormous misperception. The way the lines are drawn today, the debate doesn't have two arguable sides. It's more like laetrile vs. the AMA or the Ku Klux Klan vs. civil rights.

Consider the typical equipment reviewer for one of the "subjective" audio journals. He receives a new amplifier, plugs it into his system, listens to it for a while, and then declares that it has better soundstaging but a less liquid upper midrange than the amplifier that was in the system last week. No side-by-side comparison at matched levels, no attempt at blind listening, just total confidence in his golden ears, his exquisite judgment,

and his perfect aural memory. Isn't that the height of nar-

cissistic presumption (not to mention psychoacoustic

illiteracy)? And isn't it the height of mindless credulity for an audiophile to follow such a reviewer's advice?

There's no plausible side-taking in a two-sided philo-

sophical controversy there. That reviewer is simply an unprofessional slob who can't be bothered with time-

ISSUE NO. 20 • LATE SUMMER 1993

consuming homework, and the audiophile who relies on him for guidance is an undiscriminating innocent. (Of course, the mystic rituals of high-end audio have always attracted the natural-born cultist, and cultists are prone to believe anything, on any subject. To bring up an extreme example—who would have thought that the third-rate con man, child molester, and dilettante rock 'n' roller who called himself David Koresh would be believable as the Son of God to a group of outwardly nonpsychotic persons? Next to that, the tweakiest audio reviewer is a paragon of credibility.)

Please note that I am not minimizing the importance of listening. Audio is about listening, and ultimately every piece of audio equipment stands or falls on its performance in the listening room. Listening is an allimportant part of equipment evaluation but it must be a great deal more structured and disciplined than the totally chaotic, self-indulgent, freeform exercise it has become in tweako reviewer circles. Yes, you can enjoy music without critically listening for audio quality—just go with the flow, man, etc.—but no, you can't just dip into amplifier A on Tuesday and amplifier B on Wednesday like a restaurant reviewer and then declare A to be superior to B. The ground rules of meaningful listening tests were explained in considerable detail in Issue No. 16, so I don't intend to rehash them here; what I want to convey in this discussion is the absence of even marginally defensible arguments on the tweaks' side of the debate—it is in effect a nondebate, with all the informed opinion on the other side. Indeed, it is an essential requirement for obtaining membership in the tweaks' circle to have no university degrees in engineering or physics and to have no professional status in audio anywhere outside the high-end manufacturing/retailing/writing ghetto. If there are any exceptions to that, I'm not aware of them.

Let us examine some of the favorite tenets of the

pdf 13

tweaks and see whether a scientifically respectable twosided argument can be occasioned by any of them.

Listening for differences.

Maybe we should start with the basic shibboleth that takes the form of "why don't you just listen for yourself and you'll hear the huge difference between the Mark Levinson and the Bryston" (to pick an ultrahighend and a merely high-end brand at random). You can listen for yourself till the cows come home and you won't be able to reach a valid conclusion unless (1) you

can readily switch between the two units side by side, as quickly or slowly as you wish, (2) their identities are concealed from you when you try to determine from their sound which is which, and (3) their levels are matched within ±0.1 dB. All psychoacousticians, psychophysicists, statisticians, and credentialed audio electronics authorities agree with that statement; only the Atkinson/Harley crowd opposes it with all kinds of untutored aesthetical, psychological, and philosophical babble without proof. I don't consider it to be an intellectually respectable debate because there aren't respectable practitioners on both sides of it. Casual, sequential, "open-loop" listening evaluations are pretty close to worthless; nobody with serious credentials defends them.

That pesky level matching within ±0.1 dB is a key issue. I have found that tweako magazine reviewers as well as private experimenters tend not to do it even when they pay lip service to it; often they lie about having done it because it is too damn time-consuming, boring, and irritating to do accurately. You need a digital voltmeter with dB display, a stereo attenuator with coarse and fine adjustment, a reliable sine-wave signal source, and lots of patience—because four channels must be matched in a stereo comparison, sometimes with temperamental balance controls, etc., in the signal path. Not for the short-

attention-span, instant-gratification, yeah-that's-it audiophile. But it must be done without fail, otherwise all bets are off. A mismatch of 0.3 dB is definitely audible and

will most probably be perceived as a difference in quality

rather than level. (An easily identifiable level difference is usually closer to 1 dB.) As soon as A sounds even slightly different from B, audiophiles will declare one to be vastly superior to the other, and that's how the B.S. starts.

My most shattering experience in audio was the first time I bothered to match levels accurately. The two preamps I was testing began to sound exactly the same, and my audiophile belief system crumbled. (Yes, they still would have sounded different if they had differed by more than 0.2 or 0.3 dB in frequency response, but they were both dead flat, alas.) It has become my firm conviction that level matching is the big stumbling block that prevents rational audiophiles from leaving the tweako camp.

Let me hasten to add (although I shouldn't really

have to) that even under properly controlled listening conditions numerous audio components will sound different and therefore require subjective evaluation. Those who are able to read The Audio Critic without moving their lips know very well that the "everything sounds the same" label the various tweako journals try to stick to our audio philosophy is a malicious misrepresentation. What we insist on is that there are no unexplainable sonic differences, no mysterious "X factor" that golden-eared high-end designers dial into their creations. Audible differences are due to frequency response, distortion, noise, impedance effects, and so forth—in other words, to quan-

tifiable phenomena. In most cases the quantification is easy, in some not so easy, but the mechanism whereby the audible difference occurs is never inexplicable. Once again, try to find a genuinely credentialed authority who disagrees with that.

The glowing bulb fallacy.

It really bugs me that so many audiophiles still insist that "tubes sound better." Such nonsense! At the risk of sounding repetitious, I challenge all you tube freaks to find someone with a university graduate degree in electronics who is of the opinion that there are tube circuits for audio applications whose ouput, with any given input, cannot be totally duplicated by a solid-state circuit. Come on, guys, your vacuum-tube gurus and designer heroes are all dilettantes—former audio salesmen, sales managers, tweako audiophiles turned manufacturers, anything but credentialed professionals in electronics. Show me a published IEEE or AES or other scientific paper

documenting the superiority of vacuum tubes over properly operated, modern solid-state devices in audio circuits. There aren't any. Get real, guys.

Yes, vacuum tubes are great for broadcasting appli-

cations, outputting kilowatts of RF power. They're also good for generating various pleasant, "musical" distortions in guitar amplifiers, compressors, equalizers, etc., but of course solid-state circuits can be built to mimic those same, nice, old-fashioned distortions without requiring perishable parts made in disintegrating Eastern European countries. Some audiophiles love that kind of distortion in their main power amplifier and preamplifier as well, but then why not get an Aphex Aural Exciter or some other external grunge box? That you can at least turn off. (See page 55 of Issue No. 16 to understand what a tube power amplifier with a high output impedance— i.e., low damping factor—can do to the frequency response at the speaker terminals. Sure you can hear a 2 dB range of response fluctuations; you're even allowed to love it; but I can give you the same thing with a 10-watt 1-ohm series resistor.)

Best-case scenario: somebody comes up with a tube amplifier or preamplifier that does everything the best solid-state units can do, except for an order of magnitude higher distortion—mostly second harmonic—plus

THE AUDIO CRITIC

pdf 14

a higher noise floor and significantly shorter mean time between failures. That's the absolute best you can hope for, so why bother?

The magic cable fallacy.

At the Summer CES in Chicago, Ray Kimber of Kimber Kable walked around with a length of speaker cable (I think it was about four feet long), telling everybody—and relishing the shock effect—that this latestand-greatest Kimber product would be selling for $15,000 the pair. I asked him whether it sounded better than no cable at all, with the amplifier terminals soldered directly to the speaker terminals—you could do that for a few dollars with, say, two inches of copper bar per terminal—and he said no, how could it, but it sounds just as good! Then I asked him whether he believed he could hear the difference between his magic cable and some kind of cheap cable I proposed to cobble together, having exactly the same resistance, same inductance, and same capacitance as his. He said yes, of course, 100% of the time. I challenged him to a double-blind listening test to prove that, and he accepted—but didn't stick around to complete the arrangements. (Don't hold your breath, dear reader.)

My point is that any cable, whether it costs $1.50 or $15,000, is an RLC circuit and will behave accordingly. Whatever effect the cable has on the sound, that effect will be due exclusively to the R, the L, and the C of the cable, interacting with the output impedance of the amplifier and the impedance characteristics of the speaker. To make R, L, and C as small as possible—and thus have minimal effect—costs some money but not many hundreds, and certainly not thousands, of dollars. Superexpensive cable does absolutely nothing for you. I explored this subject in some detail in Issue No. 16 and cited as my main supporting authority the writings of Richard A. Greiner, Ph.D., an E.E. professor at the University of Wisconsin. Since then another professional engineer, Fred E. Davis, has added his voice to those of the advocates of science and reason on this subject, in the form of heavily documented articles in the Journal of the

Audio Engineering Society (June 1991) and Audio (July

1993). He basically comes out in favor of reasonably low

R and the lowest practicable L, and observes that the dif-

ferences are small in any event. The voices on the tweako side of the issue, now as before, belong to lightweights without any comparable credentials. Again, no genuine debate.

The antidigital fallacy.

Digital audio has brought us flatter frequency response, deeper bass, wider dynamic range, lower THD, lower noise floor, safer storage, and greater editability than any other technology in the history of sound reproduction. It has every scientific reason to sound better than analog, and it does—the possible exception being

ISSUE NO. 20 • LATE SUMMER 1993

30-ips analog tape with Dolby SR, which is capable of sounding equally good (with some qualifications), but which the tweaks aren't even talking about. They talk about vinyl, for crying out loud; they say digital just doesn't have the same airiness, smoothness, front-toback depth, dimensionality, tonal gradations, etc., etc. This is truly sickening drivel, without any foundation in logical thinking or accurate hands-on observation.

Vinyl is not a primary medium; it is nearly always a transfer from tape, sometimes even digital tape, except for the very few direct-to-disc recordings. The process of transferring tape-recorded material to vinyl entails measurable losses and distortions; reading the vinyl groove with a pickup entails further measurable losses and distortions, not to mention mechanical ticks, pops, and swishes. The tweaks appear to like the results of this

flawed process, especially the added L-R component introduced by the insufficiently orthogonal motional characteristics of the cutter and pickup. That's your extra airiness and depth, tweaks—and it isn't on the analog master tape! Nor is the lovely "smoothing" effect of the vinyl noise. At the very least, the comparison of analog vs. digital should be master tape vs. master tape—but it never is because the digitophobic cultists don't know any better. (Actually, the digital recording in the comparison could be a CD or an R-DAT because the codes are exactly the same as on the master tape, but the cultists are hazy on that too.)

Once again, where are the authorities in support of

the antidigital arguments? At the tweako magazines and the tweako stores, that's where. And where are their credentials as authorities? Nowhere. Herbert von Karajan hailed the advent of digital recording with the remark that "all else is gaslight." But Harry Pearson didn't like it, nor did Michael Fremer. And now the great "digital expert" Robert Harley also travels cheerfuly with the analog-is-still-best crowd, although it's rumored he didn't even own any vinyl LPs back in 1989. Pearson, Fremer, Harley—versus Karajan? Versus John Eargle, Stanley Lipshitz, etc.? You call that a debate? Even the illustrious Edward Rothstein of The New York Times has been heavily qualifying his unconvincing antidigital quibbles lately. I think the more intelligent analog diehards are in retreat.

Making the l's and 0's more 1-ish and 0-ish.

The same element that bashes digital and extols an-

alog seems intent on "improving" digital with nonsense products that you glue, paint, spray, rub, clamp, etc., on your CDs. This is so primitively unscientific that you can't even talk about a phony debate; here we are in witch-doctor territory. No double-blind listening tests have ever revealed improvements with theses devices; no authority with serious credentials has ever endorsed them. A CD stores numbers; you can either read a number or you can't—no massaging will make it "better."

Why not address problems that need solving? •

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A New Look at

Medium- and High-Priced

Power Amplifiers

By David A. Rich, Ph.D.

Contributing Technical Editor

This will be an ongoing survey stretching over a number of issues. Seven units are reviewed in this first installment, which introduces a new method of measuring amplifier/speaker interaction.

Editor's Note: Just like the CD player and preamplifier

surveys by Dr. Rich, some of the writing that follows here is a bit more technical than many readers of general audio magazines may be prepared for. The overall evaluations and conclusions are loud and clear to anyone

who has ever considered purchasing an amplifier, but some of the engineering explanations may be tough going for nontechies. I am not totally happy about that

but I have not edited out any of the technical material because I feel that it should be in print and available for

reference. Amplifiers have been the subject of incredibly stupid, ignorant, misleading writing in several publications that ought to know better, and we definitely need to add what we can to the small storehouse of authoritative

amplifier information accessible to audiophiles.

* * *

Introduction.

The design of a power amp is a nontrivial matter. A

power amplifier is required to produce over 100 volts

peak to peak. Low-impedance loads may demand peak

currents in excess of 50 amps. The amplifier must be stable into an unknown load, which, depending on the speaker's design, can have a range of close to two orders of magnitude. The phase angle of the load can range from an almost pure capacitance to an almost pure inductance and everything in between. The amplifier must not blow up into an open circuit (when no speaker is connected) or a short circuit or when its inputs are hotsocketed or when the input level drives it into clipping.

If you had told me 20 years ago that commercially

manufacturable power amplifiers would be designed to

do all of the above and produce maximum distortion lev-

els of 50 parts in a million, I would not have believed it.

If anybody could have pulled off such a feat, I would have been sure the audio community would declare the

designer a genius and his amp would be a most coveted

item. As we will see below, such amps now exist, but their designers are not hailed; no, they are actually scorned by the high-end community. Anybody can make an amp that measures good, we are told. Instead, high-

end reviewers and dealers will tell you a good-sounding

amp is a work of art, not science. Do not worry about the numbers; they do not matter, you will be told. Do not ex-

pect the amplifier to be reliable, for this is also in conflict

with good sound, they say. Well, I do not believe a word of this. In the reviews below and in coming issues I will recommend the best-built and best-performing amplifier. Amplifiers that come close but cost a lot less will also be recommended.

The sound, or the lack of it.

We still get letters asking why I do not discuss the sound of the equipment in my reviews. I do not know how The Audio Critic can be any clearer on this issue. If a piece of electronics has flat frequency response, vanishingly small static and dynamic nonlinearities, a high enough input impedance and low enough output im-

pedance, a noise level below audibility, and high enough

channel separation, then it is not going to have a sound. ABX testing confirms this. That is not to say all amplifiers sound the same. Clearly an amplifier can have insufficient voltage- and current-drive capabilities for a given loudspeaker, and that is going to be audible. Our test regime is designed to identify wimpy amplifiers.

Amplifiers are also going to sound different if they do

not satisfy the above conditions.

Take the much-praised Jadis JA-200 monoblock

power amplifier, which sold for $17,500 the pair (four

chassis, actually) the last time I looked. Here is a vacuum-tube amplifier with high static distortion, an inband slew-rate limitation, marginal stability, and high output impedance (low damping factor). Now this amplifier is

THE AUDIO CRITIC

pdf 16

going to sound different. The problem is that audio re-

viewers often confuse different with better. The Jadis is in effect a very expensive equalizer rather than a real amplifier. The Carver "t-mod" was basically an elegant experiment to prove the above statement and others like

it. Instead of ending the discussion, the t-mod resulted in

an attempt by the high-end community to discredit and destroy Mr. Carver. Despite all of the available evidence, the majority of audiophiles continue to want to believe. In what other field could the following quote, from a Bascom King review of the Jadis amplifier {The Absolute Sound, Issue 41, Spring 1986), be taken seriously?

"So why do these amplifiers sound so good? Now my job gets tough. The bottom line: I don't really know. The only really good measurement is of its harmonic structure. Output impedance and amount of harmonic and IM distortion are OK, but, the gross slewing or reduced high frequency power output is bad. The truth is that the measurements most of us make are not very relevant to the sound of circuits and I've spent a good part of my career looking for ones that do with little success so far."

Now, if this makes sense to you, you might as well

stop reading this article, go out, and buy yourself a megabuck tube amplifier/equalizer. If the above quote does not make sense, then stick around—you are going to pay a lot less for an amplifier, and it is going to sound better than the Jadis. I hope you now understand why I do not need to characterize the sound of the individual amplifiers reviewed below. They all (except the Michael Yee special) meet the above electrical criteria for inaudible differences. We confirmed this with a series of ABX tests that included all of the amplifiers. (All except the Michael Yee unit, which blew up—twice! Remember what the dealer told you: if it sounds good it's going to be tem-

peramental, just like an Italian sports car....)

Why do they call it a power amp?

Let's start our technical discussion with the muchdiscussed fact that power output is not the parameter to characterize the drive performance of an amplifier. All commercial amplifiers are voltage-drive. (Papers on current-drive amplifiers have been presented in the AES Journal.) Ohm's law requires that when the amplifier imposes a voltage across the load, the amplifier must also be able to source the required current. For the case of a resistive load, a one-to-one correspondence exists between the voltage output of the amplifier, the current flow of the amplifier, and the power dissipated by the load. When an amplifier is connected to a purely reactive load, the voltage and current waveforms are displaced by 90°. Under these conditions, no power is dissipated by the load, but the amplifier must still drive the load with the appropriate voltage and it must source and sink the current from the load. Indeed, the power being dissipated by the amplifier itself actually increases when driving re-

ISSUE NO. 20 • LATE SUMMER 1993

active loads [Benjamin 1992]. It is thus more appropriate to characterize the amplifier in terms of the voltage it can supply across a variety of load conditions. Both the magnitude of the impedance of the load and the phase angle of the impedance need to be varied.

When an amplifier is required to source (or sink) a significant amount of current, losses in the power-supply transformer and the output transistors reduce the amount of voltage which can be imposed across the load. An amplifier designer is presented with an interesting tradeoff. For a given size and cost, a transformer can be specified which supplies a large unloaded voltage but which has a large internal resistive loss. Conversely, a transformer can be chosen with a lower unloaded voltage but a smaller internal resistive loss. When driving a highimpedance resistive load, the larger voltage available from the first kind of transformer will allow more power to be delivered to the load. When the load is reduced in value, the transformer losses become significant and the power-supply voltage (and hence the available output voltage) decreases, thus less power can be delivered to the load. This is where the second kind of transformer becomes more appropriate. Although its unloaded voltage is lower, its voltage under these load conditions is higher, and the power to the load is thus also higher.

Even if a lossless transformer existed, current output would be limited by output transistor losses. Adding additional transistors in parallel reduces these losses and allows the amplifier to produce a more constant voltage output as the load is varied. In addition to more output transistors, more heat sinks must be added to the amplifier if the amplifier is to drive a low-impedance load. This is because amplifiers have a finite conversion efficiency. Not all the power reaches the load. Assuming a resistive load and a lossless output device, a class A amplifier is only 25% efficient! An ideal class B amplifier is only 78.6% efficient. Since more power is being transferred to the low-impedance resistive load, more power is being dissipated by the amplifier and more heat must be dissipated. (Remember, reactive loads can make this situation worse.) An additional factor to be considered is the size of the primary filter capacitors. The filter capacitors hold the power rails up in between conduction cycles of the diode bridge connected to the power transformer. The capacitors must be sized large enough so that the power supply does not sag under maximum current draw. An amplifier that can supply a ±140 V peak-to-peak swing into a 1-ohm load continuously is putting 2400 W into a resistive load (into 8 ohms only 300 W is being delivered to the load). The Krell KSA300S is claimed to be such an amplifier; it weighs 185 pounds, has a 5 kVA transformer, 0.27 F of supply capacitance, and costs $8500. Now, if you are driving a pair of 1-ohm loads continuously in stereo, you need this amp. If not, this is clearly overkill. That does not mean you should not spend the money; just look at the expense

pdf 17

in the same light as spending $80,000 for a sports car that can go 180 mph.

Measurements and current limiters.

Even if a power amp cannot source high values of current on a continuous basis—because of transformer losses, inadequate heat-sink sizing, and high outputdevice drops (leading to rapid internal heating)—it may be able to do so for a short period of time. This is accomplished by oversizing the main filter capacitors so that they keep the power rails up for a short period of time, even though the losses in the transformer would prevent the rail from being held at a high voltage continuously. Output-current-limiting circuits or fuses limit the time during which the output devices source current beyond the maximum allowed under continuous operation. These same elements prevent the amplifier from being damaged during fault conditions, such as a short across the amplifier. That extra headroom available for a short duration is called dynamic power. The Audio Critic is the first magazine to use a new method for assessing dynamic power output, called The PowerCube. The PowerCube, a software-driven automated instrument with a

PC front end, measures the maximum voltage the amplifier can deliver to the load at 1% distortion for a duration

of 20 ms at 1 kHz. The loads have impedance magnitudes

of 8, 4, 2, and 1 ohm, and phase angles of -60°, -30°, 0°, +30°, and +60°. The graphic output of the instrument

shows the 20 data points connected to form a more or

less cubelike polyhedron, which illustrates at a glance the true dynamic performance of the amplifier. The test takes only a few minutes per channel. Under ideal conditions the voltage sourced by the amplifier should be a constant, and The PowerCube should look like Figure 1. We haven't seen one like that so far. A real amplifier, even a very good one, is going to exhibit some tilt in the cube, as shown in Figure 2. The extent of the tilt depends principally on the primary capacitor reservoir size, the losses across the output devices, and the action of the current limiter if it is present.

A brief detour into the operation of the current limiter is required at this point. The current limiter must consider the voltage across the device, the current flowing in the device, the temperature of the device, and the amount of time that a high-current condition has existed. Ideally

A/D converters would transmit this information to a mi-

crocontroller, which would compare the operating conditions to a template of the SOA (safe operating area) con-

ditions for the output devices and determine if the output current should be limited or if the amplifier should be

shut down. Krell literature hints at such an approach in

their very expensive amplifiers. The next best thing is to use analog circuitry to calculate the instantaneous power dissipated by the devices. Additional circuits integrate this value and then determine if it exceeds the SOA of the devices [Didden 1983]. In most amplifiers a much

simpler one-transistor circuit is used to limit the current. The base-emitter junction of the transistor is placed across resistors in series with the output devices. When the current in these resistors becomes large enough, the transistor is turned on. The collector of the transistor is connected to the base of the output device or sometimes to an earlier part of the circuit. When the protection transistor is on, current is diverted away from the base of the output device, reducing the current the output device can supply. Some additional circuitry may be included to add a time delay to the circuit's action or suppress oscillations that could occur when the limiter circuit is tripped

[Leach 1980]. Properly designed, the circuit can work reasonably well, but several researchers have noted major problems with the circuit if it is not optimally designed [Holman 1981], [Baxandall 1988], [Fairwood and Reed

1991]. When the current limiter is not designed properly, it will typically limit current prematurely or will limit when the load is reactive. Although it is possible for a poorly designed current limiter to trip too early on reactive loads under some conditions, it is necessary for the current limiter to activate at lower current levels when the amplifier is driving a reactive load [Benjamin 1993] if the output stage is underdesigned.

The PowerCube helps us assess the performance of the current limiter from the tilt of the cube and from a loss of voltage into reactive loads. There will be a ridge through the center line of the cube and the top surface of

the cube will bend downwards away from that center line if the current limiter is malfunctioning (Figure 4). Another thing The PowerCube can tell us is how stable the amplifier is into reactive loads. If the cube has a missing corner (Figure 5), it is likely that the amplifier is unstable or marginally stable into the load. When unstable, the amplifier distorts at a lower power level, or oscillations start to occur, limiting power output. You may ask if it is important for an amplifier to work into a 2- or 1-ohm load. Surprisingly, the answer is that many popular loudspeakers can present difficult loads that require this [Vanderkooy and Lipshitz 1986], [Otala 1987], [Baxandall

1988], [Fairwood 1991], [Benjamin 1992]. Note that The

PowerCube and the theoretical work behind it are relatively recent developments. An amplifier which fails the PowerCube test is going to sound different when driving a loudspeaker that constitutes a complex load. Tube amplifiers fold over and die on the PowerCube test, owing to their impedance-matching transformer. A final PowerCube test is the peak current that the amplifier can source and sink. This is measured with one cycle of a 10 kHz signal into a 0.1-ohm load (a virtual short circuit).

I devoted a good deal of space to the character-

ization of linearity errors in electronics in my introduction to the preamp survey in Issue No. 18. I will not

repeat all that here, but I will summarize a couple of important points. Frequency-independent nonlinearities result in static distortion. Linearity errors which are de-

THE AUDIO CRITIC

pdf 18

Typical Examples of Amplifier Measurements with The PowerCube

Figure 1: The perfect amplifier that never existed.

Figure 3: An amplifier with a poor power supply.

Figure 5: Severe oscillation with a reactive load.

Figure 2: An amplifier with a good power supply.

Figure 4: Very badly designed current limiting.

The PowerCube seeks a target value of 1% THD at 20

data points. It uses 1 kHz sinewave bursts of 20 ms duration. In a separate test it also measures instantaneous peak current (one cycle of 10 kHz into 0.1 Ω).

ISSUE NO. 20 • LATE SUMMER 1993

pdf 19

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