While Waiting for the Perfect Speaker System (Vol. 1, No. 1, Jan/Feb 1977)

While Waiting for the Perfect Speaker System: Duntech DL-15 (comment) ; Acoustat X (comment) ; Phase Linear Andromeda III (comment) ; Infinity QLS (comment) ; Dahlquist DQ-10 with DQ-1W (test report).

Overall, the state-of-the-art speaker scene doesn't seem terribly exciting. We briefly consider a few trendy candidates (after discussing some basic premises in speaker evaluation) and take a closer look at the good old Dahlquist DQ-10 with its impressive new subwoofer, the DQ-1W.

We'll start this with a sweeping generalization and to hell with the risks. In speaker design, the state of the art has advanced very little over the last twenty years.

Twenty years ago the Quad full-range electrostatic appeared on the scene (yes, the year was 1956) and things were never quite the same again. To any ear accustomed to live music, the Quad sounded laughably superior to anything that had preceded it, and no comparable quantum jump has taken place since.

Double-stacked Quads, at their current price of $465 per unit (i.e., $1860 for a double stacked stereo setup), will still give any of the latest super-speakers a hard time in comparative listening tests. No extreme lows, no extreme highs, just exemplary smoothness and detail where most of the music is. For that reason, a lot of highly sophisticated audio people are also using the Quad, with considerable success, as a broadband midrange unit in combination with subwoofers and super-tweeters.

We aren't introducing our first speaker article with these remarks in order to establish a Quad-ueber-alles philosophy for The Audio Critic. That really isn't our thing. (In fact, we hear an ever-so-sight falsification of string sound on the Quad, which we always had our misgivings about, even though it isn't un pleasant.) But we're trying to make two important points.

One is that in speakers, more than in any other component category, the latest and most talked-about is very seldom the best. The other is that any speaker system that aspires to being the "best" must very seriously address the design requirements that have been so carefully dealt with in the Quad. Above all, there must be a high degree of coherence in the output, i.e., low time-delay distortion, so that impulse-type information isn't deformed and phase relation ships are reproduced with sufficient accuracy.

You can actually pick square waves out of the Quad with a measuring microphone over a surprisingly wide range of frequencies.

We believe this is an important criterion, with significant bearing on the audible results (as evidenced also by the recent Hansen Madsen research in Denmark), and that belief will guide us in screening the literally hundreds of high-priced and upper-medium-priced speakers on the market for evaluation in The Audio Critic. We can't test them all, that's for sure.

So we intend to ignore all the big boxes haphazardly stuffed with all sorts of drivers, good and bad, with no other organizing principle in evidence than the desire to achieve a more or less uniform sound pressure level throughout the audio range. Before we get involved in a time-consuming test, we'll need some evidence that both amplitude and phase response have received at least passing attention in the design, that the pros and cons of 6-dB, 12-dB and 18-dB-per-octave crossover slopes have received some sort of intelligent consideration, that diffraction effects haven't been ignored, that the enclosure design has some kind of mathematical basis, and that in general the speaker

has a specific theoretical foundation, no matter how tenuous. That alone will eliminate most candidates and allow us to zero in on reason ably promising developments.

We must admit, though, that for one brief moment about six years ago we thought that Camelot was at hand and that all of the above would soon become irrelevant. The patent is sued to the late Lincoln Walsh for his single cone loudspeaker invention made such brilliant reading, and early prototypes, though faulty, were so exciting in performance, that it seemed someone had finally made an end run around all the unnecessary complications of speaker design and come up with a super-simple approach to perfection. It promised to cut across all price ranges and supersede all other designs, even as the zipper had replaced the buttoned fly in both cheap and expensive pants.

Alas, it was not to be. "Between the idea/ And the reality/. . . Falls the Shadow," as the poet said. The mind-blowing two-dimensional mathematical model of the Walsh speaker didn't translate so easily into three dimensions.

And the small company that obtained the exclusive patent license, Ohm Acoustics, didn't have the R and D megabucks to solve all the problems. Someday, maybe. Meanwhile, the smallest and lowest-priced version of the Walsh speaker, the Ohm G, is by far the best. But- wouldn't you know it-it has been discontinued (at least temporarily) because its relatively modest power-handling capability made it a slow seller. A top-of-the-line 15-inch version, we're told, is a possibility by Consumer Electronics Show time in June.

In the absence of epochal breakthroughs, then, let's have a look at some speaker systems that are at least talking a good design.

Duntech DL-15

We were going to do a detailed test report on this excellent product, but two developments have made that somewhat academic.

The first was the full Richard C. Heyser treatment of the same subject in the August 1976 issue of Audio. Anyone who would re-measure a speaker after it has been measured by the brilliant Dick Heyser has got to be out of his mind. All we're willing to do here is to make some comparative observations that he wasn't allowed to make in a commercial magazine.

The second, and even more relevant, development is that Duntech Labs is mean while out of business. (Another case of an engineering-oriented company seemingly with out a solid business foundation.) You may still be able to locate a pair of these speakers, however, and quite possibly at less than their original list price of $449 per side.

The DL-15 design deserves not to be quickly forgotten, though, because it accomplished something no one else has been able to do. It took three perfectly ordinary drivers (15 woofer, 5 midrange, 13%" tweeter) of the kind available from 'raw speaker' houses, mounted them in a rather sophisticated way (minimizing diffraction) in an enclosure having no special acoustic loading gimmicks, and achieved, if not state-of-the-art performance, something respectably close to it. Plus tremendous efficiency. In a large room that communicates with another fairly large room through an archway and with an upstairs floor through an open stairway, we were never able to measure even momentary amplifier peaks of more than 36 watts, no matter how loud we played the Duntechs. The power handling headroom you get with that kind of efficiency is especially good for piano reproduction, which was the DL-15's strongest suit.

Overall, its sound could be described as "Fulton J junior." A bit on the heavy side (others might say "solid"") but extremely clean, authoritative and musical. The slight impression of heaviness may be due to the apparent Q of 1 of the second-order enclosure (sealed box) configuration, since the response seems to be up about 1/2 dB at the system resonance of 35 Hz according to the Duntech spec sheet. We prefer a Q of 0.707 ("maximally flat"). But on rock-pop material the very slightly looser bass resulting from a Q of 1 may actually be preferred by some listeners who aren't accuracy freaks like us. The slight stridency" in the 3 kHz region that Heyser comments on was evident from time to time, but we didn't find it especially disturbing.

The shortcomings of the DL-15 from the perfectionist point of view became apparent when we A-B-ed it against the Dahlquist DQ-10.

It just didn't possess the super clarity, open ness, imaging and transient detail of the Dahlquist. Switching back to the Duntech for pro longed listening became most unsatisfactory in the course of A-B-ing; it sounded positively dim and muffled by comparison, which of course it isn't when listened to by itself. The fact that the Duntech took with ease some peaks that mildly distressed the Dahlquist didn't change our ultimate preference. Nor did the less extended bass response of the Dahlquist (without subwoofer).

Still, the DL-15 was one hell of a nice speaker. Requiescat in pace.

Acoustat X This large full-range electrostatic system has a great deal of purist appeal, as it is not only crossover-less, with each electrostatic panel reproducing the full audio range, but is also permanently wedded to its own power amplifier, specifically designed to drive these panels optimally. And at $1895 for a complete stereo pair, including amplifiers, it is merely expensive rather than prohibitive.

We haven't tested the Acoustat X under our own roof yet but have taken steps to obtain a pair for review in one of our earliest issues. Meanwhile, we have listened to it as critically as we could, using our own records, at a nearby audio dealer's showroom. Our initial impressions were mostly favorable.

Even to our Dahlquist--conditioned ears, the Acoustat sounded quite open, transparent and accurate in detail. That alone would put it in a small elite group of topflight speaker systems. We detected a bump in the upper bass/lower-midrange response, which could have had a number of causes: room placement, amplifier control over the moving system (we hope that wasn't it!), or the equalization net work used in the speaker to counteract the boundary effect of the rear wall. We'll never know until we test the speaker ourselves.

In any event, this is a rather exciting development for the audio perfectionist, especially since the size of the Acoustat X, while large, is still on this side of tolerability in a reasonably permissive house. Whether it has completely solved the classic design problems that have prevented electrostatics from decisively taking over the high-end market re mains to be seen.

Phase Linear Andromeda III

We haven't heard this new speaker, but on paper it appears to have some interesting things going for it, including what looks like electronic correction for phase and transient effects in the moving system. Also, a dedicated audio freak whose ears we trust has reported to us in glowing terms on the sound of the Andromeda III. 3 None of this would be sufficient cause for even the briefest commentary without some previous listening exposure, if it weren't for a false note in Phase Linear's introductory ad that has set our critical juices flowing.

The ad proudly announces " two twelve inch woofers mounted in a 7th Order Chebechev formula." Quite aside from the misspelling (it should be Chebyshev, at least according to the learned journals we've seen), the capitalization of "order" indicates that they consider the whole thing rather impressive. Just on the face of it, we're not so sure.

The higher the order of a filter (or in this case the alignment order of a vented enclosure), the greater its complexity and the worse its impulse-response behavior. (A sealed box, for example, is a second-order filter.) What's more, a Chebyshev alignment always introduces ripple into the response profile and has poorer impulse response than a Butterworth alignment of the same order, even though it pro vides greater bandwidth for a given output capability (probably the reason for its choice by Phase Linear). A C, alignment is about as extreme from the point of view of degraded impulse response as we've ever heard of. If the Andromeda III has no hangover on bass transients, practice has triumphed most handsomely over theory.

Infinity QLS

We had a chance to hear Infinity's new all-out speaker design (advertised as though they were planning to give up on the unreliable Servo-Statik) side by side with the Acoustat X.

Same showroom, same records, same equipment (except, of course, for the addition of a power amplifier), same occasion as discussed under the Acoustat commentary above. We must repeat that this was a casual audition, not a test. The Acoustat X sounded far superior.

Cleaner, more open, more focused, more accurately detailed, with superior imaging. Considering that the QLS costs $1100 per side (i.e., more than $3000 for a stereo setup with a first rate amplifier, against the $1895 price of the Acoustat), this wasn't a favorable comparison. The dealer claimed, however, that the QLS wasn't set up optimally; they were still experimenting with it.

Supplementing this experience comes the information from one of our staff members that he had the opportunity to do a quickie measurement on the QLS, and the midrange drivers showed a peak of 10 to 15 dB at about 1.5 kHz. He also found that the horizontal dispersion of the "Line Source" tweeters was only fair and their vertical dispersion non-existent. As for the Infinity-Watkins woofer, he found he could easily overdrive it with organ music.

All of this may be nothing more than teething problems in the infancy of a complicated new product. The trouble is, we don't feel very comfortable with the two-voice-coil Watkins woofer even from a purely theoretical point of view. When the original article by William H. Watkins on his new woofer design first came out in the December 1974 Audio, it was privately greeted with hoots of derision by the mathematical academicians in the tight little world of electroacoustics. Their arguments are beyond the scope of this brief discussion (the issue was mainly the exact electrical and mechanical interaction of the two voice coils), but it was rumored that a very distinguished scholar had proposed the article as a possible candidate for the Order of the Purple Bullshit Award.

"If this be error and upon me proved" - if the Infinity QLS should in the end turn out to have obsoleted all existing speaker technologies, as the Infinity ad claims-we'll make a red-faced recantation in Macy's window at high noon.

Meanwhile, we'll stick with our good old Dahlquist, a full report on which follows.

Dahlquist DQ-10 with DQ-1W

Dahlquist, Inc., 27 Hanse Ave., Freeport, NY 11520. Phased Array Model DQ-10, $395. Tested #10766 and #10767. DW-1W Low Bass Module, $275. Tested

#0023 and #0024. All units owned by The Audio Critic.

"The Dahlquist is a great speaker but it has no bass." You've heard that one before, and it was always a pretty good half-truth.

Well, now it has bass. Very accurate bass, too, because the new DQ-1W subwoofer has been designed with the same disregard for plebeian 39 preferences in sound as the DQ-10 itself.

Although the DQ-10 has been widely recognized by audio enthusiasts as a purist's speaker, not too many of them realize just how puristic it is. This is a design that relentlessly, almost desperately, pushes toward the abstract ideal of an output which is linear both in amplitude and in phase. What's more, it does that without permitting itself any prohibitively costly excesses of design, with respect to either components or construction. What the Walsh speaker tried to accomplish with one elegant stroke, the DQ-10 approximates more successfully with brute force. Five drivers per side (not counting, of course, the new sub woofer), an extremely complicated baffle arrangement, an equally complicated crossover network, a rather awkward shape-and it all works. It's almost as if Jon Dahlquist had been standing over his brainchild with a bludgeon in his hand and shouting, "You will be flat and coherent, damn you, if it kills you." We have a feeling that whatever faults the speaker has-and it isn't by any means fault less, but what speaker is?-are due to this straining for perfection within a given price limitation, since that approach leaves no room for easy trade-offs. For example, the use of a relatively inexpensive piezoelectric horn super tweeter is probably responsible for an occasional touch of hardness on the top end, al though this is partly dependent on the associated electronics. Without this somewhat quirky driver, the DQ-10 would still have good highs, but not dead flat out to a zillion hertz, as it does now. It's very easy to give that up, sacrifice some definition and transparency, and end up with a nice, unproblematic, slightly rolled off response that most reviewers would call smooth. But that's not Jon Dahlquist's way.

The DQ-10 is the only speaker we know of that can be proven truly flat in pressure amplitude response. The speaker has a "sweet spot" (much like a golf club or a tennis racket) where our Bruel & Kjaer 4133 measuring micro phone reads an almost amplifier-like straight line response on the screen of our Hewlett Packard 3580A spectrum analyzer. When you move the microphone, the response curve breaks up into the usual peaks and valleys exhibited by multiple-driver systems. But the existence of the sweet spot seems to indicate that the phased-array baffle mounting does make the response coalesce in at least one dimension and that the low-diffraction design has eliminated the ordinarily intractable squiggles from that source. This ridiculously flat response is observable, by the way, from just above 40 Hz on up into the 20-to-40 kHz octave, where we didn't bother to locate the exact roll-off point. (Bats and dogs should worry.) The DQ-1W subwoofer extends the response downwards, of course, but not by as many hertz as you would think. That's not its main virtue.

We'll give you exact numbers in our second issue, where we begin our comparative sub woofer tests (Dahlquist vs. Janis, among others).

Back to the naked DQ-10 for a moment.

We listened to it both without and with the factory-authorized substitution of mylar capacitors for the electrolytics in the cross over network. It makes an audible, though un measurable, difference. The sound is distinctly sweeter, less strained with the mylar mod. (The theory that two capacitors of the same value but different construction can sound different in the same signal path is also shared by Luxman.

They claim to have verified it in amplifiers.) We were also going to perform the factory authorized mirror-imaging mod on our DQ-10's but never got around to it. In any event, it can only improve the accuracy of the stereo image, not the basic texture of the sound.

What about that sound? Even without the subwoofer, it stands up favorably in just about any company. With carefully matched electronics and an impeccable program source, no speaker we know of sounds more open, transparent, clearly detailed-in other words, more accurate-than the DQ-10. Some speakers handle power more gracefully and show less distress when zapped with nasty transients. But these speakers lack the crystalline clarity of the Dahlquist. The DQ-10 can't roar and thunder, but at reasonable living-room levels it sounds more like real music than the roarers and thunderers. Its midrange may still be surpassed by the Quad, by a narrow margin, but overall the Dahlquist lets through more information. It's also a completely unforgiving speaker that will make mediocre power amplifiers. preamps and cartridges sound ridiculous.

Owners of such equipment will invariably hate the Dahlquist. As we said, it isn't the People's Speaker.

What are the negative aspects, then, of the DQ-10 (still without subwoofer)? Other than being a bit light on bass and lacking authority on the hugest climaxes, its only possible fault is the slight hardness or glare noted above, which we'd be inclined to attribute either to the piezoelectric horn or conceivably to the highly complex crossover network. Even this very subtle sonic anomaly varies consider ably with the electronics used, especially the power amplifier. We found that the Quatre DG-250 Gain Cell (an analog multiplier device about which we'll have a lot more to say in our next issue) tamed the DQ-10 more successfully than either the Yamaha B-2 or the GAS Son of Ampzilla. It sounded rounder, sweeter, less "angry" with the Quatre even on difficult material, without losing openness or transient detail. A synergistic combination. (The Quatre can deliver about 150 watts into the load represented by the DQ-10; 200 watts would be even better.) Okay, enter the DQ-1W subwoofer. To avoid any misunderstanding, our opinion of it is based on a totally uncompromising, purist installation. First of all, we got two of them instead of one. That means we didn't use the Dahlquist DQ-MXI passive crossover network (3125), which matrixes the left and right bass signals into a single woofer. Nor did we use the Dahlquist DQ-LP1 electronic crossover ($250) because it wasn't available yet. We used two Quatre DG-250 power amps, one driving the two DQ-10's and the other the two DQ-1W's, and we placed a home-brewed 6-dB-per-octave passive crossover network between our preamp and the two power amps. The crossover frequency was 60 Hz, Dahlquist's recommended optimum. Although there's nothing better than a 6-dB-per-octave passive network for accurate transient reproduction, with a 60-Hz crossover it's down only 24 dB at 1 kHz, and the DQ-1W has enough flux density to be still going strong at that frequency. It should really be rolled off at 18 dB per octave, as it will be in the Dahlquist electronic crossover. To get more roll-off, we blocked off the front of the subwoofers by placing the DQ-10's directly in front of them, so there could be at least no forward radiation of the higher frequencies.

This certainly isn't a standard setup, and our one-on-one judgment of the DQ-1W against other subwoofers will therefore have to wait until the next issue.

But the sound, friends. Ah, the sound.

It changed completely. The DQ-10 was no longer an accurate but light-sounding speaker.

It became an accurate speaker, period. Round and sweet and solid from top to bottom. The

occasional edginess virtually disappeared. It still wasn't full-sounding, since it produced absolutely no bass when there was no bass going in, even outdoing the naked DQ-10 in this respect. But when there was bass going in-organ pedals, bass drum, plucked string bass, Pink Floyd's "heartbeat," you name it--it came out. With impact and without lingering.

Just as in real life.

So this is no subwoofer for bass freaks.

It won't remind you from moment to moment that you've got expensive bass in your system.

The enclosure alignment is second-order Butterworth with a Q of 0.707. That means it's well damped. It won't "woof up" slightly like the second-order Chebyshev alignment with a Q of 1. The system resonant frequency is approximately 38 Hz, which isn't very low but results in decent efficiency in a less than 4-cubic-foot enclosure with a 13" driver. This kind of tuning won't give you 20 Hz flat, if you're one of those who believe they can hear 20 Hz as a pitch. (We can't.) The DQ-1W isn't even a subwoofer strictly speaking. It's simply a very high-quality woofer, the kind the DQ-10 should have come with in the first place. It would have changed the overall shape of the speaker (no great loss!) without adding all that much to the floor space needed by the system.

Suggestion: Why not a vertical phased-array system with a built-in DQ-1W? We'd trade in our present setup for it. And it could probably be made for less than the sum of all these bits and pieces.

One more thing. Some readers may be expecting us to comment on that notorious review in the English magazine Hi-Fi News, writing off the Dahlquist DQ-10 as a mediocre speaker. We really don't know what to make of this aberration by the highly knowledgeable John Crabbe and his staff. Arguments have been going back and forth to the effect that the DQ-10's tested were faulty or damaged, that the review was the last-ditch stand of desperate English snobbism against Yankee encroachment in elitist speakers (but how could anyone feel that way about a nice Swedish-Italian boy like Jon?), and so forth and so on. Frankly, we couldn't care less. Anyone with a reasonably educated ear can hear that the DQ-10 is a top flight speaker, whether or not it's the "best." And anyone who dismisses it as worthless raises doubts about his own credibility, not the speaker's.

-----

[adapted from TAC, Vol.1, No.1 ]

---------

Also see:

The Great Preamp Survey

Various audio and high-fidelity magazines