Sophisticated Speaker Systems, Large and Small: Our Unending Survey (Vol.1, No.6: Spring-Fall 1978)

Part III: In which we conclude that the tweeter is half the battle, redirect our search for a reference speaker as a result, and once again identify some audiophile marvels as fugitives from the laws of nature.

Speakers continue to be our favorite subject. For one thing, they constitute the weakest link and the largest sonic variable in today's audio systems, so we can still look forward to quantum jumps in performance from time to time as new developments reach the market.

Also, our best test program to date is undoubtedly the one we have evolved for speakers. We have a high level of confidence in our evaluations of amplifiers, tone arms or whatever, but we feel we're less likely to be wrong about speakers than about any other class of components. Our combination of frequency-domain, time-domain and listening tests can differentiate quite fine degrees of accuracy or inaccuracy in speaker response and zero in on design trade-off with assurance. We're frankly astonished by the chaotic disagreement among alleged experts about the performance of certain high-priced but obviously poor speakers, whereas on the subject of, say, power amplifiers we can at least appreciate the reasons for controversy even if we don't accept them. (See also our lengthy introductions to Parts I and IT of this survey.)

Our basic test procedure.

We've been through this before, but for the benefit of our new subscribers and to refresh the memories of our old ones, here's a summary of what we do with each speaker that comes in for testing.

We used to start with the listening tests but we no longer do. Too many speakers have been arriving with physical defects and production errors that confuse the issue. Since we want to listen to what the engineers designed, not the goofs of Rosie the solderer or Pablo the shipping clerk, we now listen last, after getting all the laboratory tests down into our notebook.

Our procedure begins with physical inspection. We look at the quality of parts, workman ship, obvious acoustical obstructions, diffractive edges, and above all any sonic ''signatures" that can be elicited by lightly scratching and tapping on each cone and by whacking the enclosure with a padded stick. A lot of speakers begin to reveal their flaws right at this point.

Then come the electronic tests. First, over all frequency response (1/2-inch condenser microphone into spectrum analyzer), followed by nearfield response of each driver (1/2-inch and 1/4-inch microphones, expanded sweeps). On axis and polar response are both analyzed.

Next, impedance curve and determination of woofer Q (unless readily apparent from amplitude response profile). Harmonic distortion is then measured at key frequencies (1/2-inch microphone into distortion analyzer). The all important time-domain tests follow, including dynamic Q (woofer response to step function with increasing drive), tone bursts throughout the audio spectrum, and (perhaps most revealing) widely separated pulses of various durations between about 2 msec and 0.05 msec (0.25 inch microphone). Before the listening tests with actual music, the sound of white noise and pink noise through the speaker is evaluated.

If any easily curable defects are discovered in the course of these tests, such as a loose component, a small air leak or a poor contact, we fix them; we don't, however, attempt to make any speaker sound better than a normal sample of it would. The speakers are then inserted into our "Reference A" system (see the article on reference systems in this issue) and auditioned with a variety of program material. We consider our favorite 30-IPS and 15-IPS tapes, played on a Studer A80 tape deck with Mark Levinson electronics, to be generally the most useful and unvarying points of sonic reference;

a number of outstanding phonograph records, however, are equally revealing. If we're disgusted with the sound of a speaker, the tests don't go on very long, we must confess; the good ones are listened to for weeks on end.

We want to emphasize again, as we once explained at some length, that we don't consider these procedures to be in any way unique or original. We simply believe that they are valid and that as a result we know more about the performance of the speakers we have tested than anyone who hasn't tested them our way.

There may be ways to find out even more, lots more, but not by doing less than what we do.

And certainly not by using unaligned phono cartridges and second-rate electronics as a reference in listening evaluations.

The all-important tweeter.

Here's something we haven't discussed be fore. As a result of certain recent listening experiences, we're just about ready to accept as a psychoacoustic truth the claim that the ear latches on to the leading edge of a waveform, i.e. the "fastest" components of the sound pres sure changes presented to it, and structures its subjective impression of the available sonic in formation accordingly, at least to a very large extent. It seems to be almost impossible to de sign a really bad-sounding speaker system as long as you put a tweeter in it that's very fast and doesn't ring appreciably in the audible range.

The tweeter that taught us that lesson most dramatically is Dick Sequerra's marvelous new Pyramid Model T-1 ribbon tweeter (see review below). But even the KEF T27, fastest of the cheap commercial tweeters, seems to be cap able of turning a sow's ear into a silk purse (viz., Rogers LS3/5A, Tangent RS2, Precedent MZ Mod 3-not particularly sophisticated systems otherwise). And are you old enough to remember the Ionovac? When it worked, which was every other Tuesday, it gave even middling speakers an airy, focused you-are-thereness that was unforgettable. Don't misunderstand us; it's still possible to screw up everything with the midrange and, to a lesser extent, the bass. But the tweeter is half the battle when it comes to achieving some sort of overall subjective realism. That, at least, is the kick we're on at the present moment.

A word about "transmission lines."

As there are two systems reviewed below that utilize the principle of the acoustical labyrinth, somewhat pretentiously and erroneously called the transmission line these days, we want to restate as simply as we can our previously expressed negative views of this design approach. It isn't really wrong; it just wastes space and efficiency, and it doesn't accomplish anything that can't be done much more simply.

Here are the facts of physics. Unless you horn-load a low-frequency driver, which is a very different approach and has a different mathematical model, there are only two kinds of boxes you can put it in: (1) a box with one aperture, namely the driver cutout, and (2) a box with two apertures, the driver cutout and some kind of hole. (Several such holes are merely a modified version of a single hole.) The transmission line is a two-aperture system just like the classic vented box; both have essentially the same mathematical model, with the exception that the transmission line introduces an extra term: a big R for that long resistive labyrinth. Those who believe in vampires, werewolves and the inherent superiority of transmission lines are therefore ascribing some sort of mystical power to that R, as if it were capable of making wonderful things hap pen in addition to resistive damping and a large efficiency loss. We who believe only in the laws of nature, on the other hand, contend that a properly tuned Thiele/Small vented enclosure can have, by definition, exactly the same frequency-domain and time-domain characteristics as a properly tuned transmission line, with the advantage of much smaller size for the same efficiency or much greater efficiency for the same size. In other words, the "perfect" trans mission line can't possibly sound better than the "perfect" vented box, since there exists no third domain.

But wait a minute, that's not quite true.

There's also the money domain, in which the transmission line is far superior. It can be sold for much more money because the consumer can easily see that it's much more complicated.

The logic of numbers extends well beyond science.

On to the reviews....

The Bass Mint Model 10/24

The Bass Mint, 8300 Olentangy River Road, Worthington, OH 43085.

Model 10/24 subwoofer, $475 the pair (single unit, $250). Tested #012 and #013, on loan from manufacturer.

This is, wonder of wonders, a correctly aligned Thiele/Small vented box, the first one we've tested from a commercial (albeit very tiny commercial) source. The model designation stands for a 10" woofer in a vented box tuned to 24 Hz; the alignment is fourth-order Butterworth (maximally flat); the deviations from the corresponding theoretical amplitude response profile are minimal. We measured +2 dB from 20 to 100 Hz, the best small-signal response in any of our woofer tests so far.

Remember, we said small-signal. The 10/24 won't give you that response at 110 dB, like a cathedral organ; its modest 10' driver is capable of only a 1/2-inch cone excursion and the port area is accordingly not made too large. Even so, this woofer gives you deep, deep bass at reasonably loud levels in a 26" by 21" by 19" enclosure at a very decent price-and without any major audible or measurable problems. There's nothing else remotely like it on the market until you get to the Janis kind of money, which is of a totally different category.

Not that the 10/24 is flawless, far from it.

There's a bad buzz at 100 Hz, generally not activated by music but easily elicited with a 5 volt sine-wave drive, which certainly doesn't leave much margin for safety. The manufacturer claims that the buzz has been eliminated in more recent production. There's also much more harmonic distortion at 20, 40 and 80 Hz than we measured in the Janis W-1, for ex ample. Nor is the box as rigidly braced as we'd like; we discern a smidgen of musical coloration of the same quality as the sound of the side panels when thumped, which is a pity since the cone itself is impressively dead. The manufacturer claims that the bracing is also improved in the latest units. Even so, everything considered, this is the best inexpensive subwoofer known to us. The designer obviously did his homework.

Canton Gamma 8S800L

Adcom, 11A Jules Lane, New Brunswick, NJ 08901. Canton Gamma 800L compact speaker system, $598 the pair. Five-year warranty, manufacturer pays return freight. Tested #008249 and #008283, on loan from distributor.

This expensive 11-inch black cube, incorporating a three-way system, is the top-of-the line minispeaker from Canton ( Germany, not China) and is quite typical of the breed. That means it's bumped up in the bass (100 Hz peak, Q = 1.75) and then begins to flatten out; from 1 kHz to 20 kHz it's frighteningly flat (+2 dB); at 20 kHz it's up 2 dB and then drops like a stone; and, of course, it's totally incoherent in the time domain, the three drivers being strictly amplitude matched.

The resulting sound is whompy in the bass and has no focus at all, just as you'd expect.

What you wouldn't expect is a red-hot top end, glary and spitty at the same time. Transient attacks are poorly reproduced. It's a gorgeous little speaker to look at, though; too bad we don't listen with our eyes.

Cizek MG-27

Cizek Audio Systems, Inc., 15 Stevens Street, Andover, MA 01810.Model MG-27 subwoofer, $590 the pair (single unit, $295). Five-year warranty; manufacturer pays all freight. Tested prototypes and early production samples, on loan from manufacturer.

We had high hopes for this subwoofer, which have not been fulfilled so far, although they may conceivably be if the unit is success fully debugged in later production. Our hopes were based on the design concept of the MG-27, which is simple, pure and correct. Two long throw 10" woofers are completely enclosed to yield second-order Butterworth response (maximally flat, Q = 0.707), with the system resonance, and therefore the -3 dB point, at 27 Hz.

This is the perfect alternative to the vented approach exemplified by The Bass Mint Model 10/24 reviewed above; it gives up a few cycles on the bottom by comparison (the box is some what smaller to begin with) but should have slightly better damping characteristics.

Unfortunately, the prototypes as well as the early production samples we looked at were full of buzzes, air leaks, impedance ripples, and all sorts of glitches in the response profile, making their potential sonic capability almost impossible to evaluate. There was really no frequency below 100 Hz where they didn't buzz at least a little bit. Some of this is probably curable; however, we also suspect circumferential resonant modes caused by the mass-loading of the driver cones at the apex, which is a basic design problem.

Another peculiarity of the MG-27 is that, when a supposedly matching Cizek Model #2 speaker system is '"'correctly'' connected to its built-in passive crossover, the two systems are amplitude matched but out of phase. When you put them back in phase by "incorrectly" reversing the leads (red to black, black to red), there's a 10 dB suckout but more transparent sound. We don't believe in phase reversal as an amplitude matching technique.

We want to reserve final judgment on this basically honest and intelligently conceived product until Cizek gets the whole act together.

Fried Model B/2

Fried Products Co., 7616 City Line Avenue, Philadelphia, PA 19151. Model B/2 Mini Monitor, $500 the pair. "In definite" warranty, at discretion of manufacturer. Tested #XB005 and #XB006, on loan from manufacturer.

This is a Rogers-size minispeaker, with a mild cultist aura that emanates chiefly from the manufacturer, and various little mods and retrofitting recommendations announced at frequent intervals to keep the faithful hopping.

It can be used either separately or as a "'satellite" of the Fried Model T subwoofer (see re view below). Actually, it's a good little speaker, comparable to other good little speakers ( Rogers LS3/5A, Tangent RS2, Symdex Sigma), all' of which opt for different design trade-offs and performance compromises.

The B/2 gives up some speed and, especially, dispersion in the tweeter (see also our tweeter discussion above, before the reviews) by using a relatively large one to gain power handling and dynamic range. The 5" midrange/woofer cone also handles power surprisingly well. The over all sound of the speaker is quite uncolored, free from stress and well-defined, lacking only the ultimate detail and airiness possible with a different approach to tweeter selection. That, how ever, is an important reservation.

The axial response of the system is within +3 dB from 70 Hz to 22 kHz, except for a peak of 4 dB at about 1.1 kHz, where we also ob served some severe ringing on tone bursts; the tweeter is flat only to 15 kHz at 20° off axis and keeps rolling off as the angle increases; further more the tweeter produces an extra cycle on tone bursts throughout its range and looks a bit slow on the first cycle. It all figures. Pulse replication is basically good, though, to 0.1 msec and even a little beyond. As for the Q of the midrange/woofer in its box, it's very close to the ideal 0.707 and stays there even with in creasing drive.

All in all, as you can see, we have no major complaints about the B/2 but we can't get terribly excited about it, either. It doesn't seem to have any crippling defects but at the same time lacks the breath of life possessed by other two-way dynamic speakers designed with different priorities, such as the Tangent RS2 and the DCM Time Window.

Fried Model T

Fried Products Co., 7616 City Line Avenue, Philadelphia, PA 19151. Model T two-channel transmission line subwoofer, $1400. "Indefinite" warranty, at discretion of manufacturer. Tested #T10113, on loan from manufacturer.

You can look at this double transmission line subwoofer two ways. You could say that it contains two very decent 10"* woofers in properly damped enclosures, one for each channel of your stereo system (less than 4 feet apart, to be sure), with reasonably flat frequency response down to the -3 dB corner of 35 Hz. Or you could say that it's the most insane cult item in all audiodom, since a pair of Cizek 10" book shelf systems will give you just about the same response profile and comparable damping characteristics for $396 instead of $1400, with tweeters thrown in; and for $475 a pair of Bass Mint 10/24's will go down almost an extra octave below the Model T.

Please go back to our remarks about transmission lines in the introduction to this article. This is a classic case; the Model T occupies approximately 12 cubic feet of space, weighs 175 pounds, costs more than any other pair of woofers we can remember offhand- and it's nothing more than a good, clean 35 Hz box. Please don't ever say that we knocked the performance; the Model T sounds good.

Just like other good, clean 35-Hz boxes.

Well, as a matter of fact, we found some thing that wasn't so clean: when pulsed, the unit produced a spurious second blip 25 msec behind the first pulse, through the transmission line.

This was just audible as a slight thickening of the sonic texture; however, the manufac turer informs us that a new mod eliminates this condition (in fact, they offered to fix it in our sample, but our tests were over by then), so we don't want to make a federal case of it.

A pair of Model B/2's connected to the slow-slope passive crossover available on the back panel of the Model T add up to the Fried Model H/2 System. How does it sound? Not quite as focused in detail at a pair of B/2's alone, although the bass is extended by an octave. We're giving it the benefit of the doubt, though, in view of the mod that eliminates that 25 msec delay.

Janis W-1 (follow-up)

Janis Audio Associates, Inc., 2889 Roebling Avenue, Bronx, NY 10461. Model W-1 Subwoofer System, 81350 the pair (single unit, $675). Tested #141588 and #141589. Interphase 1 Electronic Crossover/Bass Amplifier, $990 the pair (single unit, $495). Tested #10122 and #10123. All samples on loan from manufacturer.

Here's a rather special case requiring an upward revision of a previous evaluation. We now consider the Janis W-1 to be the best sub woofer on the market, regardless of price. In our original test (see Vol. 1, No. 2, pp. 32-34), we found the W-1 to be almost dead flat from 100 Hz on down to 30 Hz (-3 dB at 26 Hz) and incredibly low in THD, but it seemed to make everything sound thick, opaque and unfocused, even though the electronic crossover was correctly set for a perfect amplitude match to the rest of the system at 100 Hz. We suspected some out-of-band peaks, particularly one at 460 Hz (i.e, more than two octaves above the crossover), to be the culprit, especially since such peaks are a necessary concomitant to the unique slot loading used by Janis.

Well, what has changed? It would be an easy out for us to report merely that a minor internal modification has changed that 14 dB peak at 460 Hz (without crossover) to an 8 dB peak at 420 Hz, and that through the 18-dB per-octave crossover the whole thing is now be low some kind of audible threshold that was exceeded in the original version. That may be part of the reason but it isn't the whole story.

The fact is that the Janis W-1 energizes the whole room in the bottom octave of the audio range like no other woofer, and our reference turntable at the time (Luxman PD-121) was much too active acoustically in that kind of sound field. Unfortunately, this happened when we hadn't quite phased in our master tape listening tests yet. Another difference is that the Janis has now become a bass system, instead of just a subwoofer, through the avail ability of the matching Interphase 1 bass amplifier, which has carefully tailored complementary electrical characteristics plus a built in electronic crossover with straight-wire by pass switching capability (woofer in vs. main system alone). The latter feature convinced us that the electronic stages of the crossover are inaudible.

We haven't formally bench-tested the Interphase 1 yet but can report that it works beautifully with the W-1. As for the subwoofer itself, a pair inserted into our reference system is currently giving us the best bass of our life time, rock solid, wide open right down to the bottom limits of the program material, and with that realistically breathy quality that only the accurate reproduction of the lowest frequencies can bring out.

Mind you, we don't consider the Janis to be the theoretically perfect woofer. It's basically a high-efficiency narrow-band resonator (its mathematical model actually has two apertures in series) that barely gets away with cheating Mother Nature by stonewalling its very restricted linear range with steep cross over slopes. (We're told that a 36-dB-per octave Janis crossover is coming soon, indicating that John Marovskis himself sees the problem that way.) Nor can the W-1 produce 125 dB at 20 Hz, which is what you get in real life under extreme conditions. But, then, why should the woofer be more perfect than the rest of the system? The Janis may be a some what questionable electroacoustic sleight of hand, but at least it works-right here and right now.

Magneplanar Tympani I-D

Magnepan, Inc., 1645 Ninth Street, White Bear Lake, MN 55110. Magneplanar Tympani I-D speaker system, $1395 the pair. Tested #044646, on loan from dealer.

We haven't been able to figure out so far why this speaker has a fanatical cult following.

That usually happens only to exquisitely good or perversely bad products, and the "Maggie" is neither. It's merely a valiant but not quite successful attempt to fool Mother Nature.

As you probably know, the Tympani I-D consists of a pair of triple screens or room dividers, the entire surface of which is active, front and back. It's a true dipole speaker, with all the advantages and disadvantages of the breed. It also tries to be a force-over-area transducer but doesn't quite make it. That grid of wires acting as a distributed voice coil doesn't have total control of the diaphragm in the same sense as the electrostatic field controls every square millimeter of the membrane in an electrostatic system. A number of problems arise as a result.

Typical dipole response is characterized by a 6-dB-per-octave falloff below a certain frequency, as an inevitable consequence of back-to-front phase cancellation. The Magneplanar design tries to cheat this law of nature by amplitude matching the bass panels to the midrange. The resulting power response into the room, copied by our measuring micro phone edgewise to read the sum of both dipole lobes, is indeed flat down to 40 Hz, with the half-power (-3 dB) point at 36 Hz. The monopole characteristic, on the other hand, is bumped up approximately +6 dB at 40 Hz, with heavy consequences in the time domain.

The response to a step function indicates a dynamic Q in excess of 2, which isn't exactly tight bass, and that figure appears to rise with increasing drive. You can't eat your damping and have it too.

The midrange of the Tympani I-D is generally quite smooth; the highs are rougher, with a vicious peak at 14 kHz, where we also observed some severe ringing. The tone burst tests showed at least two extra cycles produced by the speaker at all frequencies, and more where there was actual ringing (e.g., at 14 kHz). This is very poor performance and indicates serious energy storage problems in those large panels. There's obviously no force-over area control. The pulse tests turned out to be the most interesting, as they revealed the en tire character of the speaker. The pulse shapes looked excellent at all widths down to 0.15 msec, but each pulse was followed by a long trail of overhang ripples. In other words, the fast part of the signal was accurately reproduced, but spurious energy came out of the speaker for a much longer time.

And that's exactly what the Maggie sounds like. Its sonic signature is 'snap-blur.' Clean attack, followed by a wash of vagueness. Those who say it has excellent transient response are right, in a sense; those who feel it's unclear are also right; those who insist it's one of the world's great speakers don't know what they're talking about. For example, a 30-IPS master tape of a solo acoustic guitar played through the Magneplanar had a peculiarly smeared, hollow sound until we switched to a pair of Tangent RS2's.

Instantly, the guitar became a focused presence in a three-dimensional space. It was almost embarrassing, with the 3-to-1 price ratio of the two speakers and not even a decent measure of doubt as to which was more accurate.

Despite all this, we don't find the sound of the Magneplanar Tympani I-D unmusical; it's quite pleasant and listenable. But a reference speaker it isn't and will never be.

Precedent MZ Mod 3

Precedent Audio Products, Inc., 306 East Oliver Street, Baltimore, MD 21202. MZ Modular 3 speaker system,. $1333 the pair. Three-year warranty. Tested samples on loan from manufacturer.

In a world of good, bad and mediocre speakers, this would have to be classified as a good speaker, but that doesn't mean we admire the design or are wild about the sound.

The best part of the MZ Mod 3 is the KEF T27 tweeter, which goes out smoothly to 35 kHz (yes, thirty-five) and hardly rings at all at any frequency. If you've read our comments about the importance of tweeters in the introduction to these reviews, you know what that means. There can be no doubt that the MZ Mod 3 sounds open, airy and "present." Since all three drivers (all KEF, by the way) are en closed in separate modules, we can then move down to the next best part, the woofer. This is a transmission line and, to refer you back again to the introduction where we discuss trans mission lines in more detail, that means it comes out in exactly, but exactly, the same place where a smaller and cheaper Thiele/ Small vented box would have, using the same driver. But at least it's decently executed, so the response is flat and smooth down to about 40 Hz, below which it drops rapidly; the damping appears to be correct and tone bursts elicit no misbehavior. So right away you can surmise that the MZ Mod 3 has a solid, well-con trolled, clearly defined bass, and you're right.

But that's an expensive 40-Hz box, fella.

Now comes the not-so-good part, the mid range module. This is also sold separately, in conjunction with the tweeter, as a complete small system at half the price. It goes down surprisingly low (as a separate system) and is also a transmission line, but a lot messier than the bass module. On tone bursts, it gives you five cycles for the price of four anywhere above 400 Hz and also dumps all kinds of additional garbage between | kHz and 5 kHz, including ringing, cancellations, envelope variations, you name it. The crossover network that puts all this together is even messier, synthesizing anomalies that would take a whole treatise to analyze, and it drives the tweeter out of phase with the midrange and woofer, so that the sys tem produces only a kind of *"'facsimile' pulse but no genuinely coherent wave front. The KEF tweeter is able to define the beginning and end of a pulse, and the midrange and woofer fill them in after a fashion, but true coherence it ain't.

The faulty midrange cramps the style of the tweeter and the woofer, so that the total sound is a bit glary and hollow, with a sense of strain. What could have been a really fine, though needlessly eccentric, speaker ends up as, eh, pretty good. And not cheap.

Pyramid Model T-1

Pyramid Loudspeaker Corporation, 131-15 Fowler Avenue, Flushing, NY 11355. Model T-1 Ribbon Tweeter, $990 the pair. Three-year warranty. Tested #0163 and #0164, owned by The Audio Critic.

This is without doubt the most exciting product reviewed in this issue. It has changed our audio life. What more can we say? We're not even sure whether Dick Sequerra fully realizes how good his new ribbon tweeter is; at one time he was equally messianic on the subject of the Metronome speaker.

A limp ribbon in a strong magnetic field is the theoretically perfect force-over-area transducer; how we wish somebody made one as tall as the Beveridge speaker. (Many years ago, we're told, a bunch of audio-freak scientists at the University of Chicago stretched a large sheet of Reynolds Wrap in the gap of the cyclotron and fed some music into it. They've never been satisfied by any speaker since. When we told this story to Mark Levinson, he seemed very interested and started calling his production people.) The trouble is that the right mag net is terribly expensive and so is a really good transformer, the latter being absolutely necessary for the impedance match between the virtually zero-impedance ribbon and the power amplifier. The Decca ribbon tweeter, for ex ample, which costs less than the Pyramid, has a rather skimpy transformer that rings quite badly, even though the transducer itself is very accurate. (We found that out in an impromptu test of a borrowed unit.) We have a pretty good idea what the cost of the parts is in the T-1, and, believe it or not, it isn't a high-profit item even at its exorbitant price.

So here's what Dick Sequerra did. He put a large ribbon (larger than the Decca or the old Kelly) into an extremely powerful magnetic gap to achieve the highest possible efficiency.

He made a matching transformer for it that goes down to 100 Hz, even though the tweeter is used only above 3 kHz. He designed a 5 position filter /attenuator for level matching as well as crossover. And he put the whole thing together in a slightly pyramidal (aha) black metal case. The result is the best tweeter in the world, at least the world we're familiar with.

First of all, the frequency response is al most as smooth as that of an amplifier. None of the usual jagged speaker profile. There's a slight downward slope, absolutely straight, which may be due to mass or is possibly a characteristic of the filter/attenuator. (The latter varies the response profile slightly at different settings, a feature we didn't like at all; a more sophisticated network may be necessary.) This gentle, linear slope continues al most indefinitely into the ultrasonic region.

In other words, the tweeter isn't absolutely flat but is extremely wideband, fast and smooth. Its rise time is hard to measure be cause it approaches that of the measuring microphone itself. Some early samples we looked at showed quite a bit of ringing on tone bursts at a few discrete frequencies, but the units we finally put into our reference system have greatly improved mode suppression and don't ring appreciably. The white noise and pink-noise sound of the tweeter is considerably less grainy than that of conventional cone and dome units. Best of all, the T-1 can handle almost unlimited power; it will self-destruct before it overloads acoustically.

Needless to say, we aren't calling this the world's best tweeter because of its performance on the lab bench. It's what it did when connected to various speakers that sold us. The first speaker we tried it with was the Tangent RS2 and immediately we heard a clarity, open ness, definition and headroom that in some ways made the combination already preferable to the Beveridge. (Not in the midrange, of course.) Further experiments with other dynamic speakers indicated that the tweeter could make almost any half-decent system into a virtual SOTA contender, at least in some respects. That's how we arrived at our conclusion about the decisive role of tweeters as discussed in the introduction to these reviews (see above). When we finally mated the T-1 to a suitable electrostatic midrange, we had a Beveridge beater for sure (see the article on reference systems elsewhere in this issue).

The last little fillip was added when we connected the T-1 to the latest modification of the Futterman amplifier. We can honestly say we've never heard a cleaner, smoother, more detailed top end than that, ever. Now we can't stand listening to anything else.

Maybe that much abused word 'breakthrough' is for once appropriate. At last we have a reference standard, meaning something so accurate and clean that it instantly shows up anything plugged into it that's less accurate and clean. It makes us sad to ponder, though, that various influential audio people who don't have their act together, who ignore the whole question of phono cartridge alignment and use moving-magnet cartridges, acoustically active turntables, unstable amplifiers, etc., will try the Pyramid T-1 and find it to be just another tweeter. On the other hand, Dick Sequerra can't make all that many of them, anyway, so it's probably just as well that not everyone will share our enthusiasm.

Symdex 'Sigma' Symdex Corporation, PO Box 927, Framingham, MA 01701. 'Sigma' loudspeaker, $598 the pair. Tested #091507 and #091508 (also auditioned #101601 and #101602), on loan from manufacturer.

The officially avowed intention of this small new firm with their first product, the Sigma two-way speaker system, is to exceed in accuracy all previous dynamic loudspeakers from 60 Hz to the limits of audibility, with an optional woofer to be brought out later for ex tending the range downward. They claim to have looked into and optimized everything: "time delay distortion, frequency response, dif fraction, system Q, and early reflections," ac cording to their literature. If that's true, the Sigma ought to clobber all the other expensive small speakers, including the Rogers LS3/5A, Tangent RS2, Fried Model B/2-anything with a small woofer and tweeter. And in some ways it does, but there are trade-offs, as usual.

With the measuring microphone at the "sweet spot," the Symdex speaker has impressively flat frequency response, from the -3 dB corner at 60 Hz right on up to the ultrasonic region, and possibly the best pulse response we've ever measured, not even excepting the Beveridge. When the mike is moved, however, the pulse response deteriorates; the cone of coherence is quite small, so Harold Beveridge can relax. Exploring the nearfield at points other than the sweet spot also reveals a slight but unmistakable saddle in the frequency response, with the dip at 1 kHz. Tone bursts are excellent throughout. Overall, this is still quite brilliant test bench performance.

There were two little things we found, how ever, that we didn't like. One was that the system Q, which is in the desirable 0.7 to 0.9 ball park on small-signal analysis, migrates to approximately 1.3 at high drive levels. The voice coil obviously comes out of the gap. The other peculiarity was that the small Audax soft-dome tweeter (one of the really good ones in the business, dead flat to 20 kHz and good to 33 kHz, rivaling the KEF T27) appeared to be receiving full power down to 800 Hz, al though the nominal crossover frequency of the first-order dividing network is several octaves higher than that. This is bound to overload the tweeter from time to time and dump side bands all over the spectrum.

Both of these problems are made more serious by the fact that the speaker is extremely inefficient, so that it's quite likely to be driven hard enough to activate both distortion mechanisms.

In our listening tests the Symdex appeared to have the least coloration (most neutral sound) among our favorite dynamic speakers, as well as the best balance and most distinctly focused image. We didn't, however, like its dynamic behavior. It didn't seem to "breathe" with the ebb and flow of the music and appeared to have a slightly strangled quality on dynamically varied program material. This was alleviated to some extent by crossing it over to the Janis woofer at 100 Hz, but not entirely.

The two faults we had found in the lab may have been the reason.

Overall, we don't quite know where to rank the Symdex Sigma. In some ways it's better than either the DCM Time Window or the Tangent RS2, our two favorite time coherent dynamic speakers so far; in some ways it isn't. The Time Window, especially, is more satisfying musically with its better headroom, even though it's obviously more colored in the purely objective sense. Our feeling is that the Symdex is the product of a single-minded, one-dimensional perfectionism, in a restricted design format that yields perhaps more readily to the seasoned compromiser. Still, it's an auspicious start for what looks to us like a very serious young company.

Thiel Model 03 (interim report)

Thiel Audio Products Company, 4158 Georgetown Road, Lexington, KY 40505. Model 03 floor-standing coherent-source loudspeaker, $775 the pair. Tested #0009 and #0010, on loan from manufacturer.

This was planned to be a full-fledged re view but has turned into an interim report be cause the early samples that were rushed to us are no longer representative of the product. The all-important midrange has apparently been totally revised. We're waiting for new samples.

Meanwhile we merely wish to point out that this very handsome unit is directly competitive with the DCM Time Window in size and audiophile appeal; it will have to out perform the latter in order to justify the $115 difference in price, though. In one respect it definitely outperforms the Time Window; the electronically equalized sixth-order Butter worth response of the vented bass enclosure is dead flat down to 28 Hz and -3 dB at 25 Hz.

That's the small-signal response, of course; from 50 Hz on down to 20 Hz you can't drive the woofer very hard without creating a great rushing noise through the vent. This part of our measurements is unlikely to change with the new samples.

Also like the Time Window, the Model 03 is carefully aligned for time coherence; the pulse response looked excellent. But we have no idea what the final production units will sound like.

Watson Laboratories Model 10-H

Watson Laboratories, 2711 Rena Road, Mississauga, Ont. Canada L4T 3K1. Model 10-H speaker system, $1950 the pair. Tested #417L and #418R, on loan from manufacturer.

Mike Wright, the original founder of Dayton Wright and inventor of the XG-8 electrostatic, attracts a cult following no matter what he does and where he goes; his new line of dynamic speakers under his new brand name (he sold Dayton Wright to Leigh Systems) has consequently been spoken of in hushed tones in some circles, but we ended up being very disappointed with the top-of-the-line Model 10-H.

We don't feel any desire to do a number on it driver by driver (there are two in the woofer and seven in the top section, per side!); luckily we have a perfect out because the units we tested had been manufactured in March or April, 1978, and just barely missed getting into our last issue, so there's a strong possibility that current production models are better. Mike Wright isn't the kind of engineer who leaves bad enough alone.

Basically the problem we found was that this is a strictly frequency-domain oriented design, with no attempt at coherent geometry, no recognition of the dangers of energy storage, no control of system Q, no attention to the time domain at all. The speaker did very poorly on every one of our tests (as listed in the introduction to these reviews), with the exception of frequency response, which was decently flat from 28 Hz to beyond 20 kHz-but only at the "sweet spot." With the multitude of drivers pointing every which way (a design approach we could never relate to), it was difficult to get even that result. The gas-filled woofer en closure (a Wright hallmark) had its own special, and especially horrendous, resonances; nothing really worked perfectly on our samples.

The resulting sound was blurred, diffuse and very indistinct, creating the impression of a totally noncoherent field. The poor definition was aggravated by a wiry quality on top; a tub by, poorly controlled quality in the bass; and a nasal, hollow, boxy quality overall. We sure hate to end our reviews on this note, but we tested no speakers beginning with X, Y or Z.

Recommendations

As our reference system gets better and better, we're becoming less and less tolerant of the shortcomings of even the best small speakers (Rogers, Tangent, Fried, Symdex, etc.). We're therefore dropping that category from our Recommendations, even though the speakers sound just as good as they ever did.

Read the reviews and suit yourself.

Best speaker system: Reference A of The Audio Critic (see article on reference systems).

Best speaker system from a single manufacturer: Beveridge System 2SW-1.

Best speaker system per dollar: DCM Time Window.

Best tweeter: Pyramid Model T-1.

Best subwoofer: Janis Model W-1 with Interphase 1.

Best subwoofer per dollar: The Bass Mint Model 10/24.

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Speaker Summaries and Updates

These reviews appeared in Volume I, Numbers 1, 2, 4 and 5.

Acoustat X Acoustat Corporation, 4020 North 29th Avenue, Hollywood, FL 33020. Acoustat X full-range direct-drive electrostatic speaker system, 82200 the pair (with built-in power amplifiers).

A crossover-less full-range electrostatic speaker driven directly off the plates of its matching amplifier's output tubes-what could be a purer concept? Unfortunately, the design is badly flawed, with obvious standing waves in the panels, bad ringing at quite a number of frequencies, and no coherence on pulse reproduction. There are also bad lobes in the polar response and horrible overload in the 35 Hz region.

As a result, the speaker is incapable of sounding as smooth, effortless and focused as a sophisticated electrostatic is expected to. The newer Acoustat Monitor ($3000 the pair) is an expand ed version of the same basic system.

Beveridge System 2SW-1

Harold Beveridge Inc., 505 East Montecito Street, PO Box 40256, Santa Barbara, CA 93103. Beveridge Cylindrical Sound System, Model 2SW-1, 87000 the pair (including plug-in direct-drive tube amplifiers, HD subwoofers, solid-state bass amplifiers, electronic crossovers and CM-1 control module).

This is the latest version of a marvelous electrostatic; what we tested (System 2SW, $6000 at the time) was identical from 100 Hz up, so there can be no great surprises. The 2SW-1 modification includes slightly revised woofers (Q = 0.707 is claimed), with matching bass amplifiers, plus a new electronic crossover. Our judgment is that it can only sound better, certainly not worse, than the 2SW, which was the best speaker system we had tested before assembling our own Reference A.

We still consider the coherent cylindrical sound field of the Beveridge to be superior to the radiation geometry obtainable with Reference A, and we don't know of a more transparent midrange than that of the Beveridge, either. Compared to the Pyramid Model T-1 tweeter, however, the Beveridge has somewhat rolled-off highs; the bottommost bottom just isn't like that of the Janis; and the dynamic headroom of the system is quite inadequate by ultimate standards. Still, for many people, this will remain the ultimate system because of the way it "illuminates" the room with sound.

Braun 'Output C' and L200

Adcom, 11A4 Jules Lane, New Brunswick, NJ 08901. Braun 'Output C' miniature speaker system, $230 the pair. Braun 1,200 small bookshelf speaker system, $270 the pair.

Just about the smallest high-fidelity speaker in the world (Output C) and its very similar "big" brother (about twice as large but still smaller than the Rogers)-are you interested? They're a bit bumped up at the system resonance to fake the bass, and their tweeters ring quite a bit, but the sound is amazingly listenable, maybe a little on the zippy side. Not for the purist, though.

Canton HC 100 and LE 400 Adcom, 11A4 Jules Lane, New Brunswick, NJ 08901. Canton HC 100 miniature speaker system, $190 the pair. Canton LE 400 bookshelf speaker system, $350 the pair when tested (no longer listed under this model designation).

Also from German, like the two Brauns above, and com parable. The HC 100 is teeny-weeny like the smaller Braun and similarly bumped up on the low end; its tweeter is cleaner, though. The LE 400 is about half a cubic foot in volume and has better bass, as well as an astonishingly flat, fast tweeter that almost fools you with its openness and presence, until the lower treble ringing gets to you and you realize that the system is quite fatiguing and over-bright and "electronic". Neither Canton has even nodding acquaintance with time alignment, so the inner detail is quite unfocused as a result.

Cizek Model #1 and Model #2 Cizek Audio Systems, Inc., 15 Stevens Street, Andover, MA 01810.

Model #1 and Model #2 acoustic-suspension loudspeakers, $396 and 8268 the pair, respectively.

These are virtually identical two-way systems, #1 with a 10" and #2 with an 8" woofer. In contrast to the Rogers-type minimonitors with their tiny midrange/bass drivers crossed over at a high frequency, the Cizeks give you solid, correctly damped bass down to 38 Hz and a 1.5 kHz crossover that puts much more of a power demand on the tweeter. The resulting design trade-offs end up as somewhat zingy and edgy sound, not nearly as refined as that of the minimonitors. On the other hand, it's still a very decent sound for this kind of money.

Dahlquist DQ-10, DQ-1W, DQ-LP1

Dahlquist, Inc., 27 Hanse Avenue, Freeport, NY 11520. Phased Array Model DQ-10, 3850 the pair. DQ-1W Low Bass Module, $550 the pair (single unit, 8275). DQ-LPI1 Variable Low-Pass Filter, $250.

The DQ-10 was the first truly sophisticated dynamic speaker system of the mid-1970's; it still stands up quite well but has since been bested in clarity and listenability by a number of cheaper speakers. Its ''clubfoot" is the Motorola piezoelectric horn tweeter, which is totally incapable of passing recognizable pulse-type waveforms. The DQ-1W is a well designed sealed-box woofer; however, its -3 dB point is at 42 Hz, and that's not good enough to give you the bottommost notes of the organ and such. The DQ-LP1 is a combination active low-pass and passive high-pass filter for biamping; it can't possibly add distortion on top and does its job very nicely on the bottom, with variable crossover frequencies. Highly recommended for the money.

Dayton Wright XG-8 Mk 3 Series 3

Dayton Wright Associates Limited, 350 Weber Street North, Waterloo, Ont., Canada N2J 4E3. XG-8 Mk 3 Series 3 full-range electrostatic loudspeaker, $3295 the pair.

One of the biggest cult items in the history of high-end audio, this electrostatic is a real turkey in our book. Peaky,

with severe ringing at numerous frequencies, it sounds honky and unclear in the midrange, hard and zingy on top. It's possible that much earlier versions sounded better; stay away from this model, in any event.

DCM Time Window

DCM Corporation, 2275 South State Road, Ann Arbor, MI 48104.

Time Window floor-standing loudspeaker, $660 the pair.

Since we last wrote about the Time Window, minor modifications have again taken place. We rechecked the latest units. The capacitors in the crossover network are now Mylar;

the bass has been flattened out slightly and extended very slightly (the -3 dB corner is now at 48 Hz); the tweeter peak has been reduced but it's still there (this time at 13 kHz, still ringing); the tweeter response now goes out flat to 15 kHz and is down "only" 10 dB at 20 kHz. The excellent pulse response has been retained but the tweeter is still out of phase. The net result of these small improvements is to confirm our ranking of the Time Window as the relatively best choice among all the highly imperfect speakers in this price range. Yes, it has a slightly hollow quality in the upper bass and lower midrange; it doesn't even give a tremendous sense of immediacy; but its openness, balance, excellent dispersion and remarkable headroom (for this type of speaker) give it the breath of life when it plays music.

Fundamental Research

Fundamental Research, 1304 Success Street, Pittsburgh, PA 15212.

'The Low Frequencies' subwoofer, $900 the pair (single unit, $450).

When we tested the original Fundamental Research sub woofer, we couldn't find much wrong with it except that it was overdamped, so that it didn't take full advantage of its fairly large dimensions to go down flat as low as possible. The revised version, which we have more recently tested, is still overdamped (Q = 0.58, 0 dB at 60 Hz, -3 dB at 40 Hz, -9 dB at 20 Hz); we don't believe that the slight time-response advantage with such a very low Q is audible, whereas the loss of amplitude response is. What's more, the subwoofer now has two 10" drivers in parallel, instead of the previous single 12", with the result that the impedance is down to 3 ohms across a fairly wide band of frequencies. We don't think that's quite right; it can blow out amplifiers that way. Apart from that trifle, we still like every thing; the Q is retained at all available drive levels, tone bursts look good, the sound is very clean and tight-but the bottom of the bottom end isn't there.

Hartley 24" Subwoofer Hartley Products Corporation, 620 Island Road, Ramsey, NJ 07446.

24-inch Woofer-Driver, $375 each (without enclosure).

This is an irrational design: a 24" woofer with a puny 112" voice coil pushing its 21.5" cone and with a free-air Q of ap proximately 0.7, so that it can't possibly be enclosed in a sealed enclosure of less than 50 cubic feet or so without making it woof up and whomp and ring. In a mere 18 cubic feet, the Q is 2 and the bass hump +6 dB at 48 Hz. The cone has an aluminum tube sticking out from the middle, purportedly a heat sink for the voice coil, but actually a peaky "supertweeter" that goes out to 29 kHz! The fact that the Hartley can grab a lot of air in the midbass and make it move is its only redeeming feature, but who specified these ridiculous parameters and what were his reasons?

Infinity QLS

Infinity Systems, Inc., 7930 Deering Avenue, Canoga Park, CA 91304.

Quantum Line Source speaker system, $2500 the pair.

With 17 drivers per side and totally bollixed-up radiation geometry (the "line source' appellation is a joke), there just can't be any real focus, inner detail and stable imaging-and there isn't. The 'EMIT' tweeters, by themselves, are quite excellent but very inefficient; the midrange domes are peaky; the 5" midbass driver rings like a telephone; and the 12" Watkins woofer can't take the biggest bass wallops. The overall sonic results are on the decent side of mediocre, that's all; this is no reference speaker. And that makes us wonder about the new Infinity QRS at $6500-do these people really listen?

Innotech D24

Innotech, 42 Tiffany Place, Brooklyn, NY 11231.

Model D24 floor standing speaker system, $854 the pair.

The tweeter is good; the midrange dome rings severely throughout its range; the woofer is a somewhat bumpy 50-Hz box. Highly colored sound with a distinctly "canned" quality.

Janis W-2 Janis Audio Associates, Inc., 2889 Roebling Avenue, Bronx, NY 10461. Model W-2 Subwoofer System, 3900 the pair (single unit, $450).

The W-2 is virtually identical to the W-1 (see Janis follow up review above) with the exception of the last few Hz on the bottom, where the W-1 stays flat and the W-2 starts rolling off.

Thus, our favorably revised evaluation of the Janis bass system is likely to be equally applicable here, although we haven't retested the W-2.

Koss Model One/A

Koss Corporation, 4129 North Port Washington Avenue, Milwaukee, WI 53212. Model One/A full-range electrostatic speaker, $3000 the pair.

So far, nobody but Koss seems to be able to make electrostatic panels that can handle large amounts of power in ordinary air. (Dayton Wright uses a sealed, gas-filled environment.) The One/A is a very respectable speaker system;

offhand we can think of only three others that will give you even greater clarity, better detail, and a cleaner impression overall, all at a higher cost: our own Reference A (which also uses Koss panels in the midrange), the Mark Levinson HQD System, and the Beveridge; but the latter can't play nearly as loud. The Koss does have a "'clubfoot" though; there's a rather severe and in tractable high-Q resonance at 50 Hz, which tends to dump colorations into the lower midrange. With a little cleaning up this speaker could become a very good buy even at its increased price.

Ohm F

Ohm Acoustics Corp., 241 Taaffe Place, Brooklyn, NY 11205. Ohm F 'coherent sound' speaker system, $1400 the pair.

The single-driver Walsh principle really works, up to a point; the Ohm F reproduces pulses of all widths with remarkable coherence. The large metal cone (deployed with its convex side out and apex up) creates tremendous energy storage problems, however; the ringing we measured at numerous frequencies throughout the speaker's range was among the worst in our experience. The resulting sound is extremely colored and inaccurate; in addition, the bass is a bit on the loose side (Q = 1.4).

Pyramid 'Metronome'

Pyramid Loudspeaker Corporation, 131-15 Fowler Avenue, Flushing, NY 11355. Metronome Model 2 + 2W speaker system, $2600 the pair.

We're told that the current production model is greatly improved over the one we tested; we certainly hope so because we didn't think at the time that the Metronome was of refer ence quality. We admired its tremendous dynamic range and its freedom from the usual gritty/spitty kind of distortions, but found its bass response rolled off and its overall sound to be lacking in the openness, transparency, airy delicacy, and definition of inner detail we expect of an "ultimate" speaker.

Frequency response and time response were constantly being traded off against each other in weekly modifications of our original test samples. We're planning to review the "final" version in the next issue.

Rogers LS3/5A Reference Monitor

International, Inc., Suite 309, 4901 Morena Boulevard, San Diego, CA 92117. Rogers LS3/5A BBC Monitor Loud speaker, $499 the pair.

This was the speaker that established the highly successful minimonitor format: clean and fast tweeter, small midrange/ woofer cone, careful attention to the crossover, tiny but very rigid sealed box. It really isn't possible to do much more with conventional dynamic speakers if you're excluding the bottom two octaves (say, 20 to 80 Hz), and the Rogers remains to this day one of the better examples of the genre. The Tangent RS2 sounds a little sweeter and better focused; the Fried B/2 and Symdex Sigma are definitely less colored; but the Rogers is the one that showed us it can be done. The day we heard it we sold our Dahlquists.

Snell Acoustics Type A

Snell Acoustics, 10 Prince Place, Newburyport, MA 01950. Type A loudspeaker system, $1370 the pair.

The ultimate embodiment of the frequency-response-is everything school of thought. The Snell is almost amplifier flat (plus or minus close-to-nothing) from 38 to 22 kHz; its -3 dB points are at 28 Hz and 23 kHz. What's more, virtually flat response is maintained over an amazingly wide angle. On the other hand, absolutely no effort is made to synchronize the three drivers in the time domain; the response is totally noncoherent. Thus, even though the sound is extremely clean, balanced and solid, there's a lack of ultimate clarity and focus. An improved version is reported to be just out as we go to press; we hope to have a chance to review it, as this is certainly not a negligible design.

Spendor BCI

RCS Audio International, Inc., 1314 34th Street NW, Washington, DC 20007. Spendor BCI vented-box loudspeaker, $700 the pair.

This is no Thiele/Small-aligned vented box; it has a +6 dB hump at 72 Hz in the composite response of woofer and vent, and it booms very audibly. The frequency response is otherwise fair, with some crossover troughs; pulse form retention is very good but with some trailing hangover. The sound is basically in the civilized Rogers/Tangent vein, but not quite as smooth and transparent; the midrange is a bit rough. Add that to the boomy bass and the speaker begins to look very overpriced.

Tangent RS2

Tangent Marketing of America, Inc., 12 Irving Street, Framingham, MA 01701. RS2 Reference Speaker, $519 the pair.

Except for its grossly underdamped bass (sealed box, +8 dB at 75 Hz, Q approximately 2.5), this is one of our all-time favorite dynamic speakers, mainly on account of its excellent deployment of the KEF T27 tweeter. The top end goes out dead flat almost to infinity (well, 32 kHz, okay?) and sounds that way, too-very open, clean and well-defined. The pulse response is outstanding, surpassed in this type of speaker only by the Symdex Sigma, and that only because the Tangent's tweeter is out of phase; you can't really call it a perfectly time coherent system for that reason. There's some ringing in a few places but nothing terribly serious. What's more, the speaker handles power quite well, making it a genuinely useful monitor, especially in view of its portability (14% x 11%" x 10").

Ultraphase 2501

Ultraphase, 2875 South Raritan Street, Englewood, CO 80110. Model 2501 floor-standing speaker system, 8596 the pair.

A rather unusual design, utilizing a staggered array of two domes and a heavily overdamped 8" woofer in an enclosure of battleship-like solidity. The result is extremely tight, though not very deep, bass and clear, well-focused, ambience-detailed sound, but with a definite edginess seemingly due to ringing.

A more sophisticated speaker has meanwhile been announced by Ultraphase; we're looking forward to testing it.

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[adapted from TAC]

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Also see:

Power Amplifier Postsurvey: Mop-Up and Afterthoughts

Various audio and high-fidelity magazines