Listening #23

When I was a boy, silent dog whistles were all the rage. They were sold mail-order from the backs of comic books, alongside whoopee cushions and sneeze powder and X-ray spex. The whistles aren't so easy to find anymore, but don't read too much into that fact. Don't read into that at all.

As a child, I could understand the basic human need to torment others and see through their clothing, but silent dog whistles were utterly lacking in appeal: What was the point? The theory was interesting—that some sounds are so high in pitch that they can be heard only by animals—but the product itself suffered a basic lack of demonstrability. Maybe we can't hear the whistle because it really doesn't make any sound at all. Dogs, after all, are notoriously eager to please.

Here's a parallel: Famous doctors all agree that the upper range of human hearing is 20kHz, tops. What possible use could I or anyone else have for an auxiliary loudspeaker that extends a music system's performance out to 100kHz? More to the point, why would anyone pay $750 for such a thing?

Those questions were posed to me, in effect, when the people at Townshend Audio sent me their latest product to try: a little something they call their Maximum Super Tweeter ($1500/pair). (The name may or may not be a play on words; Mr. Townshend's first name is Max.) This is an example of a relatively new breed: an ultra-high-frequency transducer intended to enhance the performance of virtually any existing home audio system, much as a subwoofer fills a similar but diametrically different need. The Maximum Super Tweeter extends a full-range loudspeaker's frequency response all the way out to 100kHz, or so the manufacturer claims, allowing listeners to take greater advantage of the high-frequency information available on SACD, DVD-Audio, and even very-wide-bandwidth, high-resolution formats such as analog tape and the LP record. (Townshend Audio products are distributed in the States by EAR USA.)

Townshend's tweeter is a ribbon driver: a slender and extremely thin metal element that's suspended between two very powerful magnets and is driven by an amplifier through a matching transformer. (Such a driver ceases to be a ribbon if its metal element is bonded to a "host" diaphragm, at which stroke the thing becomes a planar-magnetic.) A ribbon's strong points are its general lack of coloration and, above all, its nearly perfect lateral dispersion. Its weak points are its need for a transformer—without which the very-low-impedance, coilless diaphragm is devilishly difficult to drive—and its tendency toward a sort of hysteresis distortion, given that its diaphragm is physically more well damped near to its anchor points than at its center, resulting in intermodulation distortion if driven over too wide a range of frequencies (although, in fairness, that's more or less true of all panel-type speakers). Because most of those weaknesses diminish in direct proportion to the radiating element's size, ribbon drivers are nicely suited to high-frequency applications.

The Maximum Super Tweeter is built into a stainless-steel case that's polished to a mirror finish (titanium is also available) and measures 2" wide by 1.25" high and 4" deep. The enclosure is vented, presumably to maintain a more or less constant internal pressure (heat would not seem to be an issue), and the corrugated ribbon itself is protected by a neat-looking metal grille. A peek inside shows that element to be 0.2" wide and exactly 1" long, straddled by a pair of rare-earth magnets and their respective pole-pieces, themselves physically damped with slices of dense foam rubber. The matching transformer, which is actually the largest single component inside the case, is fastened to the rearmost pole-pieces.

There's a level control on the back of the Townshend tweeter, useful for matching its performance to a variety of home audio settings. This control, actually a multipole selector switch and a series of discrete resistors, offers a choice of seven different electrical sensitivities, from 80 to 110dB/W/m. A pair of capacitors in-line with the signal complete the tweeter's very simple, single-pole high-pass filter, the -3dB point of which is said to be 20kHz (although there is still some output below even 12kHz). Another capacitor in the system appears to be used for suppressing clicks when working the selector.

All the copper in this product, including the wire in the transformer and the Litz wire in the 1.5m connecting cables supplied with it, is said to be cryogenically treated, as is the aluminum ribbon itself. The connecting cables have 4mm banana plugs at one end and "piggyback" bananas at the other: Connected as directed, the Townshend Maximum Super Tweeter operates in parallel with your full-range loudspeaker. Cables with spade connectors are also available.

Old Quad extension
I'm not sure, but I think I was singled out to review the Townshend Maximum Super Tweeter because I own Quad electrostatic loudspeakers. Quads are regarded by some engineers and hobbyists as being comparatively deficient in high-frequency dispersion, a characteristic that varies from model to model.

This dispersion shortcoming is most pronounced in Quad's first loudspeaker, the original ESL, making that model the likeliest to benefit from Super Tweeting. (It's worth noting that the near-mythic Naim FL-1 electrostatic loudspeaker, which never saw the light of day in any commercial sense and about which many thousands of words will someday be written, was essentially a spec'd-out ESL bass and midrange loudspeaker with a ribbon tweeter on top.) So, in addition to using the Townshends with my own Quad ESL-989s, I wanted to try them on a pair of original Quad ESLs. I was even more anxious to hear what a dyed-in-the-seersucker ESL veteran might think of them, so I turned to my friend and fellow Upstate New Yorker George Stanwick, proprietor of the audio distribution firm Stanalog—a man who has owned and enjoyed Quad ESLs for as long as I've known him (footnote 1).

I brought the Townshend tweeters to George's house for a morning of comparisons. Although I'm not familiar with most of the supporting components in his system, my goal that day was simply to hear if and how the Maximum Super Tweeters changed the sound when added to his Quad ESLs. To that end, George and his associate, Francis Milano, went to work setting up the Townshends. (Francis deserves extra credit for a mounting arrangement that held the tweeters atop the centers of the main speakers, more or less at ear level, while also providing a measure of immunity from intermodulation effects from the main speakers.)

With the tube amps warmed up and the tweeters in place, we settled back for a morning of Dylan and Elgar—the latter represented by a clean copy of that magnificent Dream of Gerontius by Sir Adrian Boult and the New Philharmonia (LP, EMI SLS 987). Without putting words in anyone's mouth, it's safe to say we were all impressed. The tweeters sounded best with their level controls turned to 2 or 3 (within a range of 1-7), at which they contributed a near-perfect dose of texture, color, and spatial believability—the latter by virtue of extra "air" and ambience. We all agreed that singing voices gained the most in realistic tone and sheer presence, although the three of us were equally impressed at how the Super Tweeters enhanced the presence, and even the apparent dramatic range, of the large orchestral drum in the Elgar recording. At the same time, no one expressed any negatives: for my part, although I wondered if the Townshends might also reveal more in the way of grain or surface noise in that unfamiliar (to me) context, I heard nothing of the sort.

Back home on Turkey Buzzard Hill, things were mostly the same, albeit with a few key distinctions—all apparently related to the fact that my Quads and George's are very different things. In the original ESL, high-frequency propagation, such as it is, is handled by a narrow strip of a central diaphragm: Thus, to the extent that it's capable of dispersing high-frequency sounds at all, the original Quad does it in much the same way as any ribbon, with much the same pattern of dispersion. By contrast, my Quad ESL-989s use an annular ring pattern of stators, intended to mimic a point source rather than a line source—the highest frequencies thus emanate from a small area at the center of this comparatively large loudspeaker.



Footnote 1: The suggestion by a handful of beskirted biddies that audio reviewers must never have audio manufacturers as friends is laughable, beneath contempt, and ultimately quite sad.—Art Dudley
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