Listening #37 Page 2
Yoshi Segoshi was so impressed that he eventually decided to design and build a loudspeaker using the Hartley 220 MSG. The result of his work, which he calls the Hotei, is now a commercial reality—and I've been enjoying a pair of them in my home for a number of weeks.
The driver in question is a 9" full-range coaxial design in which the outer edge of the high-frequency "whizzer" cone is almost flush with the larger "woofer" cone (which is to say, the former doesn't stand proud of the latter, as with the Lowther drivers). A precise amount of compliance is built into the join between the two, and that helps prevent intermodulation distortion. The cones, made of Hartley's proprietary polymer, are built on a fabric host, and the surround has the seemingly contradictory qualities of being integral and being much more compliant than the cone. As Richard Schmetterer explains, it's all in the way the cone is made:
"Unlike a vacuum-molded cone, our polymer is added to the mold as a liquid. It's built upward, from the voice-coil area, and when we get to the perimeter, we switch from our polymer to a silicone rubber. That can only be done slowly, by hand—but it has great advantages. With a glued-on surround, a driver will exhibit unwanted resonances where the two materials are joined, but ours acts like it's one piece. Also, most surrounds have a longevity problem, but our silicone rubber doesn't: It isn't affected by ozone."
The Hartley 220 MSG is built on a cast-aluminum frame, and its 6-lb ferrite magnet is also built and energized in-house. As Richard Schmetterer says, "One of the last things Dr. Luth accomplished for us, back in 1980, was figuring out how to do 3-D mapping of the flux lines in a magnet structure. He used that information to devise a way of tooling a magnet assembly—the pole piece, inner and outer plates, and core—in which the flux is consistent all the way through, regardless of the voice-coil position."
The Hartley company calls their proprietary magnet configuration an EFM, for equalized flux module—although, as Schmetterer admits with a laugh, "We came up with that during a time when most audio companies had to have short, catchy names for every breakthrough." Hartley doesn't publish free-air resonance or efficiency specs for the driver, but they do say that it has a peak-to-peak excursion of 3/8"; that makes for another interesting comparison with Lowther's full-range drivers, which seem hardly to move at all under most conditions.
For his Hotei loudspeaker, Yoshi Segoshi mounted a single 220 MSG in an aperiodic cabinet with a volume of approximately 90 liters. The cabinet walls are made of 1"-thick MDF—except for the internal bracing, the rear panel, and the wooden grillework that protects the rear-firing resistive port, all of which are solid maple. Concentric-rib Deflex panels are glued to most of the interior surfaces, and the exterior is finished in semigloss water-based lacquer, with the front baffle painted to match the Hartley cones themselves, using a cream-colored alkyd enamel—a striking touch.
Segoshi augmented the Hartley driver's treble performance with a supertweeter: the Chinese-made G2 aluminum ribbon from Aurum Cantus, which combines good sensitivity (96dB) with a tube-friendly nominal impedance of 8 ohms. In the Hotei, the Hartley driver is driven directly, while a single-pole high-pass filter is wired in series with the Aurum Cantus ribbon. The filter puts the ribbon's response 6dB down at 10kHz and 12dB down at 5kHz.
Partly because I'd never encountered a Hartley driver before and partly because I felt bad for not having used my Audio Control spectrum analyzer in such a long time, I decided to measure the Hotei. I began by disconnecting the ribbon supertweeters and taking a series of nearfield measurements of the 220 MSG, over a 90° range. I saw that the loaded driver's response was flat over most of its range, with high-frequency dispersion dropping dramatically as I moved off-axis—which wasn't surprising, given both the large size of the treble cone relative to the wavelengths of the tones it was being asked to play, and the lack of any phase plug. What did surprise me was a pronounced response dip centered at 6.3kHz. Again, I couldn't help but wonder if that was due to cancellation effects near the apex of the tweeter cone, the likes of which might be corrected with a phase plug—but I could see no easy way to test that theory short of fastening some manner of strap-on plug to the cabinet itself. Which would be a little too kinky for my tastes.
When I put the Aurum Cantus supertweeter back into the mix, it certainly did no harm—the notch didn't get any worse, I mean. In fact, it added another octave and a half of usable treble response.
Moving the microphone to the listening area gave additional evidence of the limited treble dispersion: The Hotei must be aimed directly at the seated listener in order to give its all. While I was playing around with the spectrum analyzer, I decided to see what difference, if any, was made by the foam plug and wooden grille that comprise the Hotei's resistive port. I was impressed—not only because the difference was measurable, but because that aspect of Segoshi's cabinet design provided an unambiguous smoothing and flattening of the upper-bass and lower-midrange portions of the curve. Good show!
Safe at home
Some of the above is disingenuous, of course: I'd spent a long time listening to the Hotei before I ever dreamed of measuring the speaker.
It turned out not to be as friendly to single-ended-triode (SET) amplifiers as I'd hoped it might be. I admit to assuming that any amplifier from outside the norm these days is a low-power one, and that any similarly radical speaker is on the high side of the sensitivity scale. But my 3W Fi 2A3 didn't quite swing with the Hotei. Then again, my 20W Lamms managed nicely.
It's also safe to say that some audio perfectionists would be put off by the Hotei's upper-midrange coloration: That 6.3kHz suckout is just about as audible as the measurements suggest, and the result was a sort of hollow sound that was noticeable with recordings of solo singers. Listening to familiar voices, especially on studio pop recordings lacking in natural ambience or room sound, I couldn't shake the image of people singing through cardboard tubes: Well, it wasn't that severe, but it did have a bit of that quality.
Instrumental music fared much better. Even when I heard the Hotei skew the timbres of instruments I know well, it was easy to overlook that shortcoming in favor of the speaker's considerable strengths. In particular, the Hotei—and so, I assume by default, its Hartley driver—shared a quality with the best of the old-style Tannoy loudspeakers I've heard: The more percussive a musical sound was, the more realistically it was reproduced. Snare drums came alive, not just in a barking, obvious sort of way, but with rich, convincing textures. The side drum in Nielsen's Symphony 5 harangued me the way it should, and after several spins, the vibes in Neil Young's "Will to Live," from American Stars 'n Bars (LP, Reprise MSK 2261) always managed to startle me a little. Even plucked strings leaped out with greater force than I'm used to—as in the second movement of the Ravel String Quartet in F, played by the relentlessly compelling Cypress Quartet on their own label (CD, CSQ 3275).
And though I'll never be a stereo imaging freak in the normal sense, I do respond well to good spatial performance—and in that regard I thought the Hoteis had superb wholeness and presence, in much the way that good SET amps have those qualities. I spoke to Yoshi Segoshi about it. The way he hears it, "The problem with most modern speakers is that they create their own space—a phony sense of air—and then put the music into it. On the other hand, drivers like the Hartleys put the music into the same space as the listener."
I agree completely. And while the Hotei's unique combination of strengths may not be to everyone's taste, I think that virtually anyone who's capable of responding to passion and intensity in recorded music would be charmed by the way this speaker plays Ike Quebec's "Me 'N' You," or Sonny Rollins' "Tenor Madness," or even Norman Blake's "Green Leaf Fancy."
Never forget that high fidelity, the concept for which we may or may not have H.A. Hartley to thank, encompasses a great many attributes, just like music itself. An audio product can succeed or fail at doing any number of things well, and the decision of how to rank those aspects of its performance can be made only by you. Keep that in mind when I assure you that, despite its flaws, Yoshi Segoshi's Hotei and its Hartley driver tell a crucial part of the truth.