Koss ESP/950 electrostatic stereophones Page 4

To prepare for this project, we had scheduled an early October session to select the microphone and its placement. David Manley of VTL/Manley and his wife flew out from California to deliver his Manley Gold Reference Stereo Microphone— a crossed figure-eight design that was one of the prime candidates—and Ed Meitner of Museatex drove down from Canada to bring his FET mike preamps. I felt that this would be a first-rate opportunity to compare the Stax Signature and the Koss ESP/950 with the live event present for immediate comparison. The live event in this instance would not be Robert Silverman and the 9' Steinway to be used in the final sessions, but the church's 7' (est.) Yamaha and a local pianist.

While RH and JA set up the prime recording equipment and fussed with mike placement, I set up both sets of headphones in the recording equipment room—actually the sacristy off the main sanctuary. While the recording was going on, I moved back and forth between sanctuary and sacristy, listening to both the live instrument and the headphones.

First, a few interesting, and not really surprising, general observations. One can never know exactly what the microphones are picking up in any given situation. Even ignoring the fact that mikes and ears do not respond in the same fashion, you can't get your ears into the same acoustic space as the mike—the best you can do is a few feet away. I stood just under the Manley stereo mike (or just between a pair of spaced B&K omnis also under consideration) in making my assessments. Moving only a few feet back, to the first row of pews, significantly altered the tonal balance, reducing the "weight" of the sound.

Most of my observations were made with the Manley mike, which saw the most use and is, at time of writing, the prime contender for use in the final recording sessions (footnote 6). Initially, the headphones were connected at the output of the Ampex, and were thus responding to the sound off the tape, not the direct mike feed. In this configuration, the Kosses sounded decidedly warm, the Staxes far more open through the mid- and upper-bass region—and thus more open-sounding overall. It then occurred to me that analog tape decks, even very good ones, tend to have "head bumps" in their low-frequency responses, especially at the higher speeds desirable for the best overall sound. I asked RH what the low-frequency response of the Ampex was at the speed we used (primarily 15ips). He indicated that there was a broad 2dB rise centered at about 60Hz. Voilà. That was, I estimated, just about where the Kosses were sounding too fat.

Fortunately, the Meitner mike preamps had two outputs—balanced outputs which were being used to drive the recording equipment, and unbalanced outputs which were not being used. Fortunately the interconnects I'd brought—about 20' of AudioQuest Lapis—were long enough to reach from the preamps, situated in the sanctuary, into the sacristy. I transferred the drive for the headphones to the direct mike feed.

Result? Major improvement in the sound of the Kosses. They were still full-bodied, still warmer and richer than the Staxes, but there was now no lack of clarity or detail through the mid- and upper bass.

The question still remained, however: Which set of headphones was the more accurate? My final conclusion came down on the side of the Staxes, but it was not without some degree of uncertainty. The Kosses seemed to err slightly on the warm side of neutral at the low end, while the Staxes sounded a bit leaner than the live piano. The top end of the Kosses seemed closer to what I was hearing from the piano itself, with the Staxes slightly emphasizing air and ambience. But one additional variable—difficult to judge precisely—seemed to tilt the balance in favor of the Staxes: the sound of the Manley mike. Judging from how it compared with the sound of the B&K omnis, it would seem to have a trace of leanness in the bass. David Manley also indicated that, like many condenser mikes, it has a small rise on top—perhaps +2dB at 12kHz—resulting in slightly lean bass and a slight increase in top-end air.

This sounded very much like my impression of the Stax headphones compared with the live sound. The Staxes thus appeared to be telling me what the mikes were picking up. The Kosses, in contrast, were just a bit sweeter, warmer, and more forgiving—the same impression I had received from a variety of commercial recordings.

The Staxes, with their dedicated tube amplifier, offer a greater perceived value than the Kosses with their small, unassuming energizer. But I've already indicated that there's more to the latter than meets the eye. Still, the Koss energizer/amplifier can service but one set of headphones, in contrast with the Stax amplifier's three outputs. And I could not help but wonder if the E/90, with its 63dB of gain, was of the same sonic caliber as the Staxes' tube amp. There is, unfortunately, no way of knowing; neither junction box is compatible with the other maker's headphones.

The Koss ESP/950 is an exceptional product. It is just slightly euphonic at the frequency extremes compared with the similarly priced Stax, but its overall sound, in particular its ravishing midrange, puts it in the top class of headphones. It is unfailingly musical, and, disregarding the whole issue of headphones clamped over the ears, generates less listening fatigue than any other transducer I can think of. There were a few quirks in its operation (the matter of the junction box is still open to possible update), but on sonic grounds I can't recommend it highly enough. As much as I respect the Stax Signatures—and I would likely reach for them first if I wanted to analyze a recording or line-level component—for pure musical pleasure the Kosses are easily their match, and perhaps more. There are so many variables in headphone listening that a potential buyer should certainly audition both.

Footnote 6: Ed Meitner, who doesn't fly, had planned to bring down a custom mike he's working on, but it wasn't ready in time for this dress rehearsal.
Koss Corporation
4129 N. Port Washington Ave.
Milwaukee, WI 53212
(414) 964-5000

ndimoff's picture

Another great news is that the electrostatic transducers of the Koss'es do not age. Bought my pair in April 1993 and they still sound as new. In comparison, the panels of my Martin Logan Aerius electrostatic speakers need to be replaced every 5-7 years.