Koss ESP/950 electrostatic stereophones

Love 'em or hate 'em, headphones serve a purpose. My first headphones were Kosses, and they were perfect for use in a college dorm. While I've always owned a pair or more over the years, somehow they never became my primary mode of listening, except in situations where using loudspeakers at satisfying levels risked eviction, bodily harm, or both.


Because of their small size and the low output levels they're required to produce—which, because of the close proximity of the ear, can generate prodigious, even hazardous listening levels—designing a good pair of headphones would seem to be a trivial exercise next to the challenge of filling a room with loudspeaker sound. It isn't, of course, and headphones have never generated the kind of interest or devotion that loudspeakers do. Has the world of audiophilia demanded a Headphone Builder magazine? Do people flock to Stereophile shows to check out the latest development in headphones? Can you name a famous headphone designer? No—except perhaps for John Koss, who can certainly lay valid claim to bringing headphones into the world of high fidelity back in the early 1960s. But even he could not make the headphone challenge the loudspeaker.

The reasons, of course, center on the fact that headphone listening is a distinctly different experience from listening through loudspeakers. First, it is a decidedly solitary activity. Second, headphones can be uncomfortable, even claustrophobic for some listeners. Third, although headphone listening frees the listener from the minefield of room acoustics, it has a variable of its own: the cavity formed by the ear canal and the headset. The outer ear, or pinna, may or may not be a factor, depending on the design of the headphone, how much of the ear it encloses, and whether or not it disturbs the ear's natural lay. Therefore, listening to earphones involves certain user-dependent variables just as significant as the loudspeaker-room interface.

Then there's the actual quality of the sound presented by headphones. The best headphones can provide detail far more clean and precise than even the best loudspeakers, although that detail can be a mixed blessing. On the downside, I have found that, in general, headphones do not convey the power inherent in certain types of music as well as the best loudspeakers, nor do they often provide a truly convincing soundstage. More about the latter further on, but the matter of acoustical power is an unavoidable physical fact. Loudspeakers move air, lots of it, and often provide physiological cues other than through the ears; headphones cannot.

Despite these drawbacks, headphones have important applications. There is a bewildering variety available—just ask Bill Sommerwerck, who spent much of 1990 scoping them out for his monster headphone survey in Vol.14 Nos.3 and 8 (March and August 1991). But the best of the breed, in my experience, have always been electrostatic in design. The principle here is the same as in electrostatic loudspeakers, except on a smaller scale. And with headphones, the electrostatic design and use challenges of power output, dispersion, and placement are neatly avoided.

Koss has been making electrostatic headphones as long as anyone, beginning with the ESP/6 in 1968. I still own a pair of the later ESP/9s, which unfortunately shared a disadvantage common to many early headphones—they were heavy. I haven't used them for years. The new Koss ESP/950 is a different animal altogether. Like its ancestor, it is a circumaural device—meaning that it encloses the outer ear completely within its padded earpiece instead of resting on it. But it is an open-back headphone, a feature it shares with most of today's electrostatic headphones and which eliminates, for all practical purposes, potential box colorations created by the sealed rear chamber of fully enclosed 'phones. Though the complete enclosing of the ear means that the rear radiation from the ESP/950's earpieces cannot cancel the front radiation (the side facing the ear cavity), it also means that sound will radiate into the room. It isn't very loud, but your taste in music will remain no secret to others in the same room (footnote 1).

The ESP/950 headset is extremely comfortable, even for those wearing eyeglasses. The earpads are high-quality vinyl of a soft, almost glove-leather consistency. They seem to breathe well, but I never had the opportunity to use them on a hot, sticky day, the latter being almost nonexistent here in Santa Fe (hot, yes; sticky, no). The headset is lightweight, seemingly a bit lighter than that of the similarly priced Stax SR-Lambda Signature T1. The headband adjustment is convenient, the only problem being that the earpieces do not swivel at all (the Staxes' do). I had no trouble with fit despite this, but each user will have to determine for him/herself if a comfortable fit is possible.

The earpieces connect to the small E/90 energizer/amplifier with a 47" cord; a 6' extension is provided. The energizer is a deceptively simple device with a front-panel volume control (with concentric, friction-locked controls for left and right channels). The front panel also sports a power switch, LED power-on indicator, a socket for the headset connector, and a stereo minijack input. The latter is in parallel with a set of RCA input jacks in the rear. The only other feature on the back is the socket for the 9V DC drive provided by one of those ubiquitous plug-in transformer/power supplies that you probably have a drawerful of at home.

Footnote 1: Those of us who have to walk though TJN's office to get to our own can attest to his tastes in music, thanks to the Kosses.—JA & RL
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.