The ESP950 is an electrostatic headphone and has been manufactured by Koss since … 1990. That makes it one of the oldest headphones still in production to this date.
Retail price is $999 but it often goes on sale for $500-700, and a Massdrop variant, the ESP95X, is currently available for $500, with new velour pads and slightly different coloring. All sets come with a matching energizer (or amplifier), the E90. The build quality is extremely poor for the price ; lot of plastic, but they’re light for the size and comfort is top notch. Most Stax Lambda models (like the Lambda Pro, SR-303 or SR-L700) are built better, although they’re also made of plastic.
○ Release : 1990
○ Current status : In production
○ Type : Over-ear / Open-back
○ Measured weight : 305g
○ Impedance : 100k Ohms
○ Sensitivity : 104dB/100V
○ Average used price : $400-600
The ESP950 is a little midcentric and sounds very smooth and inoffensive. My pair has Vesper Audio pads, that increase comfort and should help with tonal balance (lowering a bump around 1-1.5khz and improving subbass extension).
The bass is quite light even with these pads. Midbass is there, but not too punchy, very similar to an HD600. Low-end (below 60-70hz) is rolled-off, I tried as much as I could with the seal, I did not get any rumble. Bass is tight and clean.
The midrange has very good and realistic tone, most instruments don’t seem to sound off. Vocals are not very forward (not a bad thing) unlike the Sennheiser HD600. Definitely good and better than the Lambda Pro (which has leaner mids).
The treble is, like the bass, very relaxed, a bit too much to my likings. I would have prefered a few dBs more around 7-12khz. On the other hand, it’s great for people hating harsh highs. Upper-treble is also very gentle. Overall treble area doesn’t show any particular sign of sibilance or fatigue.
Soundstage and imaging are a slight step-up from HD600/6XX, but it lacks some depth and layering. My main issue with the ESP950 is that, while it sounds clean and with good detail retrieval, it’s pretty compressed in macro-dynamics. I’ve compared for hours to my HD600, and even the HD600 has better overall slam and dynamics. The polite treble doesn’t help in that regard.
Resolution and transients are quite good, considering the price of an used set (around $400-500) or the $500 ESP95X. I would not use this headphone as an allrounder, but more as a complement to planars / dynamics when I want to enjoy a smoothed and well tuned listening experience.
This a stock ESP950 measured here – not with the Vesper hybrid pads. Note the moderate 1khz bump and recession above 3khz. Bass extension, at first sight, seems good with only a roll off below 20-30hz. But I’ve never managed to hear proper subbass.