Koss ESP 950 Review

Koss ESP 950 Review

One of the designs we’ve conspicuously avoided reviewing here at MajorHifi, electrostatic headphones have a reputation for quality and lack of portability.  But as we’ve seen our audience grow from casual consumers to more engaged enthusiasts, we’ve realized that more and more people may indeed be interested in finding out what all that fuss is about.

The Koss ESP 950 isn’t a new headphone.  Perhaps shockingly, it was introduced in 1990.  And yet, after a quarter of a century, this $999 headphone is a phenomenal piece of engineering – and the perfect introduction to electrostatic sound.

Koss ESP 950 Review

Koss ESP 950 Review

The ESP 950 comes in a nylon case roughly the size of your standard cinder block.  Inside, there is a power transformer, an optional battery pack (for portable listening, I guess), and a wide selection of audio cables – including standard 3.5 mm stereo and RCA connections.  The headphones come in sections, requiring you to attach the earpieces to the headband and extenders.  This is done with the press of a button, and was alarmingly easy to do.

The power transformer is necessary to overcome the nominal impedance of these headphones, and it functions much as your standard amplifier would.  Input can be either RCA (located on the back of the unit), or the more widely-available 3.5 mm stereo input (located on the front of the unit).

A single knob on the face plate controls volume between the left and right channels.  This can take some getting used to, but it’s definitely preferable to the setup I’m used to – the ability to fine tune left and right ensures you can tailor the sound for your own ears.

Construction seems too plastic and too lightweight to ever be considered “good.”  But the more time I spend with these headphones on, the more I can appreciate the design.  It’s incredibly light on the ears and doesn’t press down on the top of your head.  You could probably live in these headphones if you wanted to.  I do.

Cabling is thick and robust.  If you can damage it, you deserve an award of some kind.

The portable battery pack runs on 6 1.5 volt C-size batteries.  I don’t know who would ever use this battery pack, or why; the transformer, though light, is still bulky.  I doubt anyone is taking it with them on their morning commute.


Frequency Range:  8-35,000 Hz
Impedance:  100,000 ohms
Sound Pressure Level (SPL):  98 dB
Total Harmonic Distortion (THD):  NA

The specs reveal a wide frequency range with plenty of detail in the lows and highs.  Perhaps the most glaring oddity about these headphones, the massive impedance requires the included power transformer.  That being said, the volume is consistent with most other open-back headphones from manufacturers like Sennheiser, Grado, Audeze, or Hifiman.  Finally, a measurement for distortion is given by Koss, and I’m not even going to guess a number.  Whatever they’re doing here, it is mesmerizing.   Even if I could guess a number, the actual number would probably be far lower.  This is one of the cleanest sounding headphones I have ever heard.

Low End

There might be some slight bleed in the low end of the ESP 950.  Or maybe my test tracks have finally met their match.  Maybe my test tracks are complete rubbish and only the 950 has been able to show me as much.  Regardless, the slight bleed I hear in the low end is the only blemish there.  The rest of the low end is clear, with an exacting level of detail.  As with most electrostatic headphones, the ESP 950 is light on bass, but the sound is so good that I don’t really miss it all that much.


The midrange is characterized by an arresting sense of fidelity.   It doesn’t matter what you are listening to, when you hear these mids, you’ll know:  this is the way music should sound.  Vocals and instrumentation are equally reproduced, without an iota of distortion or compression.  Compared to other headphones, the sound seems meatier, more substantial.

High End

Bright with details that sparkle in your ears, the high end of the 950 drips fine detail.  This detail extends into the highest of high notes.  While never quite reaching piercing proportions, the sound renders instruments and vocals with complete accuracy.  Violins, especially, benefit from this rich and unparalleled high end.


Listening to the ESP 950, I have the distinct impression that I’m surrounded by instruments.  This is truly an immersive experience, no doubt helped along by plenty of depth and good placement.  Paired with the open back design, these traits result in a sound that seems almost tactile.

Other Observations

Greater amounts of volume seem to shift the sound profile toward a more dynamic shape, with high highs and low lows.  Or perhaps my hearing just benefits more from the increased volume.

The longer I go on listening to these headphones, the less I remain unbiased.  These things are fantastic.  For classical, for rock, for pop, for hip hop…these headphones offer a sense of clarity I haven’t seen in other models.  The sound never seems to colored or adjusted – just full of detail, on every track.


Let’s keep this quick, so my growing love for these headphones doesn’t impede my desire to stay a straight shooter.  Folks, if you’re in the market for headphones, and poking around the $1000 price point, the Koss ESP 950 is obviously a headphone worth considering.

Anyone who prefers more bass in their sound would do well to also consider the Audeze LCD-2.  With a wider frequency range, the sound might seem more dynamic – at the cost of less detail.

Those who prefer a brighter sound with more emphasis on the high end could keep the Grado GS1000e in mind.  Utilizing maple wood in the earpieces, this headphone sports more treble than other models.  Of course, like the LCD-2, the GS1000e won’t offer anywhere near as much detail as the ESP 950.

Which pretty much brings me back to what I really want to say to anyone reading this review:  Don’t just read this review and rush out and buy these headphones.  That’s stupid.

A headphone this fine needs to be listened to.  It needs to be handled, played around with.   You need to pair it up with your favorite test tracks and experience this sound for yourself.  Because it is an experience.

Final Analysis

Some headphones age like milk.  The Koss ESP 950 has aged like wine.  At 25 years old, this feat of audio engineering continues to hold up in comparison to newer, flashier models.  If a lack of detail is your problem, this headphone is your solution.

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Carroll is a headphone junkie residing in Brooklyn. He's a huge fan of Grado, UK hip hop, and the English Language in general. When not testing audio equipment or writing, you'll find him taking photographs or fiddling with circuit boards. You can contact him at carroll@majorhifi.com.