Massdrop x Koss ESP/95X

Massdrop x Koss ESP/95X Review

Sound Impressions


Sadly, the electrostatic headphone pool is not fraught with bass head levels of low end. If you like bass, of course, the ESP/95X offers great quality, but a relatively low to moderate level of a physical quantity, even when boosted.

I recall, back when I owned the Stax 007 Mark II, that I had owned the bassy edition of the headphone and still felt like it wasn’t nearly bassy enough. I feel the same about this 95X.

No matter what I do, I cannot squeeze out enough bass to justify how good the quality is around it. I yearn for much more. I would rate the physical quantity as right on the cusp of the line of bass light and bass moderate. This is no K7xx series from AKG where it is very bass light, this ESP/95X has more bass than that on a stock flat EQ.

Electrostatic bass is just so gooey and fast, so smooth, that you tend to want a bit more out of it to match something like the bassier variant of the Stax 007 (my favorite TOTL headphone) and that is something I wished for nearly 10 years of owning the original Koss ESP950. I wouldn’t worry about quality, for the price at $499. This is a steal.

Back in 1990, when the ESP/95X was really first released, we didn’t even have proper musical sources to justify the quality the ESP950 could offer you. Meaning, the music sources, and files were subpar and limiting the potential of the ESP950 for nearly another 10 years or so after its release.

Bass Tonality

The low end of the ESP/95X is very pure. Yes, I regard it as a clinical tone headphone akin to the other electrostatics out there in this area of the experience. It is very fast, very clean, very pure feeling and most of us years ago thought the $999 was good for a “cheap” Electrostatic rig.

Today, at half that price, this is even better in my mind now. I am real, real snobbish when it comes to things I would buy, and for this price, I’d actually buy the Drop Koss ESP/95X system and would recommend it to anyone with half a grand to spend on a complete amp and headphone system.

And with that in mind, the bass tonality far exceeds that of any other $250’ish headphone. I say that, because look, you get the amp and the headphone for this price, so split it. And you get the ballpark value for the headphone by itself.

What other headphone for $250-499 offers this type of buttery smooth feel in tonality? Scratch that. What headphone under $499 is even electrostatic, to begin with?

Massdrop x Koss ESP/95X

Mids and Vocals

The ESP/95X system is not overly forward sounding, it does lean back just a bit so that the vocal experience does not appear to be supremely mid-forward. Although, I do still consider it well into the mid-forward sense of appeal.

As far as tonality goes, the ESP/95X is a killer at $499. In my opinion, there aren’t that many other headphones that offer anything remotely close to the level of slick smoothness that this ESP/95X offers for the price. That electrostatic effortlessness is in full blossom here and with regard to vocals, the experience is extremely yummy.

The headphone is actually just a bit warm on the lower mids, which is a bit odd to me because the bass is more along the lines of a clinical appeal, at least again, to my ear. This makes the bass end sound completely separate from the lower mids, only very expensive headphones tend to offer this type of physicality.

With regard to the raw purity factor, the ESP/95X and Energizer is the only rig I could test with since I don’t have a custom adapter to use on any other Electrostatic amplifiers. So, what I have is all I can discuss.

Mids Purity

The purity factor is good, not great. I detect a bit of grain and a slight sense of a muffled sound, but again, these headphones came out in 1990 and have been a staple ever since. I would place them on par with the Sennheiser HD6XX in raw quality in the midrange, however, that is where the bus stops for the night.

The upper treble is just a bit nasal and lacking clarity that I would want in a great mid-fi headphone. Again though, I don’t fault it. At this new price, it is still pretty good. But mid-fi has evolved and moved onward, improving on what is available even at the $499 tier.


I consider the entire top end overly muted and lacking sparkle. I also consider it a bit grainy as well, which doesn’t mesh with the lacking upper midrange that I was just speaking about.

To be blunt, the 950 headphone lacks engaging quality in the treble regions. I do not feel the treble is reflective of the $499 price tag and I certainly never felt the $999 former price tag of the original was justified for the treble offered either.

Regardless of the source music files or player connected to the Energizer amplifier, I can’t swing the treble into what I feel to be something I would actively want to hear for long periods of time.

The top side engaging factor is lacking, but wow is it smooth. Again, you likely aren’t buying the ESP/95X for the raw purity factor. You are buying it for the fantastic tonality and physicality aspects that Electrostatic headphones tend to offer.

That effortless and lightning-fast quality is present on the ESP/95X and yes, despite it being a little lacking in quality/purity factor, the smoothness factor is hyper addictive. I instantly need that back when I stop listening to the ESP/95X and swap to something non-electrostatic in type.


The ESP/95X does not offer a wide image effect. Instead, it is coherent and tall, very suitable for vocals and not for live recordings. Those who enjoy jazz standards and light rock will enjoy this soundstage.

I am not overly fond of using the ESP/95X for Classical needs, although, the quality overall is just fine for it. I feel the physical shape of the ESP/95X offers a taller than wide sound effect to the imaging void and that doesn’t really mess with live recordings or orchestral tracks.

However, it does mesh with Podcast and general YouTubing, which I absolutely adore the ESP/95X for. That effortless appeal and smoothness factor, combined with the intimate vocal setup, is absolutely to die for when surfing the Net, or even playing Single Player video games.

I frequent games like Borderlands and The Witcher 3 and I could not be happier. True, the depth of field is just so so, but, again, you almost forget about it due to the Electrostatic tone that is buttery-smooth from top to bottom.

Massdrop x Koss ESP/95X

Select Comparisons

Sennheiser HD800

Okay, it is a big stretch of a price there between these two but still should be fun to at least know about if you heard or own the HD800. The latter is extremely wide, very thin sounding, housing even less bass quantity than the ESP/95X.

However, the ESP/95X trumps the Sennheiser in tactility and density factor. Where the HD800 feels more sharpened, the Koss feels smoother and easier going.

Of course, the Koss is not on par in quality anywhere, but I do instantly miss the Koss when I swap back to the HD800, due to the very addictive flavor of Electrostatic presentation in general.

Stax 007 MKII

The black version of the 007 is my favorite of the three available, it is the most bassy of the variants. And for that reason, it is actually the least clear of them all as well. Naturally, the quality of the Stax 007 is leagues beyond the Koss, but the ESP/95X retains a similar entry-level point of that same buttery smooth appeal.

Electrostatics are just the alphas when it comes to this type of tonality. Yes, I think the MKII is warmer and bassier, which makes it feel thicker and a little bloated compared to the less densely packed ESP/95X. The problem here is that the 007 costs just as much to amplify as it does to buy the headphone, maybe more. Whereas the ESP/95X comes with everything you need.

Massdrop x Koss ESP/95X

Our Verdict

True, the ESP/95X build quality is lacking, but the presentation is glowing. At this price, this is a champion of a deal. As mentioned, I paid double this price a decade ago and felt like it was still a good deal even back then.

The Koss Drop 95X system includes the Koss Energizer amplifier, so drop in a half-decent DAC or portable source and pair them together. The result will be one of the best mid-fi headphone rigs you can get. I am beyond happy about those new velour pads, they are much better than the old stock Koss pads.

Overall, the Massdrop x Koss ESP/95X is a great electrostatic headphone. It is not the clearest you can get today for the price, but it is perhaps the cheapest complete rig system you can get that will let you step into the world of Electrostatic tonality. And trust me, you likely won’t want to leave it.

Massdrop x Koss ESP/95X Specifications

ESP/95X Electrostatic Headphones

  • Acoustic principal: Circumaural open-air design with minimal acoustic damping
  • Diaphragm: Ultra-low-mass 1.5-micron C-grade polyester film coated with semiconductive material
  • Diaphragm radiating surface area: 7 sq in (45.6 sq cm)
  • Frequency response: 8 Hz–35 kHz
  • Headband: Stainless steel, extendable
  • Headband cover: Wide leatherette-style vinyl with 12mm-thick polyethylene foam padding
  • Yokes: Horizontal and vertical pivoting with integral headband lock-and-detach mechanism
  • Cushions: Velour-wrapped foam
  • Cup size, including cushions (H x W x D): 5.9 x 3.9 x 1.6 in (15 x 10 x 4 cm)
  • Cable: Straight, dual entry, 4 ft (1.2 m) with 6 ft (1.8 m) extension
  • Weight: 12.45 oz (353 g)

E/90X Electrostatic Energizer

  • Frequency response: 1.6 Hz–50 kHz (-3 dB), 100 Vrms differential output
  • THD + N: 0.001% at 1 kHz, 100 Vrms differential output
  • Input impedance: 100 kohms
  • Input level: 1 Vpk (for full power output)
  • Voltage amplification: 60 dB
  • Audio output voltage: 790 Vrms differential; 2,200 Vpk-pk differential with soft limiting
  • Channel separation: -80 dB at 1 kHz, 100 Vrms differential output
  • Signal-to-noise ratio: -100 dB at 100 Vrms output
  • Bias voltage supply: 600 VDC
  • Signal polarity: Absolute phase (non-inverting)
  • Volume control: Dual concentric continuous audio taper high-quality potentiometer with split shaft for balance
  • Switch: Power on/off rocker
  • Input jacks: RCA type (left and right), 3.5mm stereo, AC/DC adapter
  • Power: AC adapter power supply for E/90X (included, select 120V or 220V)
  • Power consumption: 320 mA DC current at normal listening levels
  • Dimensions (H x W x D): 2.6 x 4.3 x 6.1 in (6.5 x 11 x 15.5 cm)
  • Weight: 17 oz (482 g)

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