Massdrop x Koss ESP/95X Electrostatic System

General Information

Massdrop x Koss ESP95X Electrostatic System.png

"A revival of the standard-setting ESP/950 released by Koss in 1990, these headphones bring electrostatic quality into a whole new price bracket."

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Fast yet at a cost
Pros: -Warm sound signature
-Light and comfortable
-Easy to listen
-Best entry level electrostat system IMO
Cons: -Dynamics are compressed
-Recessed subbass

Thanks to r/headphonelibrary for supplying this tour unit. @Mshenay is the one who runs it so thank you for having this tour avaliable which recently started again in January 2021.


The Koss ESP 95x comes with an e/90x energizer and AC Adapter, 3ft RCA to RCA cable, 2ft 3.5mm to 3.5mm cable and 6ft extension cable.

Fit and Comfort

Comfort wise, I say these are probably the most comfortable headphones I ever tried. It just feels so light on the top headband and does not create any hot spots. The clamp force is a bit light though which I do not mind but at the same time it falls off my head if I am not in an upright position. The pads have a stiffer foam material but not to the point where it could cause comfort issues.


The build for the most part is pretty much plastic from what I can tell besides the part that controls the headband’s extension. It really reminds me of Stax ear speakers I used to own but the build quality on the Koss I would say is better and more held together. I do not have much of an issue with this as you do get a light, comfortable headphone which I can not say many other headphones are anywhere near as comfortable. I do like that you can easily take this apart and replace the headband if needed. The energizer itself is pretty compact as well being about 6”x4.5”x3” and feels light. Also seems to just be plastic and the knob does have an option to change the volume from the left channel and right channel. I think this can be useful as electro stats can sometimes have one side going quieter over time when not properly taken care of.

I also did not notice any creaking noise while I did use this. So that was not really much of an issue for me.

Sound Leakage:

Tried to volume match to what my other headphones I have, and I would say the sound leakage is above average in terms of how much everyone can hear around you. Something like an HD 6xx series or HD 800 would leak less than this, but it is not as bad as a Stax lambda or Ananda.

The sound:

I guess if I were to summarize the sound, I would say recessed sub-bass, recessed lower mids, slightly shouty upper mids, but warm on the treble.


I ended up using SDAC-Balanced ->E/90x energizer on foobar2000 with flac files.


So, this follows a similar feeling in the sub-bass to what most electro stats sound like. I tried some sub-bass tests such as A1 2019, and massive attack angel, and for the most part the sub-bass sections were whisper quiet and there was not much of sense of rumble. I tried to EQ in sub-bass and happy to say it does EQ well, but the amount of EQ it needs for my taste is a bit more than I would be comfortable using. I would say in the +10db range to somewhat get a sense of rumble in these songs and towards my preference. The mid-bass to upper bass has a bit more body in comparison but I still sort of find it a bit recessed. The decay on the bass is fast as well. Overall, really what you expect out of an electro stat but maybe a bit better than Stax’s offerings in this range.


The mids on the other hand seem a bit more balanced than the other Stax products in this price range. The lower mids do seem a bit recessed where I would be EQing in a few db in to give it more body, usually I prefer more emphasized lower mids. The other part is that the upper mids can be a bit shouty but not anywhere near as bad as stax lambdas can be. I find the part to be well done by Koss versus Stax’s lambdas as they maintained a somewhat inoffensive and relatively balanced signature. I did not really need to tweak the upper mids too much versus but a few db down on 1.5k were nice to have.


So, I believe my favorite part of this headphone would be the treble as it can be mostly warm and easy to listen to. The treble is pretty much warm throughout it all. I did have an L700 and it just sounded so bright in comparison, the ESP 95x really makes it a lot nicer to listen to. I did notice that were some peaks on 9k, 11k and 13k and made it sound just a bit airier than what I am normally used to. Although to me it does not feel extreme, I just lowered those parts by a bit.


So, like most electro stats I heard, the macro dynamics are just really compressed sounding, especially in the bass. I would say these are about as compressed as the L700 I had. If macro dynamics are important to you, I would avoid these. It might also not be helping the amount of sub-bass presence this headphone has as I did have to overcompensate to get rumble and better extension.


Detail wise, I feel these are just about right for their price point. At the time of writing this review, they are on sale for $390 on Drop, although already out of stock for anyone with 120V. I find them a decent offering in this aspect. Just comparing it to my HD 650 which is about $220 if you Drops version, it is getting out resolved by the 95x. Although it is not a groundbreaking amount of more detail you are getting with the 95x. It sounds about right for the price difference.


Separation wise, it is pretty good as the HD 650 seems to be suffering in this regard in comparison. The 95x easily comes out on top in terms of separating instruments and making it seem less congested in busier songs. From memory, I believe the amount of separation is closer to an Elex but I am not completely sure as it has been a year since I listened to those.

Soundstage and imaging

I would say the soundstage is a bit above average, being bigger than the HD 650 easily, and being a bit bigger than the elex was. Imaging wise, I feel it is pretty well on the left right and back sides, but the front image is a bit hazy feeling. But it is somewhat there just not as defined as it could be.


Sennheiser HD 650:

Both seem to share a bit more of a warmer signature, with the Koss seeming to have a bit more energy in the upper treble and less energy in the bass. I can see the 95x being an upgrade in terms of separation, soundstage, imaging, and detail retrieval. Although I believe the 650 still does macro dynamics better. The Koss is more suited to some one not really relying on dynamics or intense amounts of bass. The 650 is a good bit nicer with its timbre though.

Focal Elex:

Memory is a bit hazy on this one. But I do remember the macro dynamics being exceedingly well for the price and blowing out the 95x in this aspect. Detail retrieval wise, I feel the elex might be a tinge better but it is not a groundbreaking amount, mostly just in the amount of clarity the Elex has over the 95x. Soundstage wise the 95x is better, and comfort in my opinion is better on the Koss as well. I do find the elex to be a bit more offensive in the upper treble though and shout over the Koss though.

Would I buy it?

I think the Koss ESP 95x is great system for anyone interested in getting in the electrostat sphere. For the price I would easily take this over the L300 + 252s but if you do value detail and only that, I would consider the L300 instead. The 95x is so much nicer tuned than the lambdas Stax has currently on offer, that makes ms turn to the Koss instead. Stax’s lambda series can be offensive in the shout and the treble can be leaning towards the bright side.
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Makiah S
Makiah S
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This review would be so different and swing more in 95X favor.
If it was pair up with a decent energizer using a Stax adaptor.
The stock one is an absolute shocker, even much worst than the one that came with the HE60.
Makiah S
Makiah S
I disagree actually, I've got a Mjolnir Modded SRM 007tA from @spritzer it does make a difference however I feel swapping the original stock pads for Vesper pads makes more of an impact... so spending $80 goes a lot longer than $2,000 :/

Maybe I'd enjoy a better solid state amp with 95X but the tube one I have does have slightly better bass energy and timbre.Still tho I usually swap between my HD 600 and 95X depending on what I'm watching/listening to
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Headphoneus Supremus
Pros: Price
Fast music response
Levels of detail
Cons: Creaky plastic is distracting, and also leaves a nagging doubt in ones mind, that they will break each time that you take them off your head.
I had been thinking about trying electrostatic headphones for a while, so when I spotted these on Drops european warehouse closing down sale, i jumped at the chance.
I found them very enjoyable with acoustic jazz - delivering the same levels of detail that I experience with Aeon Flow Closed, but adding a faster response plus a feeling of more air or space around some acoustic instruments.
For sources, I used a Chord Mojo and Hugo2, and both provide the levels of music detail, that the Koss can then well deliver.
I found the split volume control irritating at first, but I got round the problem by setting the controls for a comfortable volume (and never touching them again), and relying on the dac volume controls for fine tuning.
My main irritation is the creaky plastic. I realise that the original Koss were intended to be portable, and the plastic helps to keep everything low weight. However the plastic creaks too much, to feel like a premium piece of kit, and you have the continual fear that sooner or later the plastic will break. I deducted half a mark for this.
I didn't experiment with alternative power supplies, but I will now consider the option.
Overall if you enjoy acoustic jazz, then a simple system using a Chord Mojo, plus the Koss, is going to be hard to beat in terms of value for money.
Pros: Detailed and non-fatiguing sound that is especially great with vocals and instruments. Good for quiet to moderate listening volumes. Sound can be improved with a better power supply. Light-weight. Front 3.5mm input.
Cons: Cheap, creaky plastic and earpads that are noisy when rubbing. Split volume control difficult to turn without losing balance. Vibrates with low bass. The sound isn't so "punchy" and gets shouty at higher volumes.

The Koss ESP950, as they are originally known debuted in 1990, around the time I got my first pair of headphones. I wish I had known about them then, though they would have cost a fortune back in Australia at that time. A pair of Sennheiser HD600 or HD650 cost around $8-900!

Not having changed at all since then, they look like a relic of the 80s, from the cheap, creaky plastic to the internals. Unusually, they come disassembled, with the driver assemblies detached from the head pad. Given that the original set comes with a battery pack, this old attempt at portability makes sense.

Maybe initially confusing is that high-voltage electrostatic headphone systems ("'stats" for short) can be powered off a simple battery. The hint is in the word "electrostatic". Like static electricity, which is high voltage with almost no current, electrostatic headphones run off the same kind of power hundreds of volts, but with almost no current.

Drop Koss ESP95X D75_9557.jpg

Unfortunately, that means that they cannot plug into a regular headphone amp, instead requiring a driver box, for which Koss provides a surprisingly light-weight unit. As well as RCA inputs on the back, a 3.5mm input is included on the front for portable use. The Drop version of the unit doesn't include the battery pack, nor cables. The ESP950 normally sells for $999 ($899 on Amazon, last I checked), and occasionally $699 on sale. Drop is offering it for $450 in this simplified configuration.

Not having magnets, electrostatic headphones are very light, and these sit gently on your head, and are joined in some plastic creaking by the noise of the material on the cheap ear pads rubbing up against your face.

Drop Koss ESP95X D75_9558.jpg

They were a very welcome relief from the somewhat heavy Final D8000 Pro which are in for review. Set-up is straight-forward. Plug in the wall-wart, a DAC of choice, and the earspeakers (as stats are traditionally referred) with their proprietary connector. At power on, the light indicates green if the power is good, red if not.

The volume adjustment, like Stax driver units, is split between left and right. Being small, it is hard to turn them equally together (I wish they had taken a leaf from Stax or Luxman, both who know how to do split volume controls that turned together unless deliberately adjusted separately). I am tempted to put a couple of drops of super-glue or tape on them to make them turn together.

Putting aside the creakiness, the sound is what makes these so nice to listen with. They are tuned somewhat speaker-flat, which is a bit more mid-forward than what I would call listening neutral than comparably-priced headphones like the Sundaras are tuned. Whereas most headphones are more punchy, the Koss are more airy, with music floating out to you. They extend well in both directions, but low bass doesn t have kick, and turning up the volume makes them more shouty around the mid-range.

Where they may not be good for thump, their strengths are in their lack of fatigue, one which comes without rolling off the treble or being soft. Vocals and instruments come through with a competent clarity which is very enjoyable, and there is a sufficient amount of bass that, combined with the speed of the diaphragm, makes fast-paced music a fantastic listen.

Drop Koss ESP95X D75_9558.jpg

In that vein, the classic question is, Have you been Shpongled? as the very rapid beats of this famous psychedelic music are a great match with stats, the Koss being no exception.

Compared to the Drop Sennheiser HD6XX, the Koss unit sounds far more open, the HD6XX seemingly much more closed-in, even with a good amp such as the THX AAA 789. Closer competition was provided by HiFiMan s Sundaras, which came across as slightly v-shaped in sound, while offering much the same level of performance, or more with a good amp (and thus significantly greater outlay).

However, the Koss driver unit was readily improved if I substituted the included wall-wart with a linear power supply. Adjusting a spare one to 9V output, a slight muddiness that pervaded the sound went away, and the bass became tighter. While not giving it slam, it pushed the Koss unit into territory that if it weren't for the ear pads, I would seriously consider them for daily use.

Considering them as a serious use contender, I ran them with a variety of DACs from Schiit, Audio-gd and Topping. I could not find fault with using any DACs I had on hand, I would say that the Yggdrasil is overkill, as while the Koss were quite detailed, even using the linear power supply, they didn't bring out the finest nuances of the music as my high-end headphones do.

When I want a quiet, relaxing listen, and can overlook the cheap plastic, the Koss ESP/95X is a good-value system, allowing a delicate precision at quieter volumes. Especially for the quieter listener, this is a very good unit that isn't source-fussy.

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No it won't I'm using a 3A custom adaptor and it works fine.
Erfan Elahi
Erfan Elahi
I see people says stax earspeakers also made of cheap plastic. Is electrostatic technology works better on light plastic?
Nope it to cut cost imo. The higher end Stax aren't made of cheap plastic.