Massdrop X KOSS ESP/95X Electrostatic Headphone Review

[milosz]

I have a pair of these Koss electrostats. They're pretty good in my opinion, though not SOTA.

I've had Audeze planar phones too, which I sold after a while. The Audeze had more solid bass, but sounded dull in the mids and highs in my opinion.

 

[Soandso]

... I'd like to be able to correct the response acoustically as there are electrostatic heapdhones with better response. I have no idea what kind of damping needs to be done and am not keen to open them up really.

There are those with the opinion that electrostatic headphones' actually sound better with minimal damping. Here's a screen shot from a different forum's 2020 on-line Koss-950 thread with an electrostatic headphone restorer's opinion about the un-desirable stock damping and then immediately below the positive feedback of one who took that advice. (I never owned this headphone.)

 

[donjoe0]

Mine have had a more noticeably 3-lobed stage since the original shallow wrinkly vinyl earpads broke down and I replaced them with deeper solid sheepskins. I tamed the inner wall reflections somewhat by applying some fuzzy fabric tape (the cable organizer stuff), but that only works through absorption, so it dulls out the treble while not quite restoring the stage I was used to. I plan to take that tape off and apply something to work more like a diffuser, I think that should fix the reflections without dulling anything.

Front and back damping I would not think to touch, as those contribute to dust protection, I imagine.

Wrt. my earlier interventions about how long they need to stay plugged in, further experience has shown me simply staying plugged in doing nothing is no help to their sound, it was all based on playing music through them. So anytime they've been unpowered they need a good 7h of music playback until they sound their best, otherwise they're no better than an HE-400i. I do keep them powered as long as possible so I don't have to do the 7h thing too often, and I think that's also reducing the incidence of any static squealing or crackling noises to almost zero.

 

[isostasy]

I have a pair of these Koss electrostats. They're pretty good in my opinion, though not SOTA.

I've had Audeze planar phones too, which I sold after a while. The Audeze had more solid bass, but sounded dull in the mids and highs in my opinion.

Even with EQ?

There are those with the opinion that electrostatic headphones' actually sound better with minimal damping. Here's a screen shot from a different forum's 2020 on-line Koss-950 thread with an electrostatic headphone restorer's opinion about the un-desirable stock damping and then immediately below the positive feedback of one who took that advice. (I never owned this headphone.)
View attachment 446836
View attachment 446837

Thanks, I'm not sure what they mean as there is no "damping inside the earpads". Someone on SBAF has pictures, in the first they've removed the foam dust protector but this is very thin and open, moreso than what Sennheiser use for the HD6xx series I think. So you can see behind this there is no damping. That person actually adds more material (foam) onto the plastic baffle and more confidently blocks the the slots in the baffle. It looks fairly simple and non-destructive so I might try it though I can't see how it would change the sound.

Mine have had a more noticeably 3-lobed stage since the original shallow wrinkly vinyl earpads broke down and I replaced them with deeper solid sheepskins. I tamed the inner wall reflections somewhat by applying some fuzzy fabric tape (the cable organizer stuff), but that only works through absorption, so it dulls out the treble while not quite restoring the stage I was used to. I plan to take that tape off and apply something to work more like a diffuser, I think that should fix the reflections without dulling anything.

Front and back damping I would not think to touch, as those contribute to dust protection, I imagine.

Wrt. my earlier interventions about how long they need to stay plugged in, further experience has shown me simply staying plugged in doing nothing is no help to their sound, it was all based on playing music through them. So anytime they've been unpowered they need a good 7h of music playback until they sound their best, otherwise they're no better than an HE-400i. I do keep them powered as long as possible so I don't have to do the 7h thing too often, and I think that's also reducing the incidence of any static squealing or crackling noises to almost zero.

Interesting that the deeper pads worsened it for you. Maybe try the solid foam under one side of the inner pad and gently bending the metal headband arms in to get more of an angle.

I don't know enough about them or the technology to comment on the static squealing. My experience is simply tapping on the cup makes it go away. I'd be surprised if leaving them on playing music for that long is necessary.

 

[Soandso]

About "dust" : the actual dust barrier on electrostatics is the transparent plastic layer; as seen in member iso's linked photo.

Overly damped there is potential for mid-range frequency effects. If you hear frequency alteration depending on how the ear cups are positioned while wearing the headphones that would be an indication the damping can be reduced.

On the Koss-950s leaving them with just a little damping is suitable for controlling resonances.

For damping I use melamine which is an open cell foam material the sound waves penetrate. Inside that matrix the sonic energy becomes a low heat and reflections are reduced. Melamine resin, used to make the foam, has a high % of nitrogen which can create fire resistant foam good up to about 350*Fahrenheit ( nor does it melt or drip in open flames).

On e-stats I have used the pictured melamine (seen below set on a brown table edge next to a sheet of photo-copier paper for thickness comparison and lastly seen from above) bought in a USA supermarket package of "Mr.Clean Magic Eraser Power Wipes" 16 hand-sized sheets. Each sheet is only 0.1cm (0.03 inch) thick; can be stacked and easily cut to shapes. The surface texture of these sheet's may, or may not, be the same as industrial quality rated melamine.

 

[Soandso]

Belatedly addressing the question of above post #144 as to what damping "inside the ear pads" means. The quoted e-stat repairer is not a native English speaker. From their additional reference to damping "on the back of the drivers" I presume "inside" meant the foam damping beyond the bottom surface of the ear pads looking inward and directly underneath the hard molded plastic baffle.

If we are talking about an older set it is possible whatever original foam damping has deteriorated - not necessarily crumbling and shedding particles, maybe just losing foam cells' shape broken down with some compacted areas. So should this discussed set be old it might be worthwhile replacing the visibly altered foam with a bit of melamine sheets. This stuff is easy to position for minimal damping, add to in order to incrementally experience greater damping or then remove excess layers.

 

[Svperstar]

I have had these for a few months, wanting to try the electrostatic / large diaphragm experience for cheap.

I use them with Vesper Audio pads which, although not fixing the poor frequency response, do make them much more comfortable and ensure better seal for bass. I put a strip of foam in them to angle them a little and have gently bent the metal headband connectors in a bit as they are were loose on my small head.

Here's my EQ:

Filter 1: ON LSC Fc 40 Hz Gain 6.0 dB Q 0.800
Filter 2: ON PK Fc 1000 Hz Gain -4.0 dB Q 1.000
Filter 3: OFF PK Fc 2000 Hz Gain 2.0 dB Q 0.500
Filter 4: ON PK Fc 3300 Hz Gain 2.0 dB Q 2.000
Filter 5: ON PK Fc 5600 Hz Gain -3.0 dB Q 4.000

If you have the velour pads just turn Filter 3 on as that approximates the difference. The low shelf is obviously to taste, sometimes I prefer 9dB at 0.6 Q for a warmer sound. Filter 5 is very subtle and not necessary unless that region bothers you, which I've found it often does me.

I do think they sound very good with EQ. They sound different to my HD6XX even though the EQ'd response is very similar - in particular they sound brighter in a way that belies the measurements and I suspect is due to the soundwave created by the large diaphragm interacting with my ear to create a different perception of treble than what is seen on a dummy head. I've noticed some spatial qualities, though not really "soundstage" which is a concept I struggle with. More like separation and openness though I realise these are unhelpful and overused terms. I get a bit more of a feeling of bass around my ears as well in contrast to the HD6XX and IEMs where the bass feels narrowly transmitted into your ear canal.

I suspect the electrostatic technology has nothing to do with it and that any perceived benefits are due to having large, open cups and diaphragms. This makes me think that planar magnetic headphones with similarly, or even larger, drivers would have the same benefits - and without the need for an energiser and the occasional appearance of an annoying whine. So now I'm tempted by those nice big (and much more expensive) Audezes.

I have flat-plate coupler measurements which I can share though they're of limited use; the cups are so large I have to take a lot of measurements and average as the response changes depending on position, so it's hard to know exactly how it relates to on-head response.

I'd like to be able to correct the response acoustically as there are electrostatic heapdhones with better response. I have no idea what kind of damping needs to be done and am not keen to open them up really.

Did you listen to the 95X out of the Koss energizer box or a Stax energizer?

 

[isostasy]

Belatedly addressing the question of above post #144 as to what damping "inside the ear pads" means. The quoted e-stat repairer is not a native English speaker. From their additional reference to damping "on the back of the drivers" I presume "inside" meant the foam damping beyond the bottom surface of the ear pads looking inward and directly underneath the hard molded plastic baffle.

If we are talking about an older set it is possible whatever original foam damping has deteriorated - not necessarily crumbling and shedding particles, maybe just losing foam cells' shape broken down with some compacted areas. So should this discussed set be old it might be worthwhile replacing the visibly altered foam with a bit of melamine sheets. This stuff is easy to position for minimal damping, add to in order to incrementally experience greater damping or then remove excess layers.

Ah that makes sense, mine are quite new I think so don't see any foam deteriorating. Where do you put your melamine sheets?

Did you listen to the 95X out of the Koss energizer box or a Stax energizer?

Just the stock Koss energizer which came with the headphones

 

[donjoe0]

Interesting that the deeper pads worsened it for you. Maybe try the solid foam under one side of the inner pad and gently bending the metal headband arms in to get more of an angle.

I was doing that with the shallower ones, but I no longer have the kinds of problems I expect to solve by making the pads even deeper and improving the seal even more. The staging problems I assume are from pad wall reflections. I need to tweak the pad wall surface structure.

I don't know enough about them or the technology to comment on the static squealing. My experience is simply tapping on the cup makes it go away.

Same, but it also happens so rarely I have time to forget they even have such a problem. It's way less frequent than when they were a new toy and I was experimenting with how long they need to be powered and/or playing, A/B-ing vs. planars etc.

I'd be surprised if leaving them on playing music for that long is necessary.

I've tried it enough times that it's no longer a surprise to me. Freshly powered they have nothing on my HE-400i except a taller stage from the oval cups. With 7-8h of music the bass extends lower and gets decent impact, and the highs get more coherent and present more detail. That's the only condition where I feel I'm getting my money's worth out of them, otherwise there would be no point in keeping them when I already have the 400i.

I see people are reporting similar requirements with older round-driver Stax, which "get good" in half an hour to 1-2 hours. I have to assume it's something to do with differences in membrane manufacturing quality and differences in membrane size, both determining how easily you can get a uniform charge spread and the consequent planar-as-it-gets movement.

 

[Soandso]

Ah that makes sense, mine are quite new I think so don't see any foam deteriorating. Where do you put your melamine sheets?

On the ~50 year old e-stats I recently restored it was obvious they needed to get rid of all the original foam. So right underneath the driver assembly slid a few cut down melamine sheets one atop the other and against the inner surface of the ear cup rear sized in a single layer sheet. No gluing down was need. (I didn't put any over the driver dust cover on the side facing the ears, but the re-cycled replacement ear pads I used themselves have a light woven fabric that covers that baffle opening toward the ear.)

 

[Svperstar]

Just the stock Koss energizer which came with the headphones

The 95X was my introduction to estats, I decided to go "all in" on estats in late 2023. The entry level or baseline Stax T1S was my first Stax amp. I got a used adapter cable that lets you use the 95X with any Stax compatible amp.

I think I audibly gasped the first time I listened to the 95X out of a Stax amp. A good amp radically transforms the performance of the 95X. The energizer it comes with is the limiting factor of the headphones, not anything in the driver.

 

[donjoe0]

I think I audibly gasped the first time I listened to the 95X out of a Stax amp. A good amp radically transforms the performance of the 95X. The energizer it comes with is the limiting factor of the headphones, not anything in the driver.

Any guess as to how it would functionally, electrically, produce such a difference, as long as the voltage specs are the same? Because there's this power supply builder person on (Mass)Drop - nickname "nottagorilla" - who is adamant that there is zero wrong with the E/90x energizer OR its power brick, and that that is enough to make the ESPs sound better than whatever Abyss 1266, Audeze or other top-tier planar you'd care to compare them to, and gets them already up to par with Stax.

 

[Soandso]

Any guess as to how it would functionally, electrically, produce such a difference, as long as the voltage specs are the same? … zero wrong with the E/90x energizer OR its power brick …

My best guess: the Koss portable unit plugged into a wall socket uses 9 watts in a design requiring high rail voltage. The e-stat bias uses 600 volts with a resistor feeding into a capacitor (at the amp's bias output the voltage measurement will be much lower). Thus the reported sound limitation is not in voltage but the small transformer size; it's weight is light (portable) due to limited wire windings. As I understand the relevant nuance here it is a transformer's winding ratio which can influence the quality we get to hear in the music's high frequencies - the voltage supplies quantity, so the high frequencies are none-the-less there for the Koss. Hence bloggers report their Koss headphones sound "better" or "open-up" when the audio channels are driven by non-Koss energizers/amps even with some discrepancy in voltage. [Again: I have no experience with Koss-950.]

 

[Svperstar]

Any guess as to how it would functionally, electrically, produce such a difference, as long as the voltage specs are the same? Because there's this power supply builder person on (Mass)Drop - nickname "nottagorilla" - who is adamant that there is zero wrong with the E/90x energizer OR its power brick, and that that is enough to make the ESPs sound better than whatever Abyss 1266, Audeze or other top-tier planar you'd care to compare them to, and gets them already up to par with Stax.

I'm not an EE, I could email the builder of my latest estat amp and ask. I understand it is very weak and doesn't provide much current. If you plug the Koss into a Stax amp the bass is what immediately jumps out at you. As Amir's measurements show the 95X is bass deficienct with a pronounced dip. This is the energizer not the headphones

 

[isostasy]

I was doing that with the shallower ones, but I no longer have the kinds of problems I expect to solve by making the pads even deeper and improving the seal even more. The staging problems I assume are from pad wall reflections. I need to tweak the pad wall surface structure.


Same, but it also happens so rarely I have time to forget they even have such a problem. It's way less frequent than when they were a new toy and I was experimenting with how long they need to be powered and/or playing, A/B-ing vs. planars etc.


I've tried it enough times that it's no longer a surprise to me. Freshly powered they have nothing on my HE-400i except a taller stage from the oval cups. With 7-8h of music the bass extends lower and gets decent impact, and the highs get more coherent and present more detail. That's the only condition where I feel I'm getting my money's worth out of them, otherwise there would be no point in keeping them when I already have the 400i.

I see people are reporting similar requirements with older round-driver Stax, which "get good" in half an hour to 1-2 hours. I have to assume it's something to do with differences in membrane manufacturing quality and differences in membrane size, both determining how easily you can get a uniform charge spread and the consequent planar-as-it-gets movement.

I might try taking measurements straight after powering up and after a few hours to see if this is measurable. I haven't used them long enough to experience anything similar. The frequency response is so different to the HE-400i though.

 

[isostasy]

On the ~50 year old e-stats I recently restored it was obvious they needed to get rid of all the original foam. So right underneath the driver assembly slid a few cut down melamine sheets one atop the other and against the inner surface of the ear cup rear sized in a single layer sheet. No gluing down was need. (I didn't put any over the driver dust cover on the side facing the ears, but the re-cycled replacement ear pads I used themselves have a light woven fabric that covers that baffle opening toward the ear.)

Interesting I will give this is a go and see if it changes the response. Now you mention it the vesper pads I'm using have a built in fabric dust cover too.

 

[isostasy]

The 95X was my introduction to estats, I decided to go "all in" on estats in late 2023. The entry level or baseline Stax T1S was my first Stax amp. I got a used adapter cable that lets you use the 95X with any Stax compatible amp.

I think I audibly gasped the first time I listened to the 95X out of a Stax amp. A good amp radically transforms the performance of the 95X. The energizer it comes with is the limiting factor of the headphones, not anything in the driver.

My best guess: the Koss portable unit plugged into a wall socket uses 9 watts in a design requiring high rail voltage. The e-stat bias uses 600 volts with a resistor feeding into a capacitor (at the amp's bias output the voltage measurement will be much lower). Thus the reported sound limitation is not in voltage but the small transformer size; it's weight is light (portable) due to limited wire windings. As I understand the relevant nuance here it is a transformer's winding ratio which can influence the quality we get to hear in the music's high frequencies - the voltage supplies quantity, so the high frequencies are none-the-less there for the Koss. Hence bloggers report their Koss headphones sound "better" or "open-up" when the audio channels are driven by non-Koss energizers/amps even with some discrepancy in voltage. [Again: I have no experience with Koss-950.]

I'm not an EE, I could email the builder of my latest estat amp and ask. I understand it is very weak and doesn't provide much current. If you plug the Koss into a Stax amp the bass is what immediately jumps out at you. As Amir's measurements show the 95X is bass deficienct with a pronounced dip. This is the energizer not the headphones

Can you tell a difference level-matched though? I'm with others in that I can't see how the Stax amp would make a difference unless it is getting you to a louder volume you want, which seems plausible from amir's electrostatic amp comparison where he says "we run out juice at nearly 10% of what the Stax amps can produce".

I don't see anything in the measurements showing a dip resulting from the energizer. If anything it shows a (slight) level dependent boost.

I don't think any of this matters without using EQ though: the stock response is so poor you really need EQ to fix the mid-range. I wouldn't listen to these full stop without the EQ I posted above.

 

[Soandso]

I understand it is very weak and doesn't provide much current. If you plug the Koss into a Stax amp the bass is what immediately jumps out at you. As Amir's measurements show the 95X is bass deficienct with a pronounced dip. This is the energizer not the headphones

This brings up some measured factors. The stock E-90 Koss amp using 9 Watts provides ~2 mAmps/Volts per audio channel while old Stax amps use about 30 Watts and provide ~11 mAmps/Volts per audio channel.

So even though the Koss is set for 600 Volts bias while Stax "pro" bias is set for 580 Volts and the Koss amp can swing more peak to peak voltage it's current constancy is lower. The portable size Koss amp can't accommodate a proper heat sink and so it's design incorporates a high rated resistor to prevent the plastic from becoming heat damaged.

My surmise is that compared to a Stax amp design the Koss amp incurs an earlier and steeper drop off of frequencies starting about 1,200 Hz and becoming noticeable around 2,000 Hz. While the lower Koss amp's current in context of it's small transformer adds conceivably up to 2.2 milliSeconds of sonic group delay to the over 2,000 Hz frequency roll offs.

Then too the Koss amp being designed for portability running off of D.C. (batteries) when plugged into the wall A.C. adds another factor. The internal amp circuitry for taking A.C. into the required form of D.C. likely adds "noise" which a suitable Stax amp would not.

 

[Svperstar]

Can you tell a difference level-matched though?

Yes. Its not even a contest, as someone said in reply below your question Stax amps provide more current then the Koss box is capable. Custom amps even more so.

I don't have any measurement gear here but I have tried going back and forth between the Koss box and Stax/custom amps and the 95X headset is being held back by its amp.

Maybe an EE can explain in detail why.

This guy on YouTube upgraded to a Stax amp just for his 95X, He mad his own connector. I got the Dan Fong cable for half-price used: