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Massdrop X KOSS ESP/95X Electrostatic Headphone Review

amirm

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#1
This is review and detailed measurements of Drop's X KOSS ESP/95X electrostatic headphone. It is on kind loan from a member and when it was available, cost US $500. Not sure what is different with it from the original KOSS model which I think cost $1000.

Typical of most electrostatic headphones, there is a required amplifier/driver ("energizer"):

MASSDROP X KOSS ESP 95X ELECTROSTATIC headphone stereo review.jpg


The headband separates from the earphones using a clever and simple button on each side. The rest is not so impressive as the plastic is what $10 toys would be made out of. Same applies to the amplifier which looks metal in the picture, but is very cheaply made plastic. The plastic has one advantage: the headphones are super light. Wearing them was comfortable for the 2 hours or so that I used them for testing.

The headband friction fit is too loose so the position of the headphones does not stay the same. Pull them on and off and they change.

The retainers on each side of the earphones creeks as you move around.

The most major flaw is the volume control. They copied the one from Stax where you have the left and right volume on the same shaft. On Stax, you adjust the two but then when you turn the very large knob, both channels adjust at the same time. Not so here. It is darn near impossibly to adjust the volume and not have one channel change more than the other. It was so frustrating that that I gave up on using it and set it to near max and used my DAC's volume control.

Massdrop X KOSS ESP/95X Measurements
I measured ESP/95X on GRAS 45CA standardized headphone measurement gear which is (still) on loan from the company. The drive and analysis was the Audio Precision APx555. Let's start with our new dashboard:

MASSDROP X KOSS ESP 95X ELECTROSTATIC SYSTEM stereo Measurements.png


Distortion is quite low for low frequency source tone of 40 Hz (peak amplitude in sampling of music). We can see second harmonic at 80 Hz to the tune of -65 dB which is quite good.

Most important measurement though is frequency response:

MASSDROP X KOSS ESP 95X ELECTROSTATIC SYSTEM Frequency Response Measurements.png


The dashed blue line is most preferred frequency response for a headphone. Between 200 and 3 kHz, we have decent agreement. Below that we have significant deficiency which is the case with many headphones. We do have drooping in lower treble as indicated by the cursor lines near 5 kHz. There is also some extra energy around 1 kHz. Lack of bass and highs would indicate a sound that would be rather flat and unexciting.

While I have become comfortable with the above comparison of measurement versus expected, some people may want to see the two substracted from each other and look at the deviation. A flat line here then indicates 100% compliance with the preference curve:

MASSDROP X KOSS ESP 95X ELECTROSTATIC SYSTEM Compensated Frequency Response Measurements.png


This looks a lot worse than many other measurements out there. The reason is that I use 20 dB span and others use many multiples of this. Increase the range vertically enough and you can make any frequency response look flat!

Anyway, we see the shortfall in bass from 200 Hz down. There is that strange shelving which may be some kind of electronic filtering in the amplifier.

As usual, ignore stuff at or above 10 kHz.

Somehow I lost my IMD vs level test from the last review. :( Until I recreate it, let me treat you to other distortion graphs:

MASSDROP X KOSS ESP 95X ELECTROSTATIC SYSTEM Frequency THD Distortion Response Measurements.png


For some reason this AP graph only shows second and third harmonic. Note that this is pure THD and has no noise in it.

Comparison to Stax SR-303 Headphones
I thought it would be good to perform a quick comparison to one of my Stax headphones, the SR-303 driven by their lower end SR-313 amplifier:

Stax SR-303 Eelectrostatic Headphone Frequency Response Measurements.png


This response has a much better adherence to our preference curve. We have matching bass down to 50 Hz compared to 200 Hz in ESP/95X. And then slopes down gradually, kind of like a speaker would. This looks like some kind of high pass filter.

Massdrop X KOSS ESP/95X Listening Tests
Out of the box the sound was decent. I think having that first peak in the 3 kHz help to not have a hollow sound. That said, lack of bass is obvious, and there is little sparkle. I heard no "speed" people talk about. Once again I think people take the lack of bass and equate that with 'speed." The large earphones do provide a taller presentation which as a fun exercise, you can adjust up and down as you move the cups.

I decided to use EQ to improve things and this was more time consuming than I expected. Here is where I landed:

MASSDROP X KOSS ESP 95X ELECTROSTATIC headphone equalization EQ.png


I had to build a custom bass boost for it as you see above. It responded very well to this.

There was some extra energy around 1 kHz. I went back and forth on this a fair bit but at the end, I decided to take it out using that teal Band 1 filter.

This last bit was the most complicated. I tried to boost what was missing around 5 kHz, but not let the overshoot at 6 kHz make it too bright. I think a more proper automatic filter generation may work better here than my eyeballing it.

When it was all said and done, the ESP 95/X went from rather unexciting and dull to a "hifi speaker." We now had bass, more highs and less midrange emphasis. Indeed I enjoyed it for a couple of hours listening to a lot of music.

Then out of the corner of my eye I saw my Stax SR-303 and decided to listen to that. The tonality of the Stax out of the box was way more pleasant than the ESP/95X. The Stax material was also in a completely different class. This prompted me to then measure the Stax as you saw in the previous section, confirming what I was hearing.

There was a difference though: the ESP/95X could barely get loud enough for my music selection. The Stax misses that mark. Turn it up beyond a certain spot and the drivers start to crackle.

Conclusions
I don't know why people are so fascinated with how some speaker/headphone is made. What matters are the results. If full frequency response is not delivered faithfully, I don't care if you bring a live orchestra to my room. I won't like it. We have that problem here to some extent. The frequency response deficiencies are there and are significant but are not show stoppers. Correction is mandatory unless you want something plain sounding with little dynamics, bass and sparkle in the highs.

The ESP95/X didn't light up any magic for me that people talk about other than what the large size of the driver brings.

If you are itching to hear what electrostatic headphones are about, you can opt opt for these and I won't chase you out of town. Otherwise, I suggest looking for a headphone with better response. So while I can't recommend the Massdrop X KOSS ESP/95X, I am not opposed to them either in a sea of other headphones, many of which are worse than it.

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Degru

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#3
That 303 is not sealed properly. It should extend flat to 20hz and below. Both the 202 and 404 can do so, the 303 definitely should as well as it has a near-identical design.
 
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amirm

amirm

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Thread Starter #5
That 303 is not sealed properly. It should extend flat to 20hz and below. Both the 202 and 404 can do so, the 303 definitely should as well as it has a near-identical design.
It was a quick test. I will play with more placement when I do a review on it.
 

xup

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#6
I think people are fascinated with how certain headphones are made as they can (hypothetically at least) find patterns such as "this and this type of headphones have more bass" etc and they can get a certain feel of the sound without listening or to refer to people. Not saying it is always useful, just my insight.
 
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#7
I used to love my Stax back in the 90s, they did sound very open and detailed, but the bass was just not there.

It looks like these headphones are very similar in sound.
 

Blumlein 88

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#9
I had some of the really old Koss electrostat phones from back in the 1970's. ESP 9's. I owned them in the early 1990's and Koss had checked them out as good as well as replacing the pads and such on them.

I had early Stax Lambda and later Stax electrets both of which I consider better than the old ESP9's. I did get to hear some of the newer Koss briefly once, and they in general sounded like the old ones I had. Not dissimilar to Amir's description here. All this is from old memory in my case.

1603259055396.png
 
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amirm

amirm

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Thread Starter #10

ROOSKIE

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#11
That 303 is not sealed properly. It should extend flat to 20hz and below. Both the 202 and 404 can do so, the 303 definitely should as well as it has a near-identical design.
Howdy do you know are there some measurements published and available that show these responces reaching to 20hrz?
 

Degru

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#12
It was a quick test. I will play with more placement when I do a review on it.
It is possible it may not be able to seal correctly on the measurement rig without some sort of sealant in between (a friend of mine used vaseline); lambda pads are contoured to fit on a human head and it is very common for them to have problems sealing with non-malleable non-human-shaped apparatus. Beware that this completely throws off distortion/IMD measurements as well since the driver resonates like hell and isn't operating within its intended mechanical design. You can see this behavior in your own early measurement of the 007:
1603259119052.png 1603259166635.png 1603259260215.png
In reality the Stax should have easily beat all the rest of the headphones on that IMD and THD test up to its loudness limit if it was properly sealed.
 

Degru

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#14
Howdy do you know are there some measurements published and available that show these responces reaching to 20hrz?
I don't have measurements of 202 and 404 specifically (at least, none that I can post yet without permission) but here are two examples of Lambdas with good and bad seal:
Lambda Pro (from someone I know on Discord):
1603259628252.png

Unknown lambda from SBAF stax thread (this one is not perfectly sealed even on the "good" measurement because it humps and drops at 20hz, but you get the picture):
1603259694905.png

Neither of these are standardized rigs, but the bass behavior should still be relatively accurate and repeatable on any rig with these headphones. Basically all of the lambdas up till the L300-700 and 007mk2 (which are ported) will exhibit this behavior when measured with good vs bad seal onto the rig.

Personally, I have used 202, 404sig, Lambda Signature, and own a 404LE, which all have flawless bass extension to my ears, and will measure with flat bass extension on properly done measurements.

Edit: stax's own measurement from the back of my 404LE manual:
20201020_230513.jpg

Lambda signature manual:
1603260708972.png

You get the picture. No high-pass filters here. You will find many measurements of older Lambdas with a midbass peak and bass rolloff due to bad seal, but these are not representative of how they actually perform, no matter how some may try to convince you otherwise. @amirm take note.
 
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Cahudson42

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#15
Thanks, amir! One more data point - soon we will be looking at a table of dynamics, planars, and electrostatics!

I know, as with electronics and speakers, the HP tests will gradually build...

I do find myself uneasy with the single 40Hz distortion measurement, and liked the new single 'sweep' graph you included.. Will these be at some 'standard' SPL? I seem to have missed it...100? Like dashboard?

I also think some kind of 'pulse response' test(s) particularly at lower and mid fr(s) might be indicative. Damping, overshoot, ringing - whatever the correct term(s) - that indicates inability of the transducer to faithfully follow the incoming pulsed waveform. Any of this should also show up as a form of distortion, and be measureable - I would hope...

EDIT: Some ideas - see @solderdude ,'Impulse Step Response' etc. https://diyaudioheaven.wordpress.com/tutorials/how-to-interpret-graphs/squarewave-and-impulse/

Keep up the great work!
 
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amirm

amirm

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Thread Starter #16
on windows with apo eq (like peace) its done in under 5 min.... but that's somewhat special ...so i should have written instead : " it can be done fast and it is simple( if you use desktop)"
I don't mean activating them. But rather, how close the response already is to the target. Without enough filters on paper you can fit just about any response to the target.
 

pavuol

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#17
husband from living room: "What are you doing there honey?"
wife in kitchen: "I'm cooking some delicious meal from our organic vegetables.. and what are YOU doing there?"
husband: "I'm cooking some usable EQ settings for these weird FR stats.."

[all the above characters are fictitious, any resemblence...]
[if you find this "sexist" just call me that or hit the "dislike" button, whatever ;)]
 

pavuol

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Conclusions
I don't know why people are so fascinated with how some speaker/headphone is made. What matters are the results. If full frequency response is not delivered faithfully, I don't care if you bring a live orchestra to my room.
How about someone sending ORA graphene headphones so we can compare the "old schools" to some breakthrough brandnew technology?
 
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#19
I don't mean activating them. But rather, how close the response already is to the target. Without enough filters on paper you can fit just about any response to the target.
sure ... its not trivial to actually get measurable near any target with eq... "on paper" a lot eq is fine that doesn't translate into real life acoustics .... but in praxis its hard to control the headphones reaction to eq. so its somewhat impressive how near you can get with proper eq and how simple it is to use.
 
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