Massdrop X KOSS ESP/95X Electrostatic Headphone Review

[Blujackaal]

The bass in Stax headphones is almost entirely dependent on seal. Some designs seal better on one's head than on a measurement rig, but others make it impossible to get a good seal, and thus good bass extension.

And still needs a +8db bass boost to sound at least bit above flat. The HD650, ER4SR, etc have more bass without EQ. 3 headphones that use ribbion/planar/Electrostatic all need very heavy EQ in the low end to sound above flat, All for £1900?.

 

[ferrellms]

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"):

View attachment 88822

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:

View attachment 88823

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:

View attachment 88824

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:

View attachment 88825

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:

View attachment 88826

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:

View attachment 88827

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:

View attachment 88829

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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What is with "the most preferred response for headphones" and criticizing headphones for flat frequency response? I want ruler flat response, period. Just because a bunch of people like inaccurate bass response? Who cares? Come on. Accuracy is paramount! What people prefer is irrelevant. This reminds me on another Tooleism - that early speaker room reflection is good because people prefer it because it enhances "space". The fact that boosted bass and early reflections color the sound is fine for some, whatever floats your boat. Give me the most accurate representation of the recording please, not what people "prefer". I can EQ it myself, or build in some switchable optional EQ if you want.

 

[sarumbear]

Well, they are the exact same headphones that they were selling some 30 years ago, the Koss ESP/950.

I meant the PRO4, introduced in 1962. ESP/950 was introduced in 1990. I was responding the fact that Koss had not remedied the creaky sound for 60 years till now, even though they have obviously been developing other models.

 

[The Jniac]

What is with "the most preferred response for headphones" and criticizing headphones for flat frequency response? I want ruler flat response, period.

A headphone with a ruler-flat response would sound terrible. If you measure the response at the eardrum of a pair of loudspeakers that measure as perfectly flat at the listening position, you will get a response that is fairly similar to the Harman target, albeit with little to no bass boost. If you want a pair of headphones that sound the same as a pair of speakers that are perfectly flat at the listening position, you will want their raw FR to look essentially identical to that of the Etymotic ER-4SR, possibly with a little more bass since plenty of people found the bass in them to be lacking and I cannot find enough information to determine whether Etymotic messed up somewhere, the people complaining are used to more bass than what is neutral, or if the problem is related to variation in individual physiology when headphones are typically designed for an average person. That last point is also very important and seriously problematic for headphones: due to variations in physiology, what my eardrum receives from a pair of perfectly flat speakers may be quite different to what yours does, and both of us may differ significantly from the average. As such, you, me, and Average Joe/ Average Jane could all listen to the exact same headphone, and yet hear markedly different sounds.

 

[manishex]

How would the Etymotic ER-4XR perform then since it's a sub bass boosted version of the ER-4SR?

The LCD4 gives huge rumbling sub bass that everyone says is intense, powerful and controlled yet the harman target would tell you it needs a 6db boost

 

[ROOSKIE]

What is with "the most preferred response for headphones" and criticizing headphones for flat frequency response? I want ruler flat response, period. Just because a bunch of people like inaccurate bass response? Who cares? Come on. Accuracy is paramount! What people prefer is irrelevant. This reminds me on another Tooleism - that early speaker room reflection is good because people prefer it because it enhances "space". The fact that boosted bass and early reflections color the sound is fine for some, whatever floats your boat. Give me the most accurate representation of the recording please, not what people "prefer". I can EQ it myself, or build in some switchable optional EQ if you want.

You are in a room. It might be a large living room or a tiny "ear" room formed by the earcups or what have you. You must use the room as part of the system - there is ZERO way to remove it and it's effects so the compromise is to realize that and discover what works well. I assure you there are zero recording studios and studio monitor set-ups where albums are mastered that do not affect the results.
Accuracy is not a fixed number in hifi or vary many things in general but rather a probability it will be perceived as such.
The only way to hear what the recording engineers heard was to go sit with them in their studio an use their ears. - even then they are mastering for solid playback on many various devices, there is usually no one gold standard but a look at how the recording comes across in general on many speakers, headphones and other playback devices.
Engineers who use one playback device to master are fooling themselves. Some engineers will use dozens of systems to come up with a final master that is a compromise on 'accuracy" due the fact that all the systems will likely sound different and thus present accuracy differently.

 

[Degru]

And still needs a +8db bass boost to sound at least bit above flat. The HD650, ER4SR, etc have more bass without EQ. 3 headphones that use ribbion/planar/Electrostatic all need very heavy EQ in the low end to sound above flat, All for £1900?.

er4sr also has flat bass? Just like planars and good estats? I'm not sure how it has "more without EQ". And no, *good* planars and estats running off proper source gear do not need very heavy EQ to have good bass. Bass quality depends on more than just FR. Just look at the Campfire Orion. That thing has flat bass on measurements, but sounds limp and rolled off down there when you listen to it yourself. Then you look at an Audeze which also has flat bass and relatively recessed high end, and it sounds completely different. I highly encourage you to actually listen to, say, an LCD2C and then tell me how it absolutely *needs* +8db boost.

One thing people always miss about the harman target is the bass curve is not intended to be a rule. They found different people preferred different quantities of bass, and trained listeners tended to prefer closer to flat. The "official" level in the harman curve is basically an average of all of those. The upper treble is also intentionally heavily rolled off/not really talked about because headphones and headphone measurements vary so wildly in that region it would be impossible to accurately make a target curve for it.

 

[Degru]

How would the Etymotic ER-4XR perform then since it's a sub bass boosted version of the ER-4SR?

The LCD4 gives huge rumbling sub bass that everyone says is intense, powerful and controlled yet the harman target would tell you it needs a 6db boost

ER4XR has a warmer tuning but worse quality and distortion overall. They used a vented BA driver to achieve the bass elevation and it just sounds worse because of it, since the tiny driver can't really keep up. Certainly no bass monster by any means. This is extremely apparent if you try to apply a harman EQ (such as Oratory's) to an er4s; it transforms from an excellent neutral iem to a horrendous boomy mess that sounds like something you get for $5 at the convenience store. If you want a bass boosted ety, get the er2xr because its dynamic driver is far more capable in that region.

Audeze LCD headphones tend to sound bassy even though they have flat bass because the upper mids and lower treble are significantly recessed on them. Everything is relative. The "huge rumbling" quality is simply because it's a huge planar driver with extremely good extension and low distortion that is very capable of producing good bass.

 

[Blujackaal]

A headphone with a ruler-flat response would sound terrible. If you measure the response at the eardrum of a pair of loudspeakers that measure as perfectly flat at the listening position, you will get a response that is fairly similar to the Harman target, albeit with little to no bass boost. If you want a pair of headphones that sound the same as a pair of speakers that are perfectly flat at the listening position, you will want their raw FR to look essentially identical to that of the Etymotic ER-4SR, possibly with a little more bass since plenty of people found the bass in them to be lacking and I cannot find enough information to determine whether Etymotic messed up somewhere, the people complaining are used to more bass than what is neutral, or if the problem is related to variation in individual physiology when headphones are typically designed for an average person. That last point is also very important and seriously problematic for headphones: due to variations in physiology, what my eardrum receives from a pair of perfectly flat speakers may be quite different to what yours does, and both of us may differ significantly from the average. As such, you, me, and Average Joe/ Average Jane could all listen to the exact same headphone, and yet hear markedly different sounds.

I'd say it that people want more bass that either from what music they enjoy or just taste. The ER4XR sounds cleaner than the ER2XR imo, Since i just EQ mine to +3db with 100Hz low shelf without losing clarity. But for neutral the ER4SR's bass is more than enough if you get used to it which is why i don't get the "Avoid the ER4SR" rants i see everywhere?.

 

[SpaceMonkey]

I tend to think that bass boost is used to compensate for lack of reverberation in headphones. Personally I am fine with flat bass as it has little to no bleed into midrange. ETY ER4S/PT forever!

 

[Blujackaal]

It can help but i find harman/ER4XR bass boost too much, The ER4SR/ER4PT being flat imo lets the mids/treble shine & is the right amount. It why i the 4SR is my IEM endgame. I'm watching a Among us stream I'm getting sub bass punch without it sound bloated/fat. Also doing a +2db 40Hz low shelf can fix roll off there.

 

[xykreinov]

He has 8 filters. I wouldn't call that easy.

Really?? Wow, I must be really patient if even the great Amir wouldn't want to mess with 8 filters. Or, just not as busy reviewing equipment

 

[xykreinov]

I tend to think that bass boost is used to compensate for lack of reverberation in headphones. Personally I am fine with flat bass as it has little to no bleed into midrange. ETY ER4S/PT forever!

Yeah, I'm a flat bass kind of guy myself as well. I actually have DT770s I purposefully force a flat bass response out of, despite how much of an especially good job they do with handling bass.
But, it's made very clear (I can't remember by who- Sean Olive?) that the bass portion of the Harman target is the most subjective part. Preferences varied the most for it than any other range of frequencies.
For me, it's not even necessarily that I prefer the sound of flat bass, it really depends on the song. I just can't listen to boosted bass over long listening sessions without fatigue.

 

[Blujackaal]

Yeah, I'm a flat bass kind of guy myself as well. I actually have DT770s I purposefully force a flat bass response out of, despite how much of an especially good job they do with handling bass.
But, it's made very clear (I can't remember by who- Sean Olive?) that the bass portion of the Harman target is the most subjective part. Preferences varied the most for it than any other range of frequencies.
For me, it's not even necessarily that I prefer the sound of flat bass, it really depends on the song. I just can't listen to boosted bass over long listening sessions without fatigue.

I'm bit surprised i like flat bass, Since many past IEMs/full size were bass boosted. But i just can't get enough of how clean flat bass is to my ears.

 

[Cortes]

@Amir,

ASR lacks reviews of electrostatic amplifiers ;-). There's nothing serious on that in the whole internet.

 

[xykreinov]

I'm bit surprised i like flat bass, Since many past IEMs/full size were bass boosted. But i just can't get enough of how clean flat bass is to my ears.

Well, most headphones in general are bass boosted. Truly flat or less-than-flat bass is usually only seen with open-back cans or earbuds that sit outside of the ear canal.

 

[amirm]

@Amir,

ASR lacks reviews of electrostatic amplifiers ;-). There's nothing serious on that in the whole internet.

It is on my todo list.

 

[ROOSKIE]

er4sr also has flat bass? Just like planars and good estats? I'm not sure how it has "more without EQ". And no, *good* planars and estats running off proper source gear do not need very heavy EQ to have good bass. Bass quality depends on more than just FR. Just look at the Campfire Orion. That thing has flat bass on measurements, but sounds limp and rolled off down there when you listen to it yourself. Then you look at an Audeze which also has flat bass and relatively recessed high end, and it sounds completely different. I highly encourage you to actually listen to, say, an LCD2C and then tell me how it absolutely *needs* +8db boost.

One thing people always miss about the harman target is the bass curve is not intended to be a rule. They found different people preferred different quantities of bass, and trained listeners tended to prefer closer to flat. The "official" level in the harman curve is basically an average of all of those. The upper treble is also intentionally heavily rolled off/not really talked about because headphones and headphone measurements vary so wildly in that region it would be impossible to accurately make a target curve for it.

We hear bass frequencies better when the volume is high.
Thus depending on your listening volume you will require a different bass balance along with personal preferences for bass balances.
Additionally I would have thought that the upper trebble in the Harman curve for headphones (not the loudspeaker curve) is rolled off as we can hear those frequencies very well when in the ear (vs poorly when in a room due to tiny wavelengths) and high volumes with them can be very, very damaging.

 

[Cortes]

It is on my todo list.

Great. I suspect results can be epic.

 

[bobbooo]

If you measure the response at the eardrum of a pair of loudspeakers that measure as perfectly flat at the listening position, you will get a response that is fairly similar to the Harman target, albeit with little to no bass boost. If you want a pair of headphones that sound the same as a pair of speakers that are perfectly flat at the listening position, you will want their raw FR to look essentially identical to that of the Etymotic ER-4SR

This is not what is desired though. We want headphones which sound the same as speakers that measure flat anechoically, not flat in-room. This has been shown to be the ideal, neutral speaker response through decades of acoustic research, and as most music is mixed and mastered for speaker playback, we want headphones to replicate this in order to achieve accurate, neutral audio reproduction. Speakers that measure flat anechoically, measure in-room with a ~1dB per octave slope downwards from 20Hz to 20kHz, which is approximately just what the Harman headphone target translates to when this ideal speaker response is measured at the 'eardrum' of a HATS in a typical listening room. See Oratory1990's explanation of all this on Reddit. This all means flat-bass headphones are simply not neutral, despite what any marketing says. They are in fact bass-reduced, in reference to the frequency response that would be heard from an ideal, neutral (anechoically flat) speaker in a typical listening room.