My first impression of these headphones was lackluster to say the least, They are lacking some serious tuning, which the headphones could greatly benefit from. The sound signature is mostly flat, with some mild lower bass roll-off, but quite serious mid to upper treble roll-off. Even though i'm not a treble head, and am quite sensitive to treble, the lack of treble really put me off these headphones. I can't listen to them without using an EQ to boost the treble response. But I must say, when you do, do some personal fine tweaking of the sound, these headphones really open up. Make no mistake, these are electrostats, but ones with an obvious lack of pre-tuning of the sound.
The overall signature is dry and flat, almost somewhat muffled even, but with the right tuning these could even sound favorably against the Sennheiser he 1. And yes, I've listened to those headphones, ironic that I didn't really favor the sound signature of those either. When compared to the Sennheiser he 1, those have more speed, authority in the bass with a overly warm sound, coupled with a shimmering sparkling top end. These though are dry, flat, and pretty much boring. But once you EQ them they come to life. If you don't want to EQ a headphone out of the box or are a treble head, or basshead, don't bother. But if you're willing to take the time to fix the sound on these, then by all means. I do regret buying these, but they are my first pair of electrostats. It helps that the midrange is pretty much flat, so these will aid me in checking my mixes.
Build quality is fine, it won't impress you, but they are as light as a feather and seem relatively durable.
Comfort is excellent. My only complaint is the fact that the headband mechanisms don't have any detents, which can get really frustrating when they slip a little while adjusting.
How do these compare to my beloved oppo pm 3s? They are both pretty flat, pm3s are boosted in the upper mids a bit, which makes for a more organic and fun sound. The only flaw with the pm3s sound is the highs and the fact that they are closed back. Other than that the pm3s are possibly one of the best headphones on the market. But when EQ'd the esp95x become their own monster. Honestly Koss needs to update these headphones. With a new more modern design, a tweaking of the sound signature, these headphones could easily rival a Sennheiser he 1. In terms of value at least. The he 1 is 50,000$, this headphone costs 500$. But I don't feel that the potential is all that far apart. The sound is just really unrefined. Also the pads are horrible!, I'm going to have to spend 90$ on the custom leather pads to close the gap between the back of my head and the earpads. The leather pads should even out the bass response and further refine the sound signature.
That's all I really have to say. If you're not gonna EQ these stay away. Or if you're fine with a dry and muffled sound by all means go ahead.
One more thing, I remember listening to the audeze lcd4, and it having the same exact problem with the highs as these headphones. The highs on that headphone were essentially missing, the soundstage was also unnaturally wide and a bit too narrow. These esp95x headphones have about the same soundstage as the Sennheiser he 1. I really think the custom leather pads will dramatically improve the sound of these headphones. We will see soon. So I'll say it again, these headphones have a lot of potential, but you're going to have to go the extra mile to get them there.
I'm noticing an overall improvement in the balance of the sound with time, it's not huge, but it's there. I think these headphones really need time to settle into themselves. The sound seems to be evening out ever so slightly with frequent use. Perhaps this is an electrostat thing, and the transducers just need time to adjust to being used so the response can even out and become more responsive. The highs definitely anyway. I'm also noticing more slam and impact from the bass, it's becoming more responsive to songs that require more oomph like electronic music. This is all with the EQ I made turned off. We'll see how much more these will improve with frequent use.
It would appear the earcups suffer from internal resonances. This is probably a result of the earcups plastic not being thick enough, the result being a muffled sounding upper mid to high response. Another reason why these headphones need an updated design. I wonder if someone could 3D print new, more sturdier earcups that wont resonate. If you place your hand or finger on the earcups when you play music, you can feel the internal resonances playing out. On my oppo pm3s, which are heavily dampened internally, this is absolutely non existent. Still though, the sound seems to improve with use, these are starting to live up to their price tag sound quality-wise. I no longer feel the need to boost the highs, as doing so at this point will invite sibilance and ear pain. The highs have opened up enough for me to be satisfied with them. Soundstage width and depth has improved as well. Almost every listen incites goosebumps and makes me stop whatever I'm doing to listen and become immersed in the music. Still though the build quality leaves much to be desired, resonating earcups should be a no-no at this price, nethertheless I will try to be satisfied with my purchase and get the most out of it. If there are any 3D printer peeps out there, just know this is a top grade sounding headphone, that could really use a nice non resonating-new set of earcup enclosures.
I am adding a star, as the sound quality has improved with further burn in, now I can safely say these are headphones befitting even a 1,000$ price tag. I will leave off one star for the awful build quality and horrid stock pads which should be angled leather pads. It would be nice if Massdrop would release angled leather pads for these headphones, as paying 90$ for the custom leather pads from fang audio does not please me in the slightest. But for these it will be worth it. After all I want to get the best out of my investment.