There's some discussion of these electrostatic 'phones in various threads, and reviews, but I thought it would be worthwhile to dedicate a thread to the ESP-950.
The ESP-950 doesn't get the respect it deserves, in my opinion. It doesn't have the brand cachet of Stax - Koss ESP-950's are the only current electrostatic headphones from Koss, whereas Stax makes ONLY electrostatic headphones and their driving devices. (Electret headphones are also a kind of electrostatic headphone.) So, since Koss isn't associated only with high-end products the way Stax is, it can't get no respect....
Koss has a long history of electrostatic headphone development, going back to the late 1960's I believe. I bought a pair of Koss ESP-9's in 1970, and drove them with a Harman-Kardon Citation 12 power amp / SAE Mark XXX preamp. Source was an ADC XLM cartridge or a Shure V15 in an AR XA turntable, plus an Akai GX365 open reel deck running at 7.5 ips. With Scotch 207 tape! Hahahahaha I even remember doing the bias setup for that tape on that Akai deck. That was a LONG time ago!
But the ESP-9's were arguably the best headphones of the day. Stax had the SR-1 but I never saw them in the US and reports I heard said that the ESP-9 was superior.
There were the ESP-6's which are not the greatest- the earcups have have built-in step-up transformers and derive bias from step-up / rectification of the audio. They weigh a ton and don't sound as good as the ESP-9's. The ESP-6's predated the ESP-9's I believe.
The ESP-9's were replaced by the ESP-10's, which had a more upscale appearance and were said to be better sounding, and although a friend of mine has owned them for years and swears by them, I have never spent any time listening to them.
All of these earlier Koss electrostatics were closed designs.
Here's some info on the Koss electrostatic stuff, including reviews back from 'the day.' http://wiki.faust3d.com/wiki/index.php?title=Koss_Electrostatic_Line_Overview
Now we come to the ESP-950's. They are an open design, and come with an amplifier instead of just a coupling transformer / bias supply which you attach to your speaker amp, as the ESP-10, -9, -7 and -6 did.
I haven't compared the ESP-950 to earlier Koss efforts, but I DO have Stax SR-007 MK II's, and a pair of Stax Lambda Pro Signatures. (I also had a pair of Lambda Pros, but I sold those.) I would say the the ESP-950 is in the same class as the Stax 'phones, though it does sound different. My ESP-950's have a Stax cable on them, and I've only listened to them through my Stax SRM-1 MK I and my Stax SRM-T1. Their sound is VERY GOOD, though different from the Stax.
My comparison in a nutshell:
- ESP-950 has more bass impact than Lambda Pro Signature, a warmer midrange and although the Koss have a lot of inner detail, they do not offer the exquisite level of detail available through the Lambda Pro Signatures.
- ESP-950 sound as 'clean' as the SR-007's but have a more colored sound, the SR-007's sound closer to natural. That is to say, the ESP-950's distortion is way low and ringing, energy storage, and so on is low, but there is a bit of a midrange emphasis from the Koss while the SR-007's seem more closely balanced to offer a neutral sound. Keep in mind, of course, that the SR-007's cost roughly three times the ESP-950's street price, and at that price the ESP-950's include a decent amplifier. (The Koss amp is good sounding, not as good sounding as the Stax I mentioned, but still is not bad. And the Koss amp runs off batteries... which can be useful at times.)
I would have to say I prefer the Koss to the Lambda's by a slight margin, largely because they offer better bass impact. And while the Koss ESP-950's are more comfortable than the SR-007's, I have to say that I find the sound of the SR-007's to be superior in many ways.
If you look at Purrins thread covering CSD plots, you can see that the ESP-950 performs quite well. http://www.head-fi.org/t/566929/headphone-csd-waterfall-plots/30#post_7724844 and Purrin mentions that he likes the way the ESP-950's sound.
So, I ask, why don't the ESP-950's get more respect? Is it because they're from a company who doesn't really have the high-end market in their sights? Are the Koss ESP-950's falling victim to the if-it's-not-$5,000-it-can't-be-any-good snobophiles?
I admit, they don't exude build luxury like the top-of-the-line Sennheisers or Staxes, but their sound is somewhere between really very good and excellent, and isn't SOUND what it's all about?
Edited by milosz - 7/13/15 at 2:48pm