I am a happy owner of the ESP-950s, and have experienced none of the problems others have reported. These phones have the deepest bass I have experienced with any phones, and in fact exceed the performance of most speakers even when augmented by subwoofers. The treble is smooth and extended. A unique combination of pleasure and revealing detail, two elements which usually conflict.I prefer them to the Stax SR-5's, which are my other phones.
The 950's are also the most comfortable phones I've ever had, exerting only minimal pressure on the skull, probably because their superior bass output does not require a perfect seal.

The phones come packed in a beautiful glove-leather case. A battery pack, which takes 6 "C" cells, and a wall-wart supply are also included. Suggestion for improvements:
1) The concentric left/right volume knob is clumsy to manipulate, and should be replaced by separate volume and balance.
2) There should also be a 6 AA cell pack, which could be used with NiMh batteries.

While its difficult to add any clarity to SB's review since I really don't know what "do dynamic" means, I will try to shed some light on how they perform since I've owned them for 2 years now.As far as dynamic ability is concerned they are beyond reproach. The amount of clean gain available is striking. This, combined with excellent low level dynamic ability brings out a certain amount of "breath" in recordings thats missing in many lesser phones and certainly most speakers.Their sonic qualities ,in whole, are without question and, quite frankly, I can't imagine anyone faulting a properly fuctioning pair as far as their sound. I mention "properly functioning pair" since that is the only real fault with this product. There have been some reliability issues which have been addressed my myself and others that need to be considered.Fortunately KOSS is aware of them and is working on a fix.Overall, an amazing headphone for, what is I consider, a bargain price.

Flat frequency response, uncompressed dynamics

Can "squeel" of hairs get between the stator and the HV diaphram - just remove the hairs and it is OK.

These are excellent headphones; however, like all electrostatic products they are a bit "special" and require a technically astute user. The biggest problem is that hairs can protrude through the foam covers and cause small discharges between the stator (to which the high voltage audio signal is applied) and the diaphram (which is charged to a high voltage at approximately constant charge). To solve this problem, one simply removes the hairs, which never seems to be a problem. Other than this small "defect", my headphones have been working perfectly for about 5 years. They are comfortable, linear (in dynamics and frequency response), and, overall, superb. At $500 they were an excellent value. I have been a user of triamplified Dayton Wright electrostatic speakers for well over a decade and am a professor in materials science specilizing in high voltage dielectrics, so I have the background necessary to deal with both.

Similar Products Used:

Dayton-Wright Electrostatic Speakers

Good quality sound for the price, good accesories.

squealing

The sound is not the last word in electrostatics but is probably better than any dynamic system,(which should probably be called magnetic or coil system, since there is nothing inherently dynamic about a magnetic speaker). The portable accessories make this very appealing and useful as a back-up system on trips. However, Stax has also produced a compact portable system which I have not heard.
Like some other reviewers, I had squealing problems, otherwise I would rate these phones at a 4 or 5 stars I sympathize with some reviewers' frustration and anger. Certainly Koss replaced my units, I think four times under their commendable lifetime warranty, but what a waste of time and money! The problem is I believe a very simple and fixable design error by Koss: Where the cords leave the earpieces, they come very close to the open, high voltage contacts on the transducers and current can pass down the cord, giving the squeal. How do I know this? Because I watched little sparks jump across when I looked at the unit, opened, in the dark. If you can pull the cord away a small amount, the problem will probably disappear. However, the space there is very constricted.
This type of problem is probably sensitive to moisture in the air, contaminants on the cord and the spacing of the cord, so it is not surprising that some units do not show this, or that Koss cannot recreate the problem in a dry air-conditioned room. Also the squealing is faint and would not even be noticed on much pop or rock music.
Fortunately, my last set, while initially a squealer, has since settled down.
That said, while Koss deserves credit for its life-time warranty, it also deserves a kick-in-the-butt for not solving the problem. I own or have owned at least 12 sets of electrostatics, including three sets of Koss' and have never encountered such a persistent problem.
On balance, a good entry level system, if you are prepared to chance the squealing problem.

Similar Products Used:

Koss ESP 9, ESP 6a, Stax Sigma, Stax Lambda Signature, Jaecklin and others.

Koss finally sent me yet another new pair of ESP-950's about two months ago; this is my 5th pair from them. We have moved, so I did not have a whole lot of time until the last two weeks to listen to them. As of this date I have not heard the notorious "squeal" problem with the headphones. I am glad that others have contributed meaningful reviews to this page. I agree wholeheartedly with them; the sound of these headphones constitutes a real value (if you have a properly working pair--a real consideration). I would add the following minor criticisms:
1. The "RCA Phono" input jacks are surfaced mounted on the pc board inside the "E-90" energizer unit. This is a poor design for this type of product as (especially using audiophile grade connecting cables) a plug could loosen or break the jacks upon insertion or removal--must be careful about this.

2. The energizer unit was designed to be all things to all people. Perhaps a unit specifically targeting audiophile home systems would be in order (a tube driven unit?).

3. I agree that the volume/balance knob is also a poor design. The control does not track evenly and when you change the volume you also have to adjust the balance as that changes too.

Having said the above, I again say the sound of the headphone is a good value. My experience with Koss in this ordeal, especially with Ms. McCurdy, leaves this "loyal" 30 customer with the opinion that I will never again purchase a Koss product.