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  • Koss Corporation
  • 4129 N. Port Washington Ave. Milwaukee, WI 53212, USA
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Equipment[add model]

KOSS manufactures or has manufactured the following equipment (click to expand models list):

Dynamic Speakers
Electrostatic Headphones
Electrostatic Speakers
Solid State Amplifiers
Tape Decks

General information [contribute]

Per Andreasen(December 2000): KOSS, the headphone company, also produced an ESL, they made a fullrange and a hybrid, the hybrid was rather special, it was threeway, ESL bass, ESL midrange and the tweeter was a Phillips 1 inch dome.

Christian Steingruber (February 2001): Here is some information regarding the great KOSS ESL of yesteryear . The description leaflet ( only in German) says that model I was a 4-way design, whereas model II was 3-way.

Ein Traum wurde wahr

Seit es KOSS 1968 gelungen war, den ersten elektrostatischen Kopfhoerer der Welt zu entwickeln, arbeiteten die KOSS Ingenieure an der Verwirklichung der Idee eines "full-range" elektrostatischen Lautsprechers, die in ihren Grundzuegen schon seit 1870 bestand. Zu dieser Zeit allerdings machten die vorhandenen Materialien und der Stand der Audio-Technologie die Verwirklichung eines solchen Lautsprechers unmoeglich. Ein unerreichbarer Traum also - bis heute.

Denn KOSS hat das ,,elektrostatische Versprechen in zwei revolutionaren Modellen verwirklicht. Diese Lautsprecher sind so einzig in ihrer Art, dass ihre Einfuehrung zwanglaufig neue Normen fuer die Bewertung von Lautsprechern setzt. Wahrend andere Elektrostaten hoechstens Zwei- oder Drei-Weg-Systeme bieten, wurde beim KOSS-Modell Ia ein besonderes Vier-Weg-System verwendet, das ein Klangspektrum von 32-20.000 Hz umfasst.

Durch die Anwendung dieses besonderen Design hat KOSS den ersten elektrostatischen Tieftoener der Welt entwickelt, der Konzertsaal-Lautstarken erreicht. Zusatzlich wurde eine spezielle Statorplatte fuer den Mitteltonbereich entworfen, um raumliche Verzerrungen auszuschalten, die im allgemeinen bei großen Lautsprecherboxen auftreten. So klingen Instrumente entsprechend ihrer Groeße und Dimension. Die Statorplatten des Hochtoeners und Super Hochtoeners wurden auf die Gesamtprasenz des entsprechenden Durchlassbereich abgestimmt. Das Ergebnis ist eine beispiellose harmonische Wiedergabe und eine breit-gestreute Verteilung der akustischen Energie.

Sobald das Modell Ia - ohne Zweifel ein wahrgewordener Traum - vollendet war, wendete sich KOSS der Entwicklung eines in seinen Maßen kleineren Elektrostaten zu. So entstand das Modell II, eine gelungene Kombination von elektrostatischen und dynamischen Elementen. Das Modell II, ein Drei-Weg-System, verwendet elektrostatische Elemente fuer den Bassbereich bis hinunter zu 37 Hz sowie fuer den Mitteltonbereich von 250-2500 Hz. Um eine akustische Streuung von 1200 im oberen Bereich bis 19.000 Hz zu erlangen, wurde ein dynamischer Kalotten-Hochtoener eingesetzt, der sich als optimal fuer die Gehausegroeße des Modells II erwies.

Hans Zeeuwe (February 2001):Below you will find a translation from the above German article. Please note that both English and German are note my native languages so the translation may rattle a bit. If you can provide a better translation, you are invited to send it to me.

A Dream Came true

Ever since Koss managed to produce the world first electrostatic headphone in 1968, the Koss engineers have worked on the realization of the idea of the "full-range" electrostatic loudspeaker, a concept that dates back as far as 1870. During these days the materials available and the level of audio technology prevented the realization of such a loudspeaker. An unachievable dream until now.

Now Koss has developed the electrostatic dream in two revolutionary models. This loudspeaker is so unique in its way, that its realization will set new standards in the evaluation of loudspeakers. While other electrostatic loudspeaker designs at the most use two- or three way systems, the Koss Model 1a will utilize a exceptional four way system, that has a frequency range from 32 to 20.000 Hz.

By utilizing this special design Koss has developed the first electrostatic woofer that can reach concert hall sound pressure. Besides that a special panel was designed for the midrange frequencies to prevent room dependent disturbances that are usually associated with big loudspeakers. By doing this music instruments will sound according to their size and dimension. The panels for the high frequencies and ultra high frequencies are designed according to the combined frequency ranges. The result is a unequaled harmonic representation and a wide dispersion of the acoustic energy.

As soon as Model Ia - without doubt a 'dream come true' - was developed Koss started working on the development of a -in its dimensions- smaller electrostatic loudspeaker. Thus Model II emerged, a succeeded combination of electrostatic and dynamic elements. The model II, a three way design, utilizes electrostatic panels for the low frequencies (down to 37 Hz) and for the midrange frequencies (from 250 to 2500 Hz). To achieve an acoustic dispersion from 1200 Hz on to the high frequencies to 19.000 Hz a ribbon tweeter was used that proved to be ideal for the dimensions of the model II.

Jon Von Ohlsen (February 27, 2002): Along with the ESP-6 in the early to mid-seventies, Koss produced the ESP-7. This was an ESP-6 with the energizers in a separate box. Since they were also self energized, the volume level would fall off gradually with very soft music. They had white plastic housings, much more compact and streamlined, somewhat like the ESP-9's. I owned a pair for quite a while, having bought them new in '73. I liked the ESP-6, but they were heavy and cumbersome, and the 9's were too expensive (at the time).

John Bruss (October 2002): I was a loudspeaker design engineer at Koss from 1977 through 1984. Your information on the Model 1A is correct but the Model 2 never had a ribbon tweeter (though a reviewer made that declaration which Koss never corrected since Koss considered that a compliment). The tweeter was the popular clear yellowish polycarbonate 1 inch dome unit from Philips that had a rising axial response that closely matched the expected "electrostatic sound" brightness but had, of course, far superior polar response.

I built and offered Koss a prototype of the Model 2 (which I liked much more than the "colorful" Model 1A) which added a layer of acoustic damping material over each bass panel (to control the 50Hz resonance), changed the crossover slightly and used the later soft dome Philips dome with flat axial response to remove the "sizzly" top end. It sounded superb but Koss was approaching Chapter Eleven at that time and esoteric audio was not a priority.

The Model 1 and 1A were 4 way ESLs using multiple panels in each frequency range for both models (panels were sized proportionately for each frequency range). The Model 1 had a symmetrical horizontal panel layout on its baffle while the later Model 1A had an asymmetrical layout and was therefore sold in mirror-image pairs. The bass panels in the Model 1, 1A and 2 all used dual diaphragms with three stators to increase the drive force and lower the fundamental resonance.

John Bruss (December 2003): Koss had four dynamic loudspeakers in their CM (computer maximized) line:

Three of these were reviewed in 1978 and 1979 in Stereo Reveiw and High Fidelity. Koss also had (and still has) two smaller "Dynamite" systems. One has a 3.5" woofer and 1" dome tweeter and the other has a pair of 3.5" woofers and a 1" dome tweeter.

The CM line was designed with the help of Dr. Robert Ashley after Small and Theile (Australia) brought their computer optimized bass box system alignment theory here to America.

Al Imrie (June 29, 2008): The Koss cm1030 speakers were 'built to last' and are a nearly transparent acoustic instrument. Over time (30 + years) the resistors on the crossovers, which contained generous amounts of lead, will have corroded and perhaps the leads will have broken. If you really want to know how these wonderful loudspeakers should sound, a complete crossover rebuild is necessary. Polypropolene caps and lead free resistors are a perfect solution. The coils used (in the "new" version of the crossover, there are two versions) are of very high quality and normally will not have to be replaced. In the "old" version, it is only necessary to reposition the coils so they are at 90 degree angles to the one next to them to reduce distortion. The caps will have dried out and been affected by the heat produced during normal use. Replacing these is equally important. After the crossovers are rebuilt, with good intact drivers in place, there is nothing now available that sound as good as these powerhouses. One source for the parts you will need is www.erseaudio.com. That's where I was able to find everything. Happy Listening!!

KOSS web site (Febuary 4, 2010): Today, the Sound of Koss can be found in the home, on the go, at your desktop or in the air. There is a quality Koss Stereophone for every personal listening need.

Refurbishing & modifications[contribute]

Chris (March 24, 2009): I have a KOSSfire model110 With a dual tweeter, mid range tweeter, and aftermarket 1oinch 380w max Visonic Subwoofer. I also Have the original 10inch KOSSfire speaker. Comes with high frequency controll knob.(PRETTY LOUD)!

Chris(human)LOL! (March 24, 2009): This item is available for sale or parting, email me, if you want (partypants666@live.com).

Forum topics on KOSS

The following topics regarding KOSS in general can be found in the forums. Topics about specific models can be found on the model pages. If you want to start a new topic, click here.