Headphones are actually as old as reproduction of sound itself but they remained a mostly professional tool for use in communications and recording right up until the 1970's, primarily it seems because musical and voice reproduction was more of a social phenomenon than it is today. Apart from a minor fad in acoustic headphones for use with gramophones in the 1920's and the headphones distributed for use with crystal and low output radio receivers into the early 30’s out of necessity, since the lack of amplification meant that they could not drive speakers, the first headphones actively marketed to consumers as a feature on their own where actually intended for use with early television sets. These were intended more to isolate the first generation of TV addicts from the rest of the family than to provide high quality aural experience to the end user, this was obviously before TV became the family life, and this isolation factor is what drove headphone design for the next couple of decades.
High end electrostatic headphones intended for music reproduction where introduced in Japan in the mid 50's, with dynamic stereo cans pooping up in the USA at the end of the same decade and in a similar time frame high end professional units intended for studio work start being produced in Europe, however these where all closed back models that ultimately sacrificed sound quality and wearer comfort in favour of maximum attainable isolation from their immediate surroundings and it is not really until the introduction of the revolutionary Sennheiser open models in the late 60's that we start to see headphones as a popular hi-fi or a personal audio phenomenon.
There were only 2 models sold under this brand as far as we know, the rock bottom priced Can S and the only slightly better Can S2, both are closed back units sold to the DJ market. The company never gave out any audio specifications for the Can S, simply the mechanical spec of W:22.7 x H:20 x D:5.7 cm @ 500 grams for the Can S although we managed to scrape together the basic audio/electrical spec by looking into related manuals for bundled products which gave us: Frequency range 20Hz to 20kHz, impedance: 32 , supplied cable length is 1.8 metres.
The Can S model was sold as much as part of bundles like the Home Mix TT2000M as on its own, the model was renamed Can S-1 in 2007 but remained the same electronically and mechanically. The Can S2 is somewhat better having a padded headband and a published specification an all; Max Power input: 100mW. Sensitivity: 100dB. Cord length: 2.9 meters. Supplied with a 3.5mm jack and an 6.35mm adaptor. W:22.7 x H:20 x D:5.7 cm @ 500 grams and was made available in silver or black and came supplied with a "how 2 mix" interactive CD-ROM. Introduced in 2003 and appears to have been take off the market in 2007 or thereabouts.
Infinity Made the ME10D combination of electrostatic headphones and energiser that was connected to the speaker terminals of an amplifier and could drive a pair of headphones, all of the examples I have seen of this unit have had the energiser in an excellent condition but the headphones themselves have all been degraded fairly severely considering the age of the product (ca late 70's). In particular the headband, which typically has lost most of it's plastic covering on top as on the bottom so this is not an indicator of wear, the ear pads have also been bad although they look fine there has been so much degradation of the padding inside the pads that they are uncomfortable and the isolation they offer is minimal, the latter affecting the sound quality.
Micro Seiki Made a small range of electrostatic headphones, while high quality these were expensive when new and are difficult to get hold of second hand.
NAD Often forgotten that this company used to be a supplier of high end headphones in the 70's, they had a range of 5 models in 1976 and the most expensive of those was the electrostatic Model 20 e which had a RRP of close to 50£, considerably more than most people spent on an amplifier in those days. Note this was when the company was still primarily German and these are very rare in the UK, but cheaper units like the electret Model 16 do crop up for sale in Germany from time to time. These headphones are believed to have been OEM designs from Stax although it is possible that the cheapest models came from other suppliers.
In the early 80's the company did supply some fairly budget open type units, by this time there had been a change of ownership of the brand and they were mostly selling in the UK and Scandinavia but they seldom turn up for sale since the foam covers rot and they tend to get thrown away. These were cheap enough for the company to be often given away as promotional items BTW.
The company started manufacturing headphones and headsets in the 1950’s and was for a long time the only manufacturer of quality headphones in the USSR, however their product line remained primarily intended for communication usage until the 1980’s when out and out hi-fi models like the TG-12 and TGS-2 were introduced, nota bene, the TG12 and TGS2 looked absolutely identical externally, the only difference was in the specification. The company exited the home audio market in the 90's but still is one of the world’s largest manufacturer of professional headsets.
Revox Has through the years had quite a few models on the market but as far as I can gather none of them were made by the company itself, some 70's models were rebadged Precide models and later ones like the RH 3000 were actually top of the line Sennheiser models and I do seem to recall a model that appeared to be made by AKG.
Sennheiser Well the HD-450 was never a top of the line model, nor in fact anything near it, but like the current models from the company you could buy it almost anywhere, and one day in the late 80's I was in a small recording studio in Iceland that had on one hand a pair of massive JBL monitors that made every track sound like Sly'n'Robbie and on the other hand the horribly tinny Yamaha NS-10 nearfields, and all mixes were going wrong. I needed something more neutral and I needed it at once and I ran out (studio time costs money you know) and found a electric household store nearby and bought the most expensive model that they stocked. The resulting mixes were so good that I started to take those cans with me everywhere, mind you the 450 was not a perfect design by any standards, it could be more efficient for one thing (perhaps a good thing for my ears that it's not), but it has turned out to be absolutely bullet-proof, it has taken abuse that I have seen no other device take, repeatedly walked on and thrown about in addition to having travelled with me wherever I go, in fact the mechanical design is so good that while I would not buy it in preference over the current line-up I consider it to be preferable since the phones collapse under stress, the current models have just 1 cord leading to the unit this means that they cannot be taken apart completely, while this is ergonomically better it also means that they are not as resilient.
Stax The company itself has a nice history page that has technical info on some of their older headphones, note also that although the company currently only makes electrostatic models they had cheaper electret models on the market in the 80's and early 90's and while old electrostatic models are well supported and often represent a good second hand buy you should watch out for individuals trying to peddle the inferior models as electrostatics. Those cheaper models are missing from the Stax history page BTW.