Ok, nice to hear that you are interested in those old development. To be honest, I'm really thinking that this product is outstanding till now in sound performance. However, the comfort to wear is poor, but this was never the main aim at this time.
The product developed before the K1000 was the K240DF. Meaning designed for the diffuse field. In simple words, the acoustic is designed so, that measured on the ear entrance the frequency response shall be the same as sound from far field listening to ideal speakers and sitting in a listening room.
After finalized the K240DF we recognized a quite large community especially in the German region which liked that sound adjustment.
On the other hand side, we developers was not satisfied, because the sound performance was very depending on the users ear and also we "hate" to wear closed headphone because of the heat surrounding the ear after a while.
Therefore we agreed to design a headphone without that disadvantages.... That was approx. 1985 when the K1000 project idea was born.
It was clear to us, that due to missing sound pressure chamber in front of the ear, the speaker driver has to deliver a very low resonance frequency and relative huge displacement. Also the effective membrane surface has to be very large and very stiff and lightweight too.
The development of this simple looking membrane took approx. 3 years, 'cause no proper working simulation programs exist at that time available for us.
The magnet/coil system was always questioned and alternatives like orthodynamic systems and electrostatic drive was also considered. However, the classic dynamic drive won. This was because of the special design of the radial magnet system of the K1000 which works very effective and could be designed very tiny. Therefore the effective acoustic inductance of the complete K1000 was lower than any other driver system we benchmarked. I other simple words: When measuring on the ear entrance wearing the K1000 the sound coming from free field, it's almost the same as without the headphone.
.... Any specific questions more ?