Philips SBC 3178. A rebadged AKG; some say the K 260, but I've not seen proof. Sound isn't very good.
The two known PMB (Peerless Mikrofon-Bau) 55 mm orthodynamic drivers from the late 1970s.
90 holes in five rows, with or without steel plates that improves magnetic force. Found in PMB8, PMB80, PMB100, Dual DK830 and some Telefunken TH700.
60 holes in four rows. Found in B&O U70, Magnat RT10 and some Telefunken TH700.
More holes means larger effective "playing" area, but less magnetic power. In the end the difference might not be so large, but the 90 hole version is a bit more efficient and sounds better to my ears.
Close-up of the back of the Sony MDR-CD1000 bio-cellulose driver. Apparently they used a base to grow the bio-cellulose on (you should be able to discern the texture in the lower hole), but I haven't seen any documentation on what material it is. Could be microfibre. Anyone know? The MDR-CD1000 was introduced in 1991 together with the CD3000, in the wake of the legendary R10 (1988). This also had a 50 mm driver, but was 40 ohm compared to 32 ohm for the CD1000 and CD3000.