Rotel rh-930 headphones, can anyone tell me about them?

[taymat]

For £20 from ebay I bought them just out of curiosity. These have no drivers visible behind the grills just metal plates. They're from the 70s I think and have a switchable impedance adaptor. Can anyone here tell me more about them, they're very flat sounding. Thats a nice way of saying they sound boring, there's not much bass or treble but they respond well to eq on a karma. Anyway here are some pics, please tell me more someone:

 

[Jose Perez]

As a matter of courtesy for those with slow connections could you please resize your pictures? Thanks