PB, I did not make myself clear. I dont like the Telex/Sennheiser lightweights because although they have no noise attenuation they seem to inhibit speech sufficiently to force me to were them one ear on/one off. Our company sadly does not use the intercom.
I have seen a Sony headset that is clearly based on the design of my Hi-fi walkman headphones which I am sure would be ideal if they could be made to work with an aircraft comm system. Hence my specific inquiry about impedances.