The EX90 Admin Guide states, that either a Headset or the Cisco TelePresence Table Microphone 20 can be connectet to the 3.5mm input on the rear.
These two microphone types are quiet different:
Headset: has a 3.5mm mono connector plug, asymmetric output and needs a PC-Soundcard-Style Power Supply.
CTS Mic: has a 3.5mm 4pin plug, symmetric output and needs a 12V Power Supply
Can anyone from Cisco tell us something about the technical backround, how the EX90 handles these two very different Microphone types?
And is there a way to use the Headset Mic only, but keep the output on the internal speakers?
You are correct these are quite different mics. I cant offer you much in the way the EX90 handles these two different types, just that it does work but only on EX90 and not EX60.
Here are the specs for the Table Mic 20:
CISCO Performance Mic 20 Specifications
As for your question regaring using the Headset Mic only, but keep the output on the internal speakers, this is not possible.
thank you very much. Seems, that you´re familiar with this theme, so I´ve got some other questions and inputs on that