There are two different microphones shipping with Macintosh computers: Omni and PlainTalk. They are both require a power or voltage source to operate properly. The power source for these microphones is provided through the microphone connector when you plug the microphone into the connector on the rear panel of the computer.
The PlainTalk microphone that ships with Macintosh AV computers will not work with the AudioVision display because the display connector does not provide the power the microphone needs.
The proper microphone for the AudioVision Display is the Omni microphone. If you want to use a PlainTalk microphone, you must connect to a computer that supports it.