Polycom SoundStructure C16 Design Manual page 452

Design Guide for the Polycom SoundStructure C16, C12, C8, and SR12
The same approach can be taken with the lectern microphone, creating a
submix called "LecternRef" that includes the reinforced wireless microphone,
the remote audio sources, and the program audio. The new matrix will appear
as shown in the following figure.
The AEC reference for the lectern mic can then be set to the "LecternRef"
submix as shown in the next figure.
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