An oblong button.

A6/A8 speakers have no special button for the microphone priority function. The off function is: press and hold the single loop button for three seconds (that is, the oblong button) to turn off the microphone priority function.

Microphone priority is a function of the public broadcasting front-end equipment. When the microphone volume reaches a certain level, the background music is immediately reduced. The amount of reduction is controlled by a sensitivity knob.