I was wondering, what would happen if a person was to stand at the center of a circumference of radius $R$, where a loudspeaker playing a musical note in the audible range ($C_5=523 Hz$ for example) was rotating at a tangential velocity equal in magnitude to sound speed?
Would he perceive any change in the pitch of the loudspeaker? Or would the sound waves destructively interfere at the center?
What would change if the loudspeaker was shut down so that it would be completely silent (but still have volume)?