Synchronization of Organ Pipes

We report results on the synchronization of an organ pipe either by a second pipe or by a loudspeaker, positioned side by side. Classical theory suggests oscillation death for the synchronization of two organ pipes. With our measurements we clearly exclude this scenario. Rather, we identify the aeroacoustical coupling by the oscillating wind sheet at the pipe mouth as the source of a self-regulation of the phase of the organ relative to the driving source. In the case of two almost identical coupled organ pipes, the oscillation is antiphase such that they silence each other, in the case of a loudspeaker driving the organ pipe, an in-phase movement is observed at the edge of the synchronization region, which yields a much louder sound of the coupled system at the frequency of the loudspeaker. This is a way to stabilize an acoustical sound source by a minute signal the loudspeaker can be up to 30 dB weaker than the organ pipe, but still forces the instrument to follow it.