Synchronization of sound sources.

Sound generation and interaction are highly complex, nonlinear, and self-organized. Nearly 150 years ago Rayleigh raised the following problem: two nearby organ pipes of different fundamental frequencies sound together almost inaudibly with identical pitch. This effect is now understood qualitatively by modern synchronization theory M.

Piezoelectric two-layer stacks of cellular polypropylene ferroelectrets: transducer response at audio and ultrasound frequencies.

Piezoelectric cellular polypropylene films, so-called ferroelectrets, are assembled in a stack with two active transducer layers. The stack is characterized with respect to its linear and quadratic response in a frequency range from 1 kHz to 80 kHz. A relatively smooth frequency response in the sound-pressure level is found for the individual layers as well as for both layers driven in phase.