In a piezoelectric electroacoustic transducing device which is to be incorporated in an electronic apparatus such as a portable telephone, and which is used as a sound source, the sound pressure of the low-frequency range is improved, the productivity is improved, and acoustic characteristics are stabilized....http://www.google.de/patents/US8107650?utm_source=gb-gplus-sharePatent US8107650 - Piezoelectric electroacoustic transducing device
