Active sound transmission control using a piezoelectric sensor and actuator on a thin plate is investigated experimentally. The plate made of aluminium covers the opening of an acoustic enclosure where a sound source is located. The exterior acoustic field is measured by a microphone array, which scans a hemispherical surface. The isolation performance of the passive plate is poor at its resonance frequencies. Sound transmission through the plate is actively controlled at the resonance frequencies. A one-sensor one-actuator control system minimizes the sensor output by applying a proper electric voltage to the actuator. Global sound reduction of 15-22 dB is achieved at the first three resonance frequencies by using the same sensor and actuator. Using a sensor at a different location, a reduction of 9 dB is obtained at a higher frequency. The relation between control performance and the coincidence of the responses of the transmitted sound and the sensor is briefly discussed based on the mode decomposition theory.
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