Transient response of flat-panel distributed mode loudspeakers

Abstract

The acoustic impulse response of a loudspeaker must have short rise and decay times to provide accurate reproduction of signals with fast transients, such as human speech. In a flat panel distributed mode loudspeaker (DML), the transverse bending waves that are the primarily source of acoustic radiation, propagate across the panel at finite velocity. Therefore, regions of the panel more distant from the panel driving point(s) radiate sound at later times, which broadens the DML’s acoustic impulse response. Furthermore, bending wave propagation in a rigid panel is dispersive, with a wave velocity that is proportional to the square root of the frequency, which creates additional distortions of signals with fast transients. Mechanical simulations and scanning laser vibrometer measurements of glass panel DML’s clearly illustrate the delayed radiation and dispersion distortion mechanisms. Furthermore, measurements of the acoustic impulse response of DML’s are in agreement with simulations, which provides additional evidence that the identified mechanisms are a major source of audio distortion in DML’s.