An experimental investigation about parameters’ effects on spurious sound in parametric loudspeaker

The spurious sound in the measurement of the parametric loudspeaker is resultant from the nonlinearity at the receiving system caused by the ultrasonic waves with high amplitudes. It may provide a misleading result, especially in the nearfield, where the parametric array effect of the parametric loudspeaker cannot be easily observed. In this study, to eliminate or alleviate the effect of the spurious sound, an in-depth investigation into the spurious sound in the parametric loudspeaker is carried out experimentally by adopting an index of a ratio between the spurious sound and the demodulated difference-frequency sound. A relation between the above ratio and four main parameters, i.e., the amplitude of the primary waves at the source, the radius of the ultrasonic emitter array, the frequency value and the observation distance, is obtained. It exhibits a good match with the well-known theory described by the Gaussian-beam expansion technique. The threshold to ignore the spurious sound in the measurement of the parametric loudspeaker is also established.