Development of an Acoustic Filter for Parametric Loudspeaker in Air

In this study, an acoustic filter for a parametric loudspeaker for removing the spurious signal generated by the nonlinearity of the receiving transducer was developed. A 16-mm-diameter aluminum plate was set in front of the transducer to attenuate ultrasound by more than 15 dB on average, with negligible effect on the audible sound. Experimental results demonstrated that, in the near field of the parametric loudspeaker, the spurious signal was dominant in the measurements as the sound pressure levels of the primary waves were more than 120 dB. However, the audible sound generated by the parametric loudspeaker can be detected even without the acoustic filter in the far field. (C) 2011 The Japan Society of Applied Physics