Defining the Parameters of Truncated Square-rooting DSB for Parametric Loudspeaker
Ying Wang, Min Chen, Hui Li, Zhe Zhou · 2007
Parametric loudspeaker is an instrument which is capable of transmitting acoustic signals in a highly directional beam. The theory of sound reproduction for this system is based on nonlinear interaction of ultrasonic waves in air. The demodulated signal is proportional to the second time derivative of the square of the ultrasound envelope. Then truncated square-rooting DSB (double sideband) is proposed, but many factors are considered in each parametric loudspeaker, such as the carrier frequency, the characters of filters and the modulation index. Take example for our designed system, the carrier frequency is the primary factor we considered, and it is should be close to the resonance frequency of transducer. The band-pass filter design method for the truncation of bandwidth is presented, and the modulation index m=0.7 is chosen as a tradeoff of SPL (Sound pressure level) and THD (Total harmonic distortion). Finally, the directivity of the loudspeaker is high as shown in the result.