Reseach On Length-limited Parametric Loudspeaker

Compared with traditional parametric loudspeaker, length-limited parametric loudspeaker can generate audible sound beam with both direction and effective distance under control. In this paper, length-limited parametric loudspeaker is considered feasible by means of analysis and numeric simulation. And a new method, adjusting combined weight factor of the length-limited parametric loudspeaker, is proposed to control the effective distance of audio beam. Moreover, some basic parameters are calculated and a modulating method is chosen to realize length-limited parametric loudspeaker. What’s more, experiments on length-limited parametric loudspeaker are carried out.It is concluded that the phases of parametric loudspeakers with different carriers in frequency are the same at the same distance in the propogation direction with the quasi-linear assumption, after axial sound pressure of these parametric loudspeakers is simulated and analyzed. According to the basic theory of length-limited parametric loudspeaker, the initial difference of phase is selected. And the ratio of sound pressure is calculated as the initial combined weight factor. With these two parameters, length-limited parametric loudspeaker is simulated, and finally combined weight factor and difference of phase are obtained.Based on the numeric solution of KZK equation in time-domain, axial audible sound, which is generated by parametric loudspeaker with different signal pre-processing method, such as double-sideband AM(DSB), single-sideband AM(SSB) and square root AM(SQRT), is researched when different modulation is used. Then, according to the theory of length-limited parametric loudspeaker, the double-SQRT method is chose as the signal pre-processing method of parametric loudspeaker. And DSB-PPM is used to realize this pre-processing method in FPGA platform upon the analysis on DSB-PPM theoretically.Moreover, the audible sound field of length-limited parametric loudspeaker is researched through quasi-linear simulation with different initial difference of phase and different combined weight factor. And a new method is proposed to control distance of audible sound according to the result, which means, the spreading distance of audible sound is controllable by modifying the combined weight factor.According to theoretical analysis and simulation, transducer array is made for length-limited parametric loudspeaker, and the signal pre-processing method of length-limited parametric loudspeaker is realized on FPGA. After the whole length-limited parametric loudspeaker is finished, the effect of length-limited is significantly observed in the experiment, thus making it clear that the length-limited method is effective.