The basis of basic theory of acoustics, technical parameter of loudspeaker and intrinsic parameter of phase-reversing voice box, this essay is intended for carry out the deduction of calculating formula for phase-reversing voice box, thus for design the proportion and scale of phase-revevsing voice box.

Due to the unceasing increase of difficulty and dissension brought by car-backing in our daily life, it s inevitable for the research of intelligent car-backing system, however, it!s one of the keys for the control of steering wheel!s angle displacement in the realization of cars precise backing.