The Analysis And Control Of The Sound Field Of The Phased Loudspeaker Array

Phased array loudspeaker is a system consisting of several loudspeakers arranged in a certain geometric configuration.By changing the geometrical parameters of the system and the electrical signal parameters of the loudspeaker elements,specific sound field can be formulated.In this thesis,we focus on the theory of sound field and phased array signal processing of phased array,which provides theoretical and practical basis for sound field control of loudspeaker system.According to the basic theory of sound field propagation,the far-field sound pressure directivity function of the loudspeaker array,the directivity graph and the directivity parameter describing the sound field characteristic are firstly studied.Furthermore,we discuss the different sound field characteristics of point source,linear speaker array,arc type loudspeaker array,linear high and low frequency combination array and ordinary plane array and Bessel surface array.These formed sound fields concentrate energy on the main beam so that they may radiate farther away.The array beam deflection is achieved using the multi-channel equalization delay method.The main beam direction is deflected up and down by 10 degrees in the direction of the vertical line of the linear speaker array.The amplitude suppression of the side lobes is achieved by 20 dB via Matlab simulation,and the sound pressure level attenuation of 5 dB is achieved in the experiment.The constant beam width of the linear speaker array is analyzed by using the high and low combined linear array method.The main beam width is constant in one octave of 100 ~ 200 Hz.The finite element simulation of simple array and complex surface array is carried out by using Matlab and Comsol software.The effects of array formation,array element number,array element spacing,sound source frequency and other factors on the main lobe width,side lobe and direction of phased array loudspeaker are studied.The advantages and disadvantages of linear speaker arrays,arc-shaped loudspeaker arrays,high and low frequency combined linear array,rectangular array,and Bessel array are compared.The high and low frequency combined linear array has a smaller main beam width and can achieve constant beam width in a certain frequency band,but the side lobe increases.Although Bessel array's performance is good,it is relative complicated during the engineering implementation.The experimental platform for phased loudspeaker array is set up using Xilinx Spartan series of FPGA as a central processing unit and TD7294 digital amplifier as a driver.The multi-channel phase delay method is used to realize the beam deflection.The side lobe suppression is realized by changing the weight coefficient.The linear combination method is used to keep the main lobe's width constant in the frequency band,and the system response of the high and low frequency array is realized by using FPGA internal delay and adding unit function.The test platform for the loudspeaker array's sound field is built to measure the sound pressure and directivity of the far field.The experimental results show that the sound field of the phased array can be controlled and the theory and method of signal processing proposed is verified.