The Harmonic Distortion Of Loudspeakers Caused By Diaphragm Vibration

The harmonic distortion is an important factor for the sound quality of loudspeakers. The total harmonic distortion, second harmonic distortion, and the third harmonic distortion are important parameters which need to be measured during the process of designing high quality loudspeakers. Many studies have been done on the problem of harmonic distortion caused by the nonlinearity of driving force and support system. And literatures about the problem of harmonic distortion caused by the nonlinear vibration of diaphragm are very few. During the graduate school, based on reading relevant literatures, main studies have been done as follows.1. The linear vibration differential equations of axisymmetric shells of revolution was derived. The resonance frequencies, modes and the SPL curve of a cone loudspeaker been calculated by using the differential equations, the boundary conditions, and the finite difference method. The results were validated by comparing with the literature [3].2. Starting from the Hamilton’s principle, by using the linear displacement patterns of the shell to discrete the continuous body, the nonlinear vibration equation for thin axisymmetric shells been derived. The coefficients of the nonlinear equation are given as integral expressions.3. The analytical solution of the nonlinear equation was obtained by using the multi-scale method. The amplitude-frequency equation is given, and the relations between the harmonic distortion and nonlinear coefficients are presented. The sound pressure curves of the fundamental, the second harmonic, and the third harmonic were calculated based on a prototype of cone diaphragm.4. The effects of the geometrical and material parameters on the nonlinear coefficients and the displacement patterns been discussed by the method of numerical calculation. The results show that nonlinear harmonic distortion can be decreased by choosing proper geometrical and material parameters of the loudspeaker diaphragm.5. Based on the theory of axisymmetric shells, the characteristics of linear vibration and sound radiation, and the nonlinearities of the exponential shape diaphragm and the parabola diaphragm been discussed.