Multiple Degree Of Freedom Structure In Loudspeakers

Most loudspeaker analysis is based on a simple oscillator structure.It is a single degree of freedom(SDOF)structure,including a moving mass,a spring and a damping.Usually the electro-mechano-acoustical analogous circuit method is used to build a lumped parameter model for analysis.T-S parameters,as a most commonly used parametric expression method to describe electro-dynamic loudspeakers,is based on this SDOF structure.But in practical cases,the SDOF structure is an ideal model,the real model may have some differences.Multiple degree of freedom(MDOF)structure needs to be analyzed.For some kinds of loudspeakers,such as panel loudspeaker,vibration loudspeaker,piezoelectric loudspeaker and etc.,there exists a pair of masses driven by the interaction forces between them.In a panel loudspeaker,the panel and the exciter interact with each other.In a vibration loudspeaker,the powered voice coil and the magnet interact with each other.In a piezoelectric loudspeaker,the inner part and the outer part interact with each other,which generate a bending moving pattern.They all have an internal excitation 2 degree of freedom(IE2DOF)structure.Analogous circuit method is used to build a lumped parameter model to analyze its dynamic behavior.The calculation shows that the IE2DOF structure have a frequency response of two resonances and one anti-resonance.The resonant and anti-resonant frequencies are given.Then a piratical measurement is carried out,which shows s good agreement with the previous calculation.In a normal moving coil loudspeaker,which is regard as a SDOF system,MDOF structure also exists.The compliance of the diaphragm,the mass of the suspension and the mass and compliance of the air near the diaphragm all generate a MDOF structure.In the 3 conditions,analogous circuit method is used to build a model to study its dynamic behavior.According to practical situation,different kinds of MDOF structures are analyzed in the research.Electro-mechano-acoustical analogous circuit method is used to build a lumped parameter model for analysis.The research shows that the MDOF structures in loudspeakers result in additional resonance and anti-resonance.This research is of great significance to the practical application in loudspeaker modeling,simulation and analysis.