A Study On Sound Absorption Structures Based On Shunted Loudspeakers

In this thesis, the sound absorption performance of shunted loudspeaker is investigated. Two composite structures based on the shunted loudspeaker are proposed for broad band noise and harmonic noise absorption. The contribution of the shunt circuits to the sound absorption performance is discussed.Previous studies of the shunted loudspeaker are introduced first. Then the sound absorption formula of the shunted loudspeaker absorber is derived. The effects of the parameters of the shunted loudspeaker absorber on the absorption coefficient are investigated. It is shown that, the resonant frequency of the absorber can be tuned by adjusting the capacitance and inductance in the shunt circuit and the volume of the speaker box. The sound absorption coefficients at the resonant frequency can be tuned by changing the resistance in the shunt circuit.A composite sound absorber composed by a micro-perforated plate and a shunted loudspeaker is proposed for broad band noise absorption. The absorption formula is derived for the composite absorber using the electrical-mechanical-acoustic analogy analysis method. It is found that the sound absorption performance at low frequencies can be improved by adjusting the parameters of the shunted loudspeaker, while the sound absorption characteristic at the middle and high frequencies is mainly determined by the micro-perforated panel.Finally a double resonant absorption structure based on the shunted loudspeaker is proposed. Negative resistance, positive capacitance and inductance are chosen as the shunt circuit to generate high absorption coefficients at two certain frequencies. It is efficient to control the noise with several single frequencies, for example the transformer noise.