Frequency Dependence of Damping and Compliance in Loudspeaker Suspensions

The viscoelastic effects in loudspeaker suspensions are investigated from a theoretical point of view as well as via measurements of the electrical impedance and velocity for two loudspeakers, one with high-loss, the other with low-loss surround. As the viscoelastic effects lead to frequency dependence of damping and compliance, better parameter estimates can be obtained with a loudspeaker model that includes these effects. For example, underestimating the mass associated with the added-mass method can be avoided if the frequency dependence of the compliance is included. Here the study is limited to the audio frequency range. Therefore the relative changes in compliance are quite small, and independent of these the loudspeaker parameters can be derived by using a measuring technique, which is evaluated. However, viscoelastic damping may appear and is inversely proportional to frequency. Therefore a simplified model is proposed which includes only frequency-dependent damping. This model is shown to give a very good fit with regard to both electrical impedance and velocity response.