A novel, cost-effective method for loudspeakers parameters measurement under non-linear conditions

The linear model of the dynamic low-frequency loudspeaker is widely used nowadays, and it is well known how to assess its parameters from simple measurements. However, this is a small-signal model which well represents the behavior of a loudspeaker only when slight diaphragm displacements are considered. In many cases it is important to have a more accurate model which takes into account the nonlinear phenomena as well, for example during the development of a feedforward loudspeaker linearization system. It is quite simple to obtain such a model from the small signal one by introducing the dependence of the force factor Bl, the suspension stiffness K_ms and the voice coil inductance L_e from the diaphragm position x. More difficult is to assess these position-dependent parameters. In this paper, novel and low cost methods for the Bl(x) and K_ms(x) identification are proposed. Some experimental result will be presented, and in particular a comparison between the large-signal, low-frequency behavior of the loudspeaker and its model (whose parameters has been estimated with the proposed methods) will be performed. Finally, this model has been employed in order to implement a simple model-based method for the loudspeaker linearization. Other experimental results will be reported and the capability of the method to reduce the second and third harmonic distortion at very low frequencies will be discussed.