Study and characterization of odd and even nonlinearities in electrodynamic loudspeakers

In acoustic echo cancellation (AEC) applications, often times an acoustic path from a loudspeaker to a microphone is estimated by means of a linear adaptive filter. However, loudspeakers introduce nonlinear distortions which may strongly degrade the adaptive filter performance, thus nonlinear filters have to be considered. In this paper, measurements of three types of loudspeakers are conducted to detect, quantify and qualify nonlinearities by means of periodic random-phase multisines. It is shown that odd nonlinearities are more predominant than even nonlinearities over the entire frequency range. The aim of this paper is then to demonstrate that third-order (cubic) adaptive filters have to be used, which is in clear conflict with the extensive, almost unique, use of second-order (quadratic) Volterra filters.