1. A method of controlling a loudspeaker output, comprising: modeling a frequency-dependent input-voltage-to-excursion transfer function of a loudspeaker, by: for a plurality of measurement frequencies, measuring a voltage and a current and deriving an impedance at the measurement frequency, and from the plurality of impedance values deriving a frequency-dependent impedance function; one of estimating, measuring and obtaining the blocked electrical impedance and a force factor for the loudspeaker; calculating the frequency-dependent input-voltage-to-excursion transfer function from the impedance function, blocked electrical impedance and force factor; and using the frequency-dependent input-voltage-to-excursion transfer function to control audio processing for the loudspeaker.