Patent ID: 8259953

Claim:
A method for protecting an electro dynamic transducer against thermal overload of a voice coil provided in the transducer, comprising: detecting a current through the voice coil, estimating a resistive part of a voice coil impedance, based on the detected current, and attenuating an output power supplied to the transducer based on said estimated resistive part of the voice coil impedance, wherein the estimation of the resistive part of the transducer impedance includes: creating a set of sample pairs of detected values of current through the transducer voice coil and voltage across the transducer voice coil, defining a model of the transducer, said model being a discrete time difference equation describing a relationship between voltage and current in the transducer, in which the resistive part of the impedance is an explicit parameter, rearranging the discrete time difference equation to isolate the resistive part of the impedance, calculating the resistive part of the impedance based on said set of sample pairs of detected values and said model of the transducer, and low pass filtering the calculated value of the resistive part of the impedance.