A thermal control module computes an estimate of a temperature of a speaker, based on an audio signal that is driving the speaker, and computes a gain that is applied to attenuate the audio signal to prevent overheating of the speaker. Thermal control module computes an adapted impedance, being an estimate of the speaker's impedance including its DC resistance, and uses it to compute the temperature estimate. The adapted impedance is obtained from a normal adaptation process when a measured voltage of the speaker is above a threshold, and a decay process when the measured voltage is below the threshold. Other embodiments are also described.