[4] High power audio transducers have a low efficiency, with less than 5% of the amplifier signal turned into sound waves.
A voice coil made of copper wire will have its DC resistance increase by about 72% when heating up from 20 °C (room temperature) to 200 °C, and its sensitivity will decrease by 4.7 decibels.
Or by choosing a transducer other than the voice coil, such as Bruce Thigpen's rotary woofer (1974) or Tom Danley's servo-motor subwoofer (1983).
[6] Power compression is usually considered a long-term problem, arising over time with extended strong signal sent to the loudspeaker.
However, if the change in resistance is short term, observed as heating up and cooling down with each cycle of low frequency waves, then the loudspeaker will increase in total harmonic distortion.