The Grim Reality of Speaker Efficiency
A direct-radiator moving-coil loudspeaker is one of the most mechanically inefficient devices in modern technology. A typical high-power subwoofer or PA driver has an electro-acoustic efficiency of only 1% to 3%. This means that when you pump 1,000 Watts from an amplifier into a subwoofer, 970 to 990 Watts are converted directly into pure thermal heat inside a voice coil no larger than a soda can!
The Thermal Compression Mechanism
As the copper or aluminum voice coil wire heats up from ambient (20°C) to 180°C - 220°C, its electrical resistivity rises in direct proportion to its Temperature Coefficient of Resistance ((alpha approx 0.00393)):
Power Compression (dB) = 10 × log10( R_hot / R_cold )
A nominal 8-Ohm subwoofer with a cold resistance of (R_e = 5.6,Omega) will see its resistance climb to over (9.5,Omega) under heavy drive! Because modern solid-state amplifiers deliver constant output voltage, the increased resistance throttles current draw, causing a 2 dB to 4.5 dB drop in acoustic volume.
The Law of Diminishing Returns
When thermal compression reaches 3 dB, half of your amplifier power is being wasted. Doubling your amplifier from 1,000 Watts to 2,000 Watts will not make the bass noticeably louder; it will simply heat the voice coil faster until the high-temperature epoxy binder carbonizes, resulting in a catastrophic voice coil short.