Car Subwoofer Amplifier Power Output
There are a few things to keep in mind.

First, the 1 kW figure is almost certainly "peak power", or instantaneous peak power, not rms.

Second, the amplifier is certainly configured as a bridged amplifier, along the lines of 







simulate this circuit &ndash; Schematic created using CircuitLab

with R3 equalling R4 to give a second stage gain of -1. Then the peak-to-peak voltage will be double the voltage from a single amp and a grounded (or, in this case, pseudo-grounded) load.

So, for your nominal 16 volts and 1 ohm, the maximum power will be 1024 watts.