Originally Posted by darthray
While I am not sure. The way I read his post, you would need two 20 amp circuits for dual subs.
That said, I could be completely be on left field on this one
Typical usage will easily allow operation of 4 SubMersive HP units on a single, dedicated 20A breaker. By this I mean a system with 2xHP+ amplified units with each driving an HP-Slave unit; 4 cabinets total, 8 x 15" woofers, and actually a rather common configuration our customers arrive at directly or through a couple upgrades.
Circuit breakers have a duration related behavior. This is rather useful in homes as it might otherwise be tricky to get garbage disposals to initially turn on, or toasters to not trip breakers when turned on. Ultimately the intended job of a circuit breaker is to keep over current conditions from overheating wires in the power system, and to interrupt fault conditions (ie hot shorted to neutral or other). Wires don't heat up instantly, so immediate, brick wall protection has no benefit.
Standard household breakers can pass 1.5-10x their trip current for short a duration. The shorter the duration, the more it can pass. Considering it's dissipated power which heats things up, this makes sense, as power requires duration, as a Voltage burst 2x longer but the same intensity results in 2x the power dissipated.
Common figures used for power requirements use 1/3rd to 1/6th draw from rated audio power, particularly if we exclude subwoofers. If we were only powering signals above 1kHz in an active system, we might load up to 1/6-1/20th the power draw from the rated audio power. For subwoofers that can range from 1/4 to as much as 1/2 rated power if pushed hard into limiters, other protections, or hard clipping.
Of course the amplifier type has to be considered, as class AB amplifiers are much less efficient, and plenty of class D amplifiers are 70-80% efficient, while the 4000W amplifier I use is closer to 90% efficiency. As an example, a 2000W amplifier that is 50% efficient could draw a maximum of 4000W, while an 80% efficient equivalent could draw a maximum of 2500W, while a 90% efficient amplifier could draw a maximum of ~2220W.