Interesting, I've been wondering and inquiring about these amps LF/ULF aptitude since they hit the scene.
This is the way amps are suposed to behave when asked to deliver beyond their means.....unlike others that burn up.
IMO, designing a sytem operational with 2ohm sub loads on amplifier channels is, at best, less than optimal. At worse, a bad idea.
Those mentioning the 2ohm nominal component to this issue are dead on,...as there's likely points on the complex Nyquist whereby the loads dip further down, approaching a dead short.
To properly determine voltage, you must check line voltage under load,...coinciding with demand. Wih minimal load, you're just going to see whatever your service sees.
Don't these amps have some type of voltage correction imunity? If so, they prolly won't behave linearly at the current limits (with a nice predictable roll-off). They'll pump along, relatively immune to line voltage, then suddenly there's nothing left, and the circuit opens protectively. Just speculating.
On a related note;
Subwoofer amps work best on circuits optimzed for such use. Yes, the 20a breaker can pass up to 50-60 amps for perhaps the duration of the scene. Easily up to 40amps for a full 30 seconds! The problem exists in the branch cuircuit sizing, and instantaneous voltage drop. Up-size the wiring for subwoofer circuits. Rarely is there such an effective single step upgrade, with such a significant potential to eliminate a system chokepoint. YMMV on PS caps, the freq of the effect, the duration of the effect, etc, and these high speed PS configs need as much stiff voltage as possible.
Best of luck Stereodude, interesting findings.