Dynamic Headroom

Cyclonicman - Thank you for you valuable summary.

Thanks for all the comments. Feel free to battle it out. Interesting conversation

Kijanki...The 47 volts you cite is DC. Allowing for a 3 volt drop through the output transistors this suggests that the amp can swing +/- 44 volts. But that 44 volts is the peak of the signal. For a sine wave signal this would allow 228 watts RMS.

Almarg...We agree. My point is that an amp which is current-limited for high voltage output is a logical design for signals that have huge peak-to-average ratios (like music). Having current to spare is no help if you can't swing the voltage. We use amps with huge power specs because that assures the voltage swing. Having that swing continuously is not really necessary.

Edartford - It is class D amp with full H-bridged Mosfets. There is practically no voltage drop on them (possibly a volt total).

As for amps being design for "huge peak-to-average" - that's true but this average might vary. Some amps will handle Jazz nicely but give up at heavy orchestral piece (much higher average).

Also note that headroom is not necessarily "how much punch is available above maximum rated power". No one (virtually) listens at maximum rated power anyway (well perhaps a few have done so, but speaking realistically it is not an acceptable practice).
Anyway: your *available* headroom is the difference between the actual power level at which you're listening to, compared to the maximum available peak.

20dB, or more, is considered optimal headroom.
10dB is 10 times the power; 20dB is 100 times the power. So if you're listening at 2 watts then you need 200 watts available if you want that 20dB of headroom.

My rig is setup so that it virtually never clips. With high effeciency speakers (105dB SPL @1 watt 1 meter) if I'm listening at 2 watts per channel it's already quite uncomfortably loud for most people. So you need a decent sized amp and high efficiency speakers to stay 100% of out clip.