The power to SPL calculation is pretty much aligned with engineering understanding. Yet reality does not seem to support this kind of calculation. For example if we can all agree that 2W is all needed to produce 78 dB at 3m away, then adding extra cushion by a factor of 5 even (to bring the power requirement to 10W) is not bad an engineering cushion, really, to account for dynamic peak or other Murphy's law situations. Yet in reality, would we buy a 10W/channel amplifier to drive anything? Even a factor of 10, bringing the wattage to 20W/channel is a no-no.
I like the idea of using the needle movement on Pass equipment to tell when the amp. moves out of class A. My speakers has a 4-ohm impedance, meaning 120W/channel drawn from the XA60.5. The needle vibrates ever so slightly around 100 dB when my ears were about to burst because I accidentally set the volume too high. The vibration is very light, as the needle likes to lean back to its static position around 12 o-clock when the dynamic peak is gone.
I like the idea of using the needle movement on Pass equipment to tell when the amp. moves out of class A. My speakers has a 4-ohm impedance, meaning 120W/channel drawn from the XA60.5. The needle vibrates ever so slightly around 100 dB when my ears were about to burst because I accidentally set the volume too high. The vibration is very light, as the needle likes to lean back to its static position around 12 o-clock when the dynamic peak is gone.