Hi all,
Lots of good advice from JohnK about the relationship of perceived loudness levels and the huge increase in electrical watts required to cause a small subjective increase in loudness.
There is no universal standard for measuring dynamic headroom. When it is quoted or measured, it's in milliseconds (several thousandths of a second) which is sort of relevant, but it's better to try and judge an amp's output capabilities by the robustness of its power supply: How big are the storage capacitors, and the power transformer?
Look through the vent holes on the top for the round capacitors (usually near the transformer). If they're big and fat--the size of a normal soup can (unlikely in all but a few expensive receivers)--and the transfomer is large and heavy, you can assume the receiver's power supply is robust and able to supply sudden demands for output power (an explosion in a HT war move, for example). The capacitors store electrical energy. If they're puny, and an explosion in a movie comes along, the power supply may "sag" and be unable to meet the demands of the output stage, causing distortion.
You can even judge power-supply quality by the physical weight of the receiver (assuming the manufacturer didn't hide a brick inside to trick naive consumers...ha, ha).
It's too complex and long-winded to go into here, but I'm preparing an article on power output standards in multichannel HT receivers. Output for most brands is quoted, at best, in the stereo mode, with only two channels driven. When five channels are driven, the power output often is dramatically reduced, to a fraction of its stereo capabilities. And it's often quoted at just one frequency--1 kHz, rather than over the full frequency range of hearing (20 Hz - 20 kHz). All this is very misleading and confusing for consumers. Standards have sharply declined, partly because manufacturers are trying to jam five or more power amps onto one chassis and sell it at $500 or less while giving the impression that the receiver can output 5 channels at 80 or 100 watts per channel simultaneously. And it can't.
Well, that ought to stir things up....you'll read more when my separate web site, The AudioLofft Report, gets up and running.
Regards,
