Here's that dynamics article I was talking about
: Soft to Loud: The Nature of Power and Dynamic Headroom
. I think when I initially read it I saw how it was talking a lot about reference level dB scenarios and citing his company's high end speakers in examples, so I didn't know how applicable it was to lower dB situations. Now it makes more sense. An interesting excerpt:
"The problem with many amplifiers and A/V receivers designed for economy (the most watts for the dollar) is that they make the transformer just big enough to produce the voltage output they need [to meet sustained power output measurements into an 8-ohm load], and just big enough capacitors to supply the sustained, continuous voltage and current they need for continuous power, and then the amplifiers quit, so those amplifiers have no real headroom. On top of this, the power may be calculated to be the rated output for one channel at full power and the other five at 1/8 power. So a 100-watt six-channel A/V receiver actually only has 162.5 watts of total power or 27 watts per channel with all channels driven. The better amp builders, who design for performance (reproductive accuracy for the dollar) rather than economy, will install these big transformers with huge capacitors, so then they have all these joules of energy in reserve to produce the dynamics necessary for the music."
Another important factor in dynamic headroom is that the output transistors must be very tough, and there have to be enough of them, to handle these instantaneous high-current conditions, because a great deal of heat is generated very quickly. If the transistors aren't of sufficient quality, they'll be pushed outside of the "SOA" (safe operating area) and fail. And that may happen because there isn't enough heat-sinking to keep the output devices cool under these very dynamic conditions.
One hugely important factor we've ignored so far in this discussion is whether the speakers (and the individual drivers) receiving these 200-watt or 400-watt instantaneous bursts of power from an amplifier capable of 3 dB or more of dynamic headroom can handle the peaks without significant distortion. We already know that the M80ti's are tested up to 1,200 watts of input power, but many speakers when confronted with spikes of power input may suffer something called "dynamic compression."
We've become accustomed to accepting some distortion with our reproduced music, because all amplifier's distortion ratings gradually increase as they approach their output limits or slightly clip the audio signals. When that happens, we turn down the volume because distortion starts to intrude on our listening pleasure, and it sounds "too loud."
This seems to explain why Andrew Robinson was hooking up crazy pro amplifiers to the Tekton Pendragons during testing
, despite their being very sensitive speakers:
I ran two Crown XLS 2000 amplifiers in bridged mono mode to each Pendragon, feeding them a staggering 1,300 watts apiece.
I was going to ask if there were such a thing as an amplifier that didn't output any meaningful distortion at its max output level, but I'm guessing the answer is no, and that the solution is just to get an amplifier that seems extremely overpowered and only turn it up a little.