Dynamic Headroom

Kijanki...Agreed that "Unlimited time" would be more than "Continuous" in the definition of power. I don't know how the spec is exactly defined but I think that "continuous" could be 5 seconds or so. This would be long enough to reflect any power supply sag, but not long enough to get into heat sink issues.

Since the average power while playing music is a handfull of watts, but the peak may be hundreds (I have made measurements) I do believe that ability to follow peak voltage is very important. Power supply design is influenced by the need to advertize high "continuous rms power".

Using my MG1.6 speakers playing LOUD I measured average rms voltage in the 5 to 10 volt range but I still saw brief peak voltage corresponding to almost 600 watts. I was using 600 watt amps so I was able to see this voltage.
In the end I decided that while 600 watts for a MG1.6 is not ridiculous, 350 would probably be OK (so I bought CT D200 monoblocks).

Eldartford - I believe standard calls for 5 min rms power. http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=129b71f1c02566f96bb00521fdf0bd03&rgn=d

I remember that amp I used once at New Year's Eve party quit after about 10 min - thermal protection started switching output OFF and ON constantly.

My current amp Rowland 102 is rated 2x200W but Icepower modules inside are rated for 40W continuous and 55W FTC rated power. 150W that my amp outputs with my 6ohm speakers is only 33% louder than FTC rated 55W.

I remember listening to one amp that was very dynamic and had a lot of headroom but on heavy orchestral piece sound just sagged - I suspect that higher momentary power was achieved by higher voltage and power supply caps but when momentary power demand extended to few seconds whole headroom collapsed (small transformer?).

Luxman mentioned by Cerrot was top quality amp imported from Japan until they attempted to sell mass market product thru Costco and lost "image". Competition with cheap brands was not successful while Audio Dealers stopped carrying it. I would expect very good performance and honest ratings from Luxman.

Well....

I would say 101db. sensitive speakers with 1000 wpc.

would qualify as "Dynamic Headroom" as the speakers

only need about 7-10 watts to produce tremendous output.

ALL the rest, is "Headroom" for those transients in both

movies, and music.

Take a 100wpc amplifier that doubles all the way to .5ohms;

That is Dynamic Headroom, at its very Best.

Or another 100wpc amplifier, that produces 140wpc.@4ohms,

and maybe 150wpc. @2ohms very briefly.

The second amp. does NOT have ANY Dynamic Headroom.

This is why, not ALL 100watt amplifiers are the same; Nor

ANY others for that matter.

"Parts is parts"

Junk is, well...worthless.

Wonder why Loudspeaker Makers, went from "low impedance"

speakers in the 80's and 90's, but are now making much

MORE accurate speakers, that are not 86db. @4ohms; But

95-97 db. @8ohms!

Because they want MORE output, without needing an

"arc-welder", type amplifier.

There is NO such thing as "too MUCH Power!"

One does not typically listen to music with the volume

set to the "Maximum?"

Only enough to fill the room evenly with sound.

That is why I implement multiple amplifiers, so that

"Headroom" is NEVER an issue.

I Love MUSIC!

Kijanki...So it seems that the FTC power spec IS supposed to cover thermal considerations. That might be very reasonable for pro amps which play highly compressed and peak limited music at maximum volume. I play music on my system very loudly (but not compressed music) and my digital amps get barely warm. My comments above are aimed at home audio amps.

Eldartford - I don't listen very loud, perhaps 50% of max what makes already 1/10 of the power and because music does not contain peaks alone but most likely less than 50% volume most of the time it is another 1/10 of power. Music has also gaps - it is not continuous sinewave making it even less. I would assume that average power delivered to speakers is less than 1% of the max rms (around 1.5W).

Output stage of my amp is supplied from regulated 47V making 370W peak at 6 ohm. It's peak and not rms so overall headroom is not very big but it sounds big. It might be because of immediacy of response but also because of my moderate listening levels.