5 minutes is the FCC's idea of continuous (which I think is a little long for an indoor application) but it is what it is.Car and truck engines have mixed results when used in aviation and marine applications. Most were never designed to produce their max rated power continuously. The typical car engine uses only about 1/4 of its rated power continuously when cruising down the freeway and its full rated power only for brief moments. Most car engines don't last when installed in boats & airplanes that continuously demand 70% or more of rated power. Even when driven at SCCA and similar racing events, many of these engines get heat soaked and lose power or go into "limp mode" if operated at full power in low gears for more than a few minutes. A few car engines have worked well in marine & aviation applications; they are either modified or comprise the over-engineered exceptions that prove the contrary rule. For each one, there are many others that don't.
This analogy to engines is not ideal because of the term "continuous". Most car engines will produce their rated power (for example on a dyno) when properly maintained - yet are not certified or advertised to produce that max rated power continuously. Yet when it comes to audio amplifiers, the term "continuous power" is used, even if the amp shuts down or melts while producing that power. It's understandable if that is misleading.
On the other hand, I can't see owning anything less than a 100 watt (at 8 ohms) rated amp (in spite of the fact that I do own 2 NAD 2100's
[but they will put out much more than their rated 50 watts at 8 ohms]):
Specification
Stereo Mode
Continuous Average Power Output into
8 ohm (Min, RMS power per channel
20-20kHz both Channels Driven
with no more than rated distortion) .......: 50 W
Rated Distortion 20Hz-20kHz ...............: 0.03%
Clipping Power (Maximum continuous....: 70 W
power per channel)
IHF Dynamic Headroom at 8 ohm .........: +6dB
IHF Dynamic Power at 8 ohm ...............: 200 W
(Short term power) at 4 ohm ...............: 250 W
at 2 ohm ...............: 330 W
Damping Factor at 50 Hz (Ref. 8 ohm) ..: 100
THD 20Hz-20kHz from 250mW to rated : <0.03%
Frequency Response, Lab input ...........: 3Hz - 100kHz, +0db -3dB
Signal to Noise Ratio A-weighted .........: 100db ref 1W, 117dB at rated power
Bridged (Monophonic) Mode
Continuous Average Power Output into
8 ohm (Min, RMS power per channel
20-20kHz both Channels Driven
with no more than rated distortion) ......: 150 W
IHF Dynamic Headroom at 8 ohm .........: +6dB
IHF Dynamic Power at 8 ohm (max.......: 500 W
(Short term power) at 4 ohm ...............: 660 W
So they are great in a bridged mono setup for 1 per channel.
In my case, I tri-amp my NAD 2200's: 2 bridged mono at 4 ohms, 1 for each channel and one running at 4 ohms in stereo for my pair of subs.
When I go put in my yard, with my windows open, I am probably running 40-50 watts per amp, continuous.
So, at max power, even for 5 minutes, would be unreasonable.
If I was doing the same thing off of one amp...don't know???