Amp's nominal power rating - any use?

Amps are rated into resistive loads which says next to nothing about how they do into a reactive real world speaker.

I would propose that amps be rated into 8 and 4 ohm resistors....
Than at the same 2 impedances into +-45 degree reactive loads.

The resultant chart would be a very visual indicator of how the amp does into real loads.

That's the way .....at least on paper to see what an amp can be expected to do.

Magfan,
Your suggestion for measuring speaker output is very much spot on, I wish this would become an industry standard procedure. The current method is of so little real world value in trying to determine an amp`s potential match with a given speaker.

Irvrobinson, no, i never tried the SF with higher power amps. Maybe i should now for curiosity, since due to planning the roll-over to a tube amp, not long ago i got a aprox 100w onkyo receiver for home cinema (with some mordaunt-short speakers) so i have separate systems now for music /movies. I watch cinema a lot and wasn't imagining tiring those delicate 300B with movies...

Kijanki, it is difficult to disagree that music has varying loudness, but 45.9%? I don't think your calculation is nearly accurate enough to claim a number with such precision. For one thing, the dynamic range of music varies so much by music type and recording, though I suppose someone with a SET and minimonitors is unlikely to be listening to Kayne West.

Regardless, I'm still not bought into the efficacy of your calculation.

As for Magfan's comments about adding capacitance or inductance into the power calculation, "next to nothing" seems like a big exaggeration. But considering we're talking about a tube SET here, which is going to be the most sensitive design to load variance, amp and speaker matching is of more importance than usual, I'll agree. Once you're in SET territory, I think the only practical way to tell if an amp is compatible with a speaker is to listen. No one publishes enough specs to make a worthwhile prediction, and even if they did, very few of us could probably do a reasoanble interpretation.

Irv,
I just reread my response and will pretty much stand by it.

Just for an unreal example, a phase angle of 90degrees will result in ZERO power making it to the load. Using the 4foot fluorescent tube next to my workstation as an example, it draws about 1/3 amp. This lamp is consuming about 40va or 32 watts....the power factor is 0.8 and the phase angle is about 37 degrees. The math? PFxVA=Watts.

Tube amps do not like some reactive loads. An 8 watt SET working into a 60degree phase will deliver HALF its rated power to the load. SS is subject to the same limits. But, the amp may not even do that well....half is the upper limit.

I have not seen enough data, but would go out on a limb and say that many amps, even some highly touted ones, won't even do as well as a straight theory calculation (cosine of phase angle x power) says it should.

http://stereophile.com/standloudspeakers/807sonus/index4.html

Stereophile measures of recent version of the SF Guerneri.

Original speaker....from the 90s.

http://stereophile.com/standloudspeakers/487/index5.html