Some of you may know of PS Audio Paul McGowan's daily missives about various audio topics. He has been writing recently about amplifier power supplies [an excellent long series breaking down the relative merits of linear and switching power supplies], leading in to his recent topic about amplifier power. Today's post, titled Music Math, is especially interesting, because it summarizes the math about amplifier power reproduction of sine waves, spoken language, and music:

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And then Paul turns to the natural question that any of us on this forum might ask:

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Looking forward to reading that tomorrow.

It should surprise no one that PS Audio is working on an all-new series of switching amos, and so these posts serve a commercial purpose, but they are interesting and I commend them to anyone who might find the topics enjoyable.

Very interesting.  Being new to the low watt club I am excited to try some hi eff speakers and maybe play with some OB types

"Many of you are asking me if all this is true, which it is, how come my little 10 watt SET amplifier works just fine on my speakers?  Are tubes so much better at peaks than solid state that I am getting away with something?"

DBC's quotes from Steve's paper on the first watt are on target.

Think about the music envelope, the range of signal that you're amplifying, from the most subtle low level information to the peaks.  

SET amps are inherently genuine class A, and as such excel at very low level detail resolution.  The small details and ambient cues from the recording are all down at these levels, and SET's expose them in a manner on par with the best performing amps regardless of cost.  Compare and contrast to standard ss class A/B, where their low level detail resolving ability is masked due to crossover distortion or the feedback required to combat it-you always have to turn such systems up a bit for them to come to life just to overcome their low level detail resolving deficiencies.

But there is some trickery going on at the other end, the signal peaks, and in this case I think us SET users indeed are "getting away with something" mischevious.  As  these amps (I refer strictly to the SE84C+, as that's what I own) start to clip, the distortion profile is a low order, monotonically decaying pattern (meaning both even and odd harmonics, of low order and rapidly diminishing levels as the order goes up).  Under these peak power circumstances the amps electrical output plateaus, but he harmonic distortion content increases, and the "trick" is that we perceive this as increased loudness.  In this sense, a SET acts as an ideal compressor when pushed into clipping-at least up to a point.  Fortunately, SETs have a ton of wiggle room and can exhibit large amounts of THD before they sound objectionable.  Compare and contrast to ss power at clipping: predominantly odd order harmonics that extend much much higher, which is pretty much unlistenable even in minute amounts.

So what we get is excellent detail resolution at the low end, and ear friendly compression at the top end.  I think this is why SETs at 85 decibels sound as loud as ss amps at 95 decibels.  Throw in some speakers that are sensitive enough to dwell in the first couple watts, and you have a recipe for musical enchantment.  

I'll be curious to see what Mr. McGowan has to say tomorrow.

The folks pouring 500 watts into their speakers should buy stock in Phonak (they make hearing aids).  What goes around comes around.

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I think this is why SETs at 85 decibels sound as loud as ss amps at 95 decibels.

I have not had that experience. To me, volume matching is pretty much just that. However, at the same volume, especially a slightly lower one, I find our low-wattage amps much more engaging.

Yes, that particular statement may be an exaggeration, but yes, more engaging is exactly what I'm talking about.  More low level detail, more meat on the bones.  Level matched, the SETs win the pepsi challenge every time.

Yes thanks.
I`ve allways had one of those little personal chessnuts in that volume isn`t allways equal to loudness...more like headroom. An increase in volume does just that, expands the space that the music inhabits, or makes it grow. Yes it does sound louder, but can you make it louder without expanding the volume ? Perhaps amps have a `sweet spot` so thats how you decide which power model is best for your requirements.

Should be an interesting series of articles.

I'm not sure I'd say "never." There are many low powered amp users with much higher efficiency speakers than yours (and mine) that report great dynamic contrast and strong rhythmic drive.

Also preamplification and format can matter.

Nobody is wrong in their desire to listen to their studied preferences, as long as it get's them grooving to their music collection.
                                   

Paul's Post today, titled Tambourines, hits the SET topic head-on. Note that Paul himself does not render this indictment, but he quotes a fellow who does:

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This then leads McGowan to these calculations, which he acknopwledges are fairly extreme:
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Hmmm. Let the fireworks begin. No argument that the numbers produce these results, but it sure doesn't seem to be what my ears hear. May be time to get out the SPL meter and computer.