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How much power do you need?

Posted by PaulF70 (A) on September 9, 2016 at 17:25:09

In an article about tubes vs. transistors, Roger Sanders defends the thesis that speakers actually need LOTS of power - much more power than people think - and, thus, solid-state amps are the way to go.

Roger's a smart guy (I had dinner with him once, about ten years ago), and his stuff sounds good. It's not really my cup of tea for the most part, but in general HiFi terms, it sounds good. Better than quite a lot of gear, overall.

In the article, he challenges readers to put a 'scope on their speakers and see what kind of power they're sucking, and how much they're clipping. He asserts that for most people, the amps are clipping a lot.

He also asserts (rather arbitrarily, it seems) that typical direct-radiator speakers of ~90 dB/W or so require about 500W of power to avoid clipping regularly.

My own Beauhorn speakers are approximately 104 dB/W (measured at 103.5 dB/W/m by the illustrious Thorsten). According to Sanders' formula, I'd thus require about 20W to avoid clipping.

So, I got the 'scope out, and connected to the terminals of my Welborne DRD 45 SET amps, which produce about 1.5W of power going downhill. I then proceeded to play music - loudly. One example is the track "Black Magic Woman" on Pat Barber's "Companion," which has an extended drum solo that is quite something. I played this track with peaks of 92-94 dB at the listening seat in my large room, 10' from the speakers' fronts, according to the Rat Shack meter which is not fast enough to accurately report true SPL peaks (they were likely 3-6 dB louder). Mind you, this is *loud*. If you listen more loudly than this regularly, for long periods, you are damaging your hearing (unless it's already damaged).

Well, I never saw clipping on the 'scope. Not at all. Not on that drum solo or other music. It just was not happening. Sure, Class A tube amps clip softly, but:

1) I didn't even see that
2) This actually destroys much of Roger's argument, incidentally

And, as for experimentation bias, frankly, I kind of wanted to see clipping, so I could have an excuse to buy those gorgeous Thoress 845 monos on audiogon. Oh man they look sweet.

Looking at the numbers, I am not surprised. At 104 dB/W, we're going to get around 94 dB at 10' with one watt of power - but that's totally neglecting room gain and the second-speaker contribution (much signal is shared, of course). So, it is not surprising that 1.5W amps can play these speakers more loudly than people ought to be listening without clipping.

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