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Re: Voltage and Power Paradigms

Ralph,
Thanks for your interest in the workshops we will be holding. I think a couple of them will be relevant to your question. First, we will be doing measurements on amplifiers and in so doing will discuss and speculate on how measurements do or do not correlate to the sound. In the amplifier listening workshop, we will compare the sound of a vacuum tube amplifier with that of a solid state amplifier; because the output impedance of the vacuum tube amplifier is a bit higher, one could argue that it falls closer to what you describe as the constant power paradigm. Finally, we will provide a demonstration of the average and peak power (referred to 8 ohms) levels on well-recorded music playing into a given loudspeaker. Our plan is to display rms average and peak value of average power simultaneously on digital readouts calibrated in watts average power into 8 ohms. This is intended to illustrate the crest factor of the program, and by extension the likelihood of whether one's amplifier is clipping.

Now to the specifics of your question. I have to say that I don't subscribe to so-called constant voltage and constant-power paradigms as you described them. The constant power paradigm is particularly problematic, since with most loudspeakers, if you deliver a truly constant power to the device, its frequency response will be very far from flat. Indeed, if you look at the impedance curve, you will see for many speakers a large rise, sometimes to tens of ohms, at the bass resonant frequency and again at the crossover frequency. Such impedance rises suggest that the true power efficiecy of the loudspeaker is significantly increased at these frequencies. Feeding constant power to the loudspeaker at these frequencies would result in both a voltage rise at the terminals and an SPL rise at the acoustic output. The bottom line is that most speakers are designed for, and voiced for, a constant voltage input (regardless of the power that that happens to correspond to).

I know of no audio power amplifier that produces constant power into a widely varying frequency-dependent speaker input impedance. You may get a little closer to that with an amplifier with a higher output impedance, but still not a lot closer. Closer enough to alter the sound, however. Even the constant current amplifiers that some have proposed are not constant power.

I also don't see stereotyping so-called subjectivistis and objectivists into constant power and constant voltage camps, respectively. This would be similar to categorizing bottleheads as all subjectivists and solid state afficiandos as all objectivists - something that seems wrong to me.

I hope I have addressed your question, and hope you can join us at RMAF for our workshops.

Bob


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