Axiom Home Page Forums General Discussion Home Theater How much power do I need - m60 measurements

Good test for volume level's, I don't think anyone would disagree that more power louder sound. But as Alan wrote
"Specifications (distortion, noise, etc.) of preamp-processors and power amps are usually a bit superior to an A/V receiver, since there is better internal physical separation of wiring pathways (more room), hence less chance of interference (and resulting noise) from nearby hum-causing component parts."
Can that be measured?

And I thought I was good at math.

Oh no, and female JohnK

Very good, Gena. Keep in mind that in addition to the direct sound, which falls off at a rate of 6dB per doubling of distance, assuming omnidirectional dispersion as a sphere(the area of the surface of the sphere being 4pi[r(squared)],doubling the radius quadruples the area, leading to a SPL 6dB lower), the reverberant sound must also be taken into account. See this analysis , especially fig.10.4.1, for an application of combined direct and reverberent sound. Linkwitz also has an excellent discussion of room acoustics on his site . The information found by scrolling down to "Reverberation distance" and "Amplifier Power to Obtain Reference Level" is particularly in point. At the "critical distance"(aka "reverberation distance"), which is about 3-4' in typical home listening rooms, the reverberant sound is equal to the direct sound and the combined level is therefore 3dB higher. At longer distances, as the direct sound falls off, the reverberant sound remains relatively constant at the critical distance level in typical home listening rooms.

This may seem somewhat technical, but the practical effect is that far less power is used than is sometimes assumed if the combined sound fields aren't taken into account.

"Specifications (distortion, noise, etc.) of preamp-processors and power amps are usually a bit superior to an A/V receiver

Good point and if I start from scratch it would make sense. However, many people think about adding an amp to already existing receiver. Even it's a very good amp it sill has distortions that will be added to whatever the receiver has. So one can end up it with the power that only a very small fraction is used AND more distortions.

Good point John.

I am not an acoustic specialist, so I thought it was loosely called the room gain.

You don't think it would grossly change the result, do you?

Thanks for the info,

Gena

You must be ambi ...

Yes, it's called bi amping

I'm picturing you in a white lab coat and a clipboard doing all these experiments

Well, this what I do. Sort of. Sans the lab coat

I do have to say Gena, I am very impressed with your knowledge, you have probably forgotten more than I'll ever know about this stuff

Michael, of course lower noise and distortion levels are measurable and are made part of a unit's specs. The point is, however, that once these levels are inaudible to humans, reducing them still further(either in a different receiver or a separate amplifier), while showing good engineering, results in no audible benefit(note of course that Alan doesn't say that it does, and his past posts show that he certainly isn't into amplifier "sound").

Only carefully controlled blind listening tests can accurately examine these factors. The classic amplifier listening tests from Stereo Review , which enraged some audiophiles(but opened the eyes and ears of others who were able to get their heads up out of the sand)illustrate the unreliability of open listening. Differences which were lavishly described before the blind tests began disappeared once the name plates and price tags also disappeared. Among the notable results was that the $12,000 pair of tube amplifiers(correctly designed without a flawed "tube sound")were indistinguishable from the $220 Pioneer receiver. So, we can't follow the old "Just trust your ears" mantra unless we make sure that we aren't allowing other influences to mislead us.

Excellent analysis, Gena. Thanks so much for taking the time to document your experience.