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SET Asylum Single Ended Triodes (SETs), the ultimate tube lovers dream. |
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In Reply to: RE: Drawing the line posted by dave slagle on September 21, 2015 at 07:53:54:
"I have another friend Johannes who could nail the relative phase of a SE amp to a speaker. This doesn't have anything to do with absolute phase but rather the idea that air is harder to compress than it is to rarify which sets up a situation to create an even order distortion. When you combine this even order distortion generator with another (a SE tube output stage) suddenly you get very different distortion spectra based on phase. Johannes would simply instruct me to listen to the bass and it was easy to hear."
This is an interesting point, since indeed there must be some degree of asymmetry in a sound wave, since air pressures can increase arbitrarily high, but they cannot decrease below zero. On the other hand, as I learned from a Wiki page, a sound level of 94dB corresponds to a fluctuation of about 1 part in 100,000 around atmospheric pressure, so one would have thought any non-linearities associated with this effect would be really tiny; at something like the 0.001% level or so. This looks as if it could be rather negligible in comparison to the order of magnitude of distortions from the amplifier, and from the speaker itself.
In fact, I think I have seen astonishingly large distortion figures quoted for loudspeakers. Isn't it possible that, if there is some audible effect associated with the phase choice for the connection of the amplifier to the speaker, it is much more likely to be associated with asymmetries in the way the loudspeaker itself responds to being driven outwards, as opposed to being driven inwards? I would have thought that such kinds of mechanical asymmetries in the behaviour of the loudspeaker cone would be overwhelmingly more important than non-linearities in the way the acoustic wave propagates in the air.
I was a bit puzzled by you final remark: "important thing to note for all you absolute phase junkies is simply swappping speaker cables polarity is not a fair way to reverse phase". Until I reached that point in your message, I thought that you precisely were talking about what happens if you reverse the two speaker wires? What did you mean, if not that?
Just to make sure we don't go off on a complete tangent, this discussion has absolutely nothing to do with the discussion of the phase of one speaker relative to the other in a stereo system! The effect you are wanting to talk about is, I believe, what is normally called "absolute phase," and could be discussed purely in a mono audio system. It is concerned with the issue of whether a transient attack at the beginning of an impulsive sound will drive the speaker cone forwards, towards the listener, or instead drive the cone backwards, away from the listener. This effect would precisely be reversed if one switched over the two wires going to the speaker. Thus I am puzzled by your sentence apparently saying that that is not what you were talking about.
Anyway, in summary, I could believe that absolute phase has a chance to be an audible phenomenon, because of non-linearities and asymmetries in the system. But I would have thought non-linearities and asymmetries in the mechanical response of the speaker cone would be far more likely to be at play here than non-linearities in the propagation of sound waves in air.
Chris
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Follow Ups
- RE: Drawing the line - cpotl 09:04:08 09/21/15 (4)
- RE: Drawing the line - dave slagle 09:26:44 09/21/15 (3)
- RE: Drawing the line - cpotl 09:41:29 09/21/15 (2)
- RE: Drawing the line - dave slagle 09:52:16 09/21/15 (1)
- RE: Drawing the line - cpotl 11:20:43 09/21/15 (0)
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