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In Reply to: RE: Drawing the line posted by cpotl on September 21, 2015 at 09:04:08
By absolute phase I indeed meant swapping polarity of both channels at the same time and not one channel in relation to the other.
The air thing was under the assumption of mainly bass (due to the large amounts of air movement) and an asymmetrical design (not an open baffle) where there is a pressure build up in a back chamber. I was using lowthers in rear loaded horn at the time.
dave
Follow Ups:
"By absolute phase I indeed meant swapping polarity of both channels at the same time and not one channel in relation to the other."
OK, good...we are on the same wavelength (so to speak)!
I think, though, that the percentage change in air pressure around the quiescent 1 atmosphere is still absolutely tiny, even for loud low-frequency sounds.
But the asymmetry of the loudspeaker response, together with the asymmetry of the SET amplifier response (because of its predominant 2nd harmonic distortion) would certainly, I imagine, lead to the possibility of either addition, or subtraction, of the two asymmetries, depending on the polarity of the connection to the speaker. I'd put my money on that, rather than asymmetry in the acoustic propagation of the air wave itself.
Chris
It was presented to me as the non-linearity of air as being the cause. What other aspect of a speaker design could generate even distortion?
A slightly off center voice coil in the gap?
suspension / spider?
dave
"It was presented to me as the non-linearity of air as being the cause. What other aspect of a speaker design could generate even distortion?
A slightly off center voice coil in the gap? suspension / spider?"
Quite possibly.
I tried quickly googling around a bit, and distortion figures for loudspeakers seem to be commonly up to the order of several percent, especially at low frequencies (presumably because the amplitude of the cone movement gets larger at low frequencies). These distortions include substantial second harmonic, which implies asymmetry.
So if the second harmonic distortion of the speaker were comparable with the second harmonic distortion of the amplifier, then I suppose there could be a significant and audible difference if the two asymmetries were combining on the one hand in unison, versus on the other hand in opposition.
By contrast, I think the non-linearities in the acoustic propagation in air will be way down, for any kind of realistic sound pressure level. (The "maximum possible" sound level in air at standard ambient pressure, based on supposing the pressure reaches down to zero in the troughs, is about 194 dB. which is pretty loud!!!. A loudspeaker, on the other hand, will be hitting one or other of its end-of-range mechanical movement limitations at hugely lower sound levels. Thus asymmetries at normal listening levels will be likely to be much bigger for speakers than for air, since the ratio of typical cone movement over maximum possible cone movement is a much bigger fraction than the ratio of air pressure change over ambient air pressure.)
Chris
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