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[ 1) If signal velocities of the signal is frequency dependent, then wavelength is no longer inversely rated to frequency. At least, the direct formula is a linear simplification of the actual relationship. I'm worried about the probable impending consequences of this statement, for it's a basic rule at the heart of most electronics. ] Have no fear, there is no violation of the laws of physics. First, think of waves traveling in different mediums, the speed of transversal is different for different mediums. As an EM wave travels through the plastic of an insulator (dielectric), it is slowed due to the dielectric constant of the insulator, and in some cases, such as for PVC, the dielectric constant is NOT constant with frequency {actually, the dielectric constant is more correctly called the dielectric coefficient}. Differing plastics would cause diferent rates of travel. Just as light bends as it enters the water from the air, there will be dispersions, refractions, etc. as an EM wave travels through different media. As to the case for conductors, one must realize that a case could be made for ordinary copper and silver to be considered as degenerate cases of a perfect conductor. A perfect conductor will not allow ANY penetration of an EM field, the E-field would be completely and totally shorted out (in this regard, real world conductors are closer to perfection), while the magnetic field would be totally repelled by equal but opposite surface currents that did not penetrate into the conductor. The only reason even the magnetic field penetrates into the real world conductor is that it is not conductive enough to provide a perfect expression of the Messnier effect. Just some food for thought, and as such, represents my own imperfect understanding of the actual mechanisms, as trasnlated into layman's terms. [ 2) In your average round 26 gauge wire, all things being equal (assuming a continuum), what's the effective area.vs.frequency (as LFs retract from the surface & HFs migrate to the surface both using less of the physically available wire)? ] It helps to keep in mind that the skin depth of a conductor is NOT absolute, that is the very definition of the skin depth is the point where the current flow is down to 37% of the total, hence, there is a continuous change between the current density at the surface, and the current density toward the center. In copper, the skin depth is commonly refered to at 20 kHz as 0.463 mm, and many take this to mean that if you have a 20 gauge wire, with a typical diameter of 0.813 mm, and less than twice this skin depth, that there will be no difference for the current flow for the highs and lows. Obviously, if the skin depth is not absolute, and the depth only refers to a relevant point on the curve of current reduction, then this is a false and misleading concept. Hence, for a 26 gauge wire, the current flow in the center at 20 Khz will be down to roughly 2/3 that of the surface. While the net effect in terms of ONLY total resistance of the wire at 20 Hz, vs, 20 kHz is not that great, I think the fact that the current is still being pushed out toward the surface, even in such a small wire, is significant. It obviouisly means that surface conditions for the wire are important in terms of cyrstaline integrity, freedom from contaminants, including silver plating. [ 3) I've found it interesting while measuring tweeters that the skin-effect reduction of used VC wire disguises itself well with the inductance of the "Le" driver, since the resistance increases much like
inductance behaves. However, the real portion of impedence drops the current so the subsequent effective inductance drops too. With your cable experience & measuring equipment you may find this phenomenon interesting too. FWIW, the phase seems to behave assymptoticly to about 45-degrees (rather than the expected 90) among the better tweeters that I bothered measuring. ] Are you sure it is the skin effect that is causing the inductive behavior, or the more likely and ordinary self-inductance of the coil of wire that is the voice coil? Tweeters have several factors that cause the behavior of the drive unit as a whole to deviate from pur inductive behavior, including motional impedance effects, resonances, etc. [ 4) Does the actual signal travel inside group velocity envelopes where voice can be distorted by its composite Fourier frequencies travel at independent speeds? Thus, the signal reconstruction may defacto phase the vocal components forever loosing the character of the signal. ] While there may be a phase shift effect as you traverse the audio spectrum, the amount is going to be very small due to typical LCR values. Now for some cables, where the designer uses atypical LCR values to optimize for one aspect, and then uses a compensating network to bring the total impedance (and possibly the phase shift) back under control, the amount of phase shift that the uncompensated cable might have would be much higher, and the network then has a profound effect on the end result. However, the total sum of the cable and network is what you would comapre to another cable, and it being less than totally perfect in this single regard may be overshadowed by the other factor that were optimized for in that particular design. ----------------SIGNAL
[ 5) Why would conductor penetration into the metallurgicly superior portion (larger grains exhibiting lower resistance) of the wire delay a signal more than HFs which travel under worse conditions (more contaminants & higher gain boundary density) & lower effective area? Is this some sort of venturi effect? ] See answer to #1. If the conductor IS different, then it would HAVE to affect the signal differently. Jon Risch
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