Why would the type of metal make any difference in the phase shift? I'm truly interested in knowing how this could be so...
Copper vs silver conductors will not cause a phase shift in you application. Over long lengths of cable the different resistivity of the conductors and, more importantly the different cross sections of the conductors would interact with the I,C, and R characteristics of your speakers to cause a phase shift. However, you are likely not talking about using #6 copper and #28 silver or having runs of 100's of feet. As to an advantage of using silver for the high end and copper for the lo end, the effects of the differences in the R,C, and L values of the two cables are going to be swamped out by the rest of the system. However, you may find it personally valuable in determining the merits of this type of tweaking to obtain your own data by conducting your own experiments. In brief - create your own blind study. Start with generic # 12 cables as one system and the small silver and large copper system. Find a way to hide from yourself which cable system is which - whether hiding the cables in identical unshrinked heat shrink coupled with something to make the diameter look the same - using some type of flexible conduit or pvc or some other method of keeping yourself in the dark as to what cable is being used at any given time. Mark the cables inside the heat shrink. Mark the cables on the outside so that each day you strip off a marking and have another marking underneath. Record your impressions from listening on a day to day basis. At the end of some period of time that gives you a decent number of samples - say 50, remove your controls and see what your results tell you. As to methodology, my suggestions were on the spur of the moment and I would certainly put more time and thought into the experimental setup and how you achieve the necessary controls.
I didn't think different conducting metals would create phase/timing issues over such a short run (8ft) but it costs nothing to ask!
My question was inspired by having bi-wireable speakers, and equal lengths of heavy copper cable and silver cable; I might give it a try.
As for Musicnoise's experiment, I might get around to that when I have a bit more time; I don't think I can vanish into the front room for that long without raising the ire of the wife & kids!
Were you able to ever conduct Musicnoise's experiment? What were your results? Has anyone been able to do the test above and care to share their results? It sounds really cool but I could never execute it. No time or patience on my part. I'm getting listening fatigue from my system right now and it may be the new Zu Wax SCs I just got. I'm just starting the 200-300 hour break-in time. If the fatigue doesn't subside after some time I was thinking about using silver SCs on the highs of my Kefs and the Zu Wax on the lows. They are really nice well built cables.
I have a pair of PS Audio XStream Statement Bi-Wire speaker cables. Bought 'em on closeout in 2005, so they were probably a 2003 or so product. When they were manufactured, they were the only cables designed specifically for bi-wiring. That is, the bass run was optimized for LF transmission and the treble run was optimized for midrange/treble. As such, the bass includes 3 or so very thick solid core copper conductors making for about a 6 ga. conductor. The treble run consists of smaller strands of silver-plated copper. For my bi-wirable Mirage M5si's they were just what I was looking for. They soundly trumped the MIT MH-750 double run I'd used before, and the signal transfer is so efficient I no longer felt a need to bi-amp these speakers.
The transparency and immediacy of the speakers improved significantly and the imaging and treble are very nice. Physically these cables are ridiculous--2" diameter and they weigh about 2 lbs. per foot per side. The cable is so heavy it's been known to snap off the banana plugs and I use a C-clamp to keep the cable from pulling my center channel speaker off its shelf.
But the sound makes 'em worth it.