Hi Todd,
Thanks for your comments and your interest. Steve’s approaches, such as what you’ve described, sound like good ones to me. Regarding your questions:
Wider spacing of the two conductors will increase inductance and decrease capacitance.
The reason that inductance decreases when the conductors are twisted together, or at least brought closer together, is that since the currents in the two conductors are moving in opposite directions (one toward the load and one toward the source, at any given time, with the directions alternating between each half cycle of the signal in the case of AC), the magnetic fields created by those currents are in opposite directions and tend to cancel each other if the conductors are close together. To the extent that those fields do not cancel, the impedance presented to the signal will increase as the rate of change of the signal (i.e., its frequency) increases. For further explanation the Wikipedia writeup on
Lenz’s Law may be helpful.
Regarding capacitance, a capacitor consists basically of two conductive plates separated by a non-conductive dielectric, with each of the two terminals of the capacitor connected to one of the plates. As explained in the Wikipedia writeup on
capacitance the closer those plates are to each other the greater the amount of capacitance, everything else being equal. Similarly, cable capacitance presents itself as a shunt (aka parallel) phenomenon between the two conductors, and therefore increases as the conductors become closer together. While inductance and resistance present themselves as series phenomena.
In general, inductance is most likely to be significant in the case of speaker cables, to an increasing degree if the impedance of the speaker is low at high frequencies. (See my first post in this thread). Resistance may also be a significant factor in a speaker cable, of course, especially if the speaker has low impedance at many or most frequencies. Capacitance will usually be unimportant in the case of a speaker cable, unless it is very high, in which case it can cause problems for the amplifier. Especially if the amplifier is solid state and therefore most likely has low output impedance, and uses significant amounts of feedback, in which case even destructive oscillations can occur if the capacitance is extremely high.
In general, resistance and inductance will be unimportant in the case of a line-level interconnect, aside from the possibility that the resistance and inductance of the ground/signal return conductor can make a difference with respect to ground loop-related low frequency hum or high frequency buzz or noise, if the components involved are susceptible to ground loop issues. Capacitance can be important in the case of a line-level interconnect, especially if the output impedance of the component providing the signal is high. The interaction of that output impedance and cable capacitance will form a low pass filter, whose rolloff will usually begin in the ultrasonic or RF region, and therefore be inconsequential, but if those parameters are too high the filter can start rolling off and/or introducing phase shifts at frequencies that are low enough to have audible consequences.
For a given cable type, all of those parameters are of course proportional to length.
All of this, btw, pertains to analog cables. Completely different considerations and effects come into play in the case of digital cables.
And yes, crossing cables at right angles, or at least minimizing how much of their lengths are parallel and closely spaced, is good practice and will minimize or eliminate any effects the corresponding signals might otherwise have on each other.
Best regards,
-- Al
