How all of these elements are arranged constitutes the cable’s geometry. Some designers maintain that geometry is the most important factor in cable design—even more important than the conductor material and type.
An example of how a cable’s physical structure can affect its performance: simply twisting a pair of conductors around each other instead of running them side-by-side. Twisting the conductors greatly reduces capacitance and inductance in the cable. Think of the physical structure of two conductors running in parallel, and compare that to the schematic symbol for a capacitor, which is two parallel lines.
This is the grossest example; there are many fine points to cable design. I’ll describe some of them here, with the understanding that I’m presenting certain opinions on cable construction, not endorsing a particular method.
Many designers agree that skin effect, and interaction between strands, are the greatest sources of sonic degradation in cables. In a cable with high skin effect, more high-frequency signal flows along the conductor’s surface, less through the conductor’s center. This occurs in both solid-core and stranded conductors (Fig.2). Skin effect changes the cable’s characteristics at different depths, causing different frequency ranges of the audio signal to be affected by the cable differently. The musical consequences of skin effect include loss of detail, reduced top-octave air, and truncated soundstage depth.
A technique for battling skin effect is litz construction, which simply means that each strand in a bundle is coated with an insulating material to prevent it from electrically contacting the strands around it. Each small strand within a litz arrangement will have virtually identical electrical properties, pushing skin-effect problems out of the audible range. Because litz strands are so small, many of them bundled together in a random arrangement are required to achieve a sufficient gauge to keep the resistance low.
A problem with stranded cable (if it isn’t litz construction) is a tendency for the signal to jump from strand to strand if the cable is twisted. One strand may be at the outside at a point in the cable, then be on the inside farther down the cable. Because of skin effect, the signal tends to stay toward the outside of the conductor, causing it to traverse strands. Each strand interface acts like a small circuit, with capacitance and a diode effect, much like the grain structure of copper.
Individual strands within a conductor bundle can also interact magnetically. Whenever current flows down a conductor, a magnetic field is set up around it. If the current is alternating, the magnetic field will fluctuate identically. This alternating magnetic field can induce a signal in adjacent conductors. Some cable geometries reduce magnetic interaction between strands by arranging them around a center dielectric, keeping them farther apart—one of many techniques used by cable designers to make better-sounding cables.