The dielectric is the material surrounding the conductors, and is what gives cables and interconnects some of their bulk. The dielectric material has a large effect on the cable’s sound; comparisons of identical conductors and geometry, but with different dielectric materials, demonstrate the dielectric’s importance.
Dielectric materials absorb energy, a phenomenon called dielectric absorption. A capacitor works in the same way: a dielectric material between two charged plates stores energy. But in a cable, dielectric absorption can degrade the signal. The energy absorbed by the dielectric is released back into the cable slightly delayed in time—an undesirable condition.
Dielectric materials are chosen to minimize dielectric absorption. Less expensive cables and interconnects use plastic or PVC for the dielectric. Better cables use polyethylene; the best cables are made with polypropylene or even Teflon dielectric. One manufacturer has developed a fibrous material that is mostly air (the best dielectric of all, except for a vacuum) to insulate the conductors within a cable. Other manufacturers inject air in the dielectric to create a foam with high air content. Just as different dielectric materials in capacitors sound different, so too do dielectrics in cables and interconnects.
The terminations at the ends of cables and interconnects are part of the transmission path. We want a large surface contact between the cable’s plug and the component’s jack, and high contact pressure between them. RCA plugs will sometimes have a slit in the center pin to improve contact with the jack. This slit is effective only if the slit end of the plug is large enough to be compressed by insertion in the jack. Most high-quality RCA plugs are copper with some brass mixed in to add rigidity. This alloy is plated with nickel, then flashed with gold to prevent oxidation. On some plugs, the brass is directly plated with gold or silver or rhodium.
RCA plugs and loudspeaker cable terminations are soldered or welded to the conductors. Most manufacturers use solder with some silver content. Although solder is a poor conductor, the spade lugs are often crimped to the cable first, forming a “cold” weld that makes a gas-tight seal. In the best welding technique, resistance welding, a large current is pulsed through the point where the conductor meets the plug. The resistance causes a small spot to heat, melting the two metals. The melted metals merge into an alloy at the contact point, ensuring good signal transfer. With both welding and soldering, a strain relief inside the plug isolates the electrical contact from physical stress.