Interconnects are composed of three main elements: the signal conductors, the dielectric, and the terminations. The conductors carry the audio signal; the dielectric is an insulating material between and around the conductors; and the terminations provide connection to audio equipment. These elements are formed into a physical structure called the interconnect's geometry. Each of these elements-particularly geometry- can affect the interconnect's sonic characteristics.

Conductors are usually made of copper or silver wire. In high-end interconnects, the copper's purity is important. Copper is sometimes specified as containing some percentage of "pure" copper, with the rest impurities. For example, a certain copper may be 99.997% pure, meaning it has three-thousandths of one percent impurities. These impurities are usually iron, sulfur, antimony, aluminum, and arsenic. Higher-purity copper-99.99997% pure-is called "six nines" copper. Many believe that the purer the copper, the better the sound. Some copper is referred to as OFC, or Oxygen-Free Copper. This is copper from which the oxygen molecules have been removed. It is more proper to call this "oxygen-reduced" copper because it is impossible to remove all the oxygen. In practice, OFC has about 50ppm (parts per million) of oxygen compared to 250ppm of oxygen for normal copper. Reducing the oxygen content retards the formation of copper oxides in the conductor, which can interrupt the copper's physical structure and degrade sound quality.

Another term associated with copper is LC, or Linear Crystal, which describes the copper's structure. Drawn copper has a grain structure that can be thought of as tiny discontinuities in the copper. The signal can be adversely affected by traversing these grains; the grain boundary can act as a tiny circuit, with capacitance, inductance, and a diode effect. Standard copper has about 1500 grains per foot; LC copper has about 70 grains per foot. Fig.11-5 shows the grain structure in copper having 400 grains per foot. Note that the copper isn't isotropic; it looks decidedly different in one direction than the other. All copper made into thin wires exhibits a chevron structure, shown in the photograph of Fig.11-5. This chevron structure may explain why some interconnects sound different when reversed.

Conductors are made by casting a thick rod, then drawing the copper into a smaller gauge. Another technique-which is rare and expensive-is called "as-cast." This method casts the copper into the final size without the need for drawing.

The highest-quality technique for drawing copper is called "Ohno Continuous Casting" or OCC. OCC copper has one grain in about 700 feet-far less than even LC copper. The audio signal travels through a continuous conductor instead of traversing grain boundaries. Because OCC is a process that can be performed on any purity of copper, not all OCC copper is equal.

The other primary-but less prevalent-conductor material is silver. Silver interconnects and interconnects are obviously much more expensive to manufacture than copper ones, but silver has some advantages. Although silver's conductivity is only slightly higher than that of copper, silver oxides are less of a problem for audio signals than are copper oxides. Silver conductors are made using the same drawing techniques used in making copper conductors.

The dielectric is the material surrounding the conductors, and is what gives interconnects and interconnects some of their bulk. The dielectric material has a large effect on the interconnect'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 interconnect, dielectric absorption can degrade the signal. The energy absorbed by the dielectric is released back into the interconnect slightly delayed in time-an undesirable condition.

Dielectric materials are chosen to minimize dielectric absorption. Less expensive interconnects and interconnects use plastic or PVC for the dielectric. Better interconnects use polyethylene; the best interconnects 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 interconnect. 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 interconnects and interconnects.

The terminations at the ends of interconnects and interconnects are part of the transmission path. High-quality terminations are essential to a good-sounding interconnect. We want a large surface contact between the interconnect's plug and the component's jack, and high contact pressure between them. PHONO 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 PHONO 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, gold is plated directly to the brass. Other materials for PHONO plugs and plating include silver and rhodium.

PHONO plugs and loudspeaker interconnect terminations are soldered or welded to the conductors. Most manufacturers use solder with some silver content. Although solder is poor conductor, the spade lugs are often crimped to the interconnect first, forming a "cold" weld that forms 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.

How all of these elements are arranged constitutes the interconnect's geometry. Some designers maintain that geometry is the most important factor in interconnect design-even more important than the conductor material and type.

An example of how a interconnect'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 interconnect. 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 interconnect design. I'll describe some of them here, with the understanding that I'm presenting certain opinions on interconnect construction, not endorsing a particular method.

Most designers agree that skin effect, and interaction between strands, are the greatest sources of sonic degradation in interconnects. In a interconnect 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.11-6). Skin effect changes the interconnect's characteristics at different depths, causing different frequency ranges of the audio signal to be affected by the interconnect 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. Litz strands push 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 interconnect (if it isn't of litz construction) is a tendency for the signal to jump from strand to strand if the interconnect is twisted. One strand may be at the outside at a point in the interconnect, then be on the inside farther down the interconnect. 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 within copper. Individual strands within a conductor bundle can also interact magnetically. Whenever current flows down a conductor, a magnetic field is set up around that conductor. If the current is an alternating-current audio signal, the magnetic field will fluctuate identically. This alternating magnetic field can induce a signal in adjacent conductors (see Appendix B), and thus degrade the sound. Some interconnect geometries reduce magnetic interaction between strands by arranging them around a center dielectric, which keeps them farther apart.

These are just a few of the techniques used by interconnect designers to make better-sounding interconnects.

Interconnect and Interconnect Specifications

There's a lot of hype and just plain misinformation about interconnects and interconnects. Manufacturers sometimes feel the need to invent technical reasons for why their interconnects sound better than the competition's. In reality, interconnect design is largely a black art, with good designs emerging from trial and error (and careful listening). Although certain conductors, dielectrics, and geometries have specific sonic signatures, successful interconnect designs just can't be described in technical terms. This is why interconnects should never be chosen on the basis of technical descriptions and specifications.

Nonetheless, some interconnect and interconnect specifications should be considered in some circumstances. The three relevant specifications are resistance, inductance, and capacitance.

A interconnect or interconnect's resistance, more properly called DC series resistance, is a measure of how much it opposes the flow of current through it. The unit of resistance is the Ohm. The lower the number of ohms, the lower the interconnect or interconnect's resistance to current flow. In practice, interconnect resistance is measured in tenths of ohms. Resistance isn't usually a factor in interconnect performance (except in some of the new non-metallic types), but can affect some loudspeaker interconnects-particularly thin ones-because of their higher current-carrying requirements.

The sounds of interconnects and loudspeaker interconnects can be affected by inductance. It is generally thought that the lower the inductance, the better, particularly in loudspeaker interconnects. Some power amplifiers, however, need to see some inductance to keep them stable; many have an output inductor connected to the loudspeaker binding post (inside the chassis). When considering how much inductance the power amplifier sees, you must add the interconnect inductance to the loudspeaker's inductance.

Capacitance is an important characteristic of interconnects, particularly when long runs are used, or if the source component has a high output impedance. Interconnect capacitance is specified in picofarads (pF) per foot. What's important isn't the interconnect's intrinsic capacitance, but the total capacitance attached to the source component. For example, 5' of 500pF-per-foot interconnect has the same capacitance as 50' of 50pF-per-foot interconnect. High interconnect capacitance can cause treble rolloff and restricted dynamics. (A full technical discussion of interconnect capacitance is included in Appendix B.)