Reference

Cable properties
The most obvious and easily quantified lumped-parameter electrical properties of cables are inductance, resistance, and capacitance—L, R, and C. Can variations of these parameters subtly alter the system sound? Yes, they can. Manufacturers rarely tell us what these values are, probably because it would undermine the frequently obscure technical claims made for their products. For a loudspeaker cable, the "complex" electrical load, which includes the loudspeaker, is connected back to the amplifier output port (and in many cases, in addition, to the inverting input via the usual feedback loop, depending on the amplifier topology; here, radio-frequency interference, or RFI, may interact with music signals' footnote 2). With many amplifiers, it is the noisefloor—the apparent quietness of the background—that influences subjectively judged qualities of transparency and stereo image depth, especially when auditioning cables. Advantageously, many cables are designed to minimize RFI.

If present in excess, cable inductance (L) may slightly dull high treble frequencies; high resistance (R) is rare, but when present, can (in combination with the other parameters) subtly alter timbre and cause bass excess. High capacitance (C) may add brightness—and even affect the electronic stability of the connected amplifier. In a connected audio system, all these parameters work in combination.

We also need to consider the high rigidity of some speaker cables (and some of the more physically heroic interconnect designs), in which—setting aside practical setup difficulties—unwanted longitudinal transmission of vibration between audio components may be an issue. Vibration may also be induced by the active soundfield or by power transformers. The superior compliance and damping of certain cables (and brands of cables) alleviate such problems. Vibrating current carriers can, in the presence of electromagnetic fields, cause microphony, which in turn induces reactive forces from the operating loudspeaker back to potentially sensitive electronics. An energetic longitudinal-mode vibration may be routed back to the amplifier binding posts.

Local vibration, be it floor-borne, soundfield-excited, or from the operating loudspeaker, may couple to the cable, influencing sound quality via potential mechanisms including triboelectricity in cable dielectrics; vibration and relative movement can be reflected in faintly audible modulation of the (otherwise) static charge. There are also piezo effects, particularly with plastics—polymers—which may react to vibration with an electrical response; PTFE is particularly active in this respect. Underlying such subtleties are those fundamental lumped electrical parameters, L, R, and C.

The simple resistance component is likely dominant. It is worth noting, however, that in moderation, pure resistance has a relatively small subjective effect on sound quality. Even a loop value of half an ohm is tolerable in many situations and could be largely mitigated by a modest adjustment of the speaker location in the room or the enclosure orientation with respect to the listener. That's not to say that you will not hear the benefits of a low-resistance feed. A low-resistance connection to the loudspeaker crossover maintains the designed timbre, minimizes distortion, and—not least—supports bass-driver damping and consequently low-frequency slam.

These are basics; there remain more subtle sound-quality issues. In interconnect cables, where wavelengths are far too long for "transmission line" parameters that could affect frequency response, the choice of insulating dielectric may contribute to sonic character, just as it does in film capacitors. Take your pick—PVC, PTFE, polythene, polypropylene—vibrations related to the music program induce electrical noise. (Knock a live microphone cable, and you'll likely hear a "bang" from the speaker.) Some exotic cables eschew the more electroactive polyolefin-based insulations (notably PTFE) and have reverted to "natural" fibers—linen, cotton, silk—which have rather less noise due to their more modest vibration signatures.

Ideally, digital interconnect cables are terminated with the correct impedance for the cleanest data flow, avoiding electrical reflections, but this is not always true. Even more subtle effects have been observed in digital audio transmission, rarely fully quantified but clearly audible.

Loudspeaker cables have many possible constructions, and nearly all have been realized: flat twin, spaced twin, ribbon, twisted pair, coaxial, helical, woven, and so on. Often these constructions influence not so much the primary audio signal as vibration damping and rejection of electromagnetic signals. Further helpful vibration-suppressing constructions include silk-insulated Litz. Concerning conductor choices, copper is by far the most common and the best value. The absolute purity has little effect on the brute-force low-frequency power, but to my ears (and the ears of others), it does have discernible benefit in high-quality systems at higher frequency signals. Six-nines purity (99.9999%) oxygen-free (OF) copper has a modest benefit at a moderate expense. Some other materials are favored over copper including linear-crystal OFC silver, silver-gold alloys, and even carbon-fiber Litz, which, however, is exceedingly difficult to terminate. Then there are more elaborate geometries, complex wire formulations, and custom electroplating of the conductors, often in silver.

Insulator dielectrics tend to have their own subtle acoustic signature, or color. The most neutral constructions are wholly or largely air spaced; consider the extreme example of the Kimber Gold interconnect cable, which has an almost entirely open weave, an open scaffold supporting largely air-spaced conductors.

Electrical interference induced in cable runs remains a factor. US inventor Robert Grodinsky of Robert Grodinksy Research and other companies thoroughly investigated sound-quality–related problems with cables and RFI, which he identified with powerful AM radio stations proliferating in cities, particularly New York. (This was in the tube-amp era.) He analyzed a circuit equivalent to a connected audio system including amplifier, cables, crossover, and loudspeakers. He observed that RFI from those many transmitters was leaking into the audio electronics and degrading sound quality with a loss of resolution and transparency and an audible degradation of the noisefloor. On occasion, his systems audibly demodulated broadcasts. His patented research into how to mitigate this interference is relevant today.

Robert was prescient. Prior art had not yet noted that even when no interference is directly audible, the infusion of RF energy into the system and on the connecting wires between the speaker and the amplifier can degrade the clarity and apparent dynamic range of an audio system. These time-displacement, distortion-induced reductions in fidelity are often substantial and give rise to very noticeable (subjective) feelings of "mushiness" and "compression" in the reproduced audio information (footnote 3).

Half a century later, many cable designs now include RFI control via inline termination boxes of varying size and complexity, long exemplified by MIT and Transparent Cable. Further, cable "lifters"—decoupling bridges and risers—may achieve some isolation from floor-coupled vibrations. Cables may include vibration "blockers"—mechanical interfaces—that attempt to blunt the longitudinal transmission of vibrations from one audio unit to another. The latter constructions are incorporated in the various Naim Super Lumina cables (see my Naim 200 series system review), among others.

When reviewing cable, the act of swapping out is often arduous, crawling about on the floor, wrenching connectors suitably tight, avoiding wire loops and cable crossovers while maintaining orientation and physical spacing. Good fieldcraft is essential for consistency, and frequent repeats are worthwhile.

Just as I was about to begin testing, I found that I had overused the heavy-duty terminals on my Karl-Heinz Fink (footnote 4) KIM loudspeakers, to the point where the threads were binding. To help get this review going, Karl sent replacement terminal panels by return with new Mundorf posts, and it took just a few hours to swap them in. Thank you, Karl.

Stereophile Editor Jim Austin asked me to run cable assessments on an ongoing basis, evaluating whole looms of cable from a single manufacturer and reporting on each set when the evaluation is complete. It was not practicable to test wholly unsighted, so my panel of listeners had to rely on each other to ensure a dispassionate approach, in a spirit of honest inquiry. It helped to run some practice sessions. My first assessment, on AudioQuest cables, appears elsewhere in this issue.

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Footnote 2: See my 2011 discussion (scroll down the page).—John Atkinson

Footnote 3: See patents.google.com/patent/US4597100A.

Footnote 4: Karl-Heinz Fink leads the Fink Team. Over a long career, he has worked with Denon, Mission, Mordaunt-Short, Naim, Q Acoustics, Tannoy, Wharfedale, and Yamaha, among other companies.