Davis, Fred E.
Effects of Cable, Loudspeaker, and Amplifier Interactions
(1991) J. Audio Eng. Soc.,Vol.39, No.6, pp 461-468
Abstract
Loudspeaker cables are among the least understood yet mandatory components of an audio system. How cables work and interact with loudspeaker and amplifier is often based more on presumption and speculation than on fact. The literature on loudspeaker cable behavior and effects is minimal. Measurements were made with 12 cables covering a variety of geometries, gauges, and types. The measured data indicate distinct differences among the cables as frequency-dependent impedance, subtle response variations with loudspeakers, and reactance interactions between amplifier, cable, and loudspeaker. In some cases the effects of the amplifier overwhelm the cable's effects. Mathematical models that provide insight into the interaction mechanisms were constructed and compared to the measured data.
Conclusions
If loudspeakers were only simple resistance, then large, low-resistance cables would not be a bad idea. However, loudspeaker systems exhibit frequency-dependent complex impedance that can interact with the reactive components of amplifier and cable. The best response was obtained with low-inductance cables and an amplifier with low-inductance output and a high, frequency-independent damping factor.
These tests have shown that the best way to achieve adequately low resistance and inductance in a cable is by using many independently insulated wires per conductor rather than one large wire. Efforts to reduce the skin effect (such as Litz construction) will help, but due more to the reduction of inductance than the reduction of the skin effect. Inductive reactance is more significant in large cables than the skin effect. If an amplifier does not disagree, larger capacitance in a cable is not significant since this component is comparatively small and reduces amplifier and cable inductive reactance effects.
The best performance was measured with the multi-conductor cables Spectra-Strip 138-064, Kimber 16LPC, and AudioQuest Litz. Smaller multi-conductor cables such as Kimber 8LPC, Kimber 4PR, and Spectra-Strip 191-036 also performed well.
Of the two-wire cables, 12 AWG provided the best Interface, with reactive loads, while both smaller and larger gauges (3-7 AWG and 18 AWG) showed greater high-frequency drop and interaction with capacitive reactance in a load. 12 AWG seems more than adequate, even for demanding systems, high power levels, and reasonable lengths.
The effects of 3.1-m cables are subtle, so many situations may not warrant the use of special cables. Low-inductance cables will provide the best performance when driving reactive loads, especially with amplifiers having low damping factor, and when flat response is critical, when long cable lengths are required, or when perfection is sought. Though not as linear as flat cables, 12 AWG wire works well and exceeds the high-frequency performance of other two-conductor cables tested. By the way, keep the auto jumper cables in the garage!
All this is well and good. But it avoids the larger question. Do any of these measurably different electrical parameters lead to differences that listeners can actually hear?
