8 Chapter 1 1.6 Loudspeaker Cables It would be somewhat off-topic to go into a lot more detail about loudspeaker cable design, but this might be a good place to point out that there is absolutely nothing magical or mysterious about them. My findings [3] are that, looking at the amplifier­cable­loudspeaker system as a whole, the amplifier and cable impedances have the following effects: · Frequency response variation due to the cable resistance forming the upper arm of a potential divider with the loudspeaker load as the lower arm. The effect of the resistive component from the amplifier output impedance is usually negligible with a solid-state design, but this is unlikely to be the case for valve amplifiers. This is at least potentially audible and is a good reason for using thick cables. It is not a good reason for using anything other than ordinary copper cable. A high-frequency roll-off due to the cable inductance forming an LR lowpass filter with the loudspeaker load. The amplifier's series output inductor (almost always present to give stability with capacitive loads) adds directly to this to make up the total series inductance. The shunt capacitance of any normal speaker cable is trivially small, and can have no significant effect on frequency response or anything else. · The main factors in speaker cable selection are therefore series resistance and inductance. If these parameters are less than 100 m for the round-trip resistance and less than 3 H for the total inductance, any effects will be imperceptible [3]. These conditions can be met by standard 13-Amp mains cable. (I'm not quite sure how the equivalent cable is labelled in the United States.) This cable has three conductors (Live, Neutral, and Earth) each of 1.25 sq mm cross-section, made up of 40 × 0.2 mm strands. Using just two of the three conductors, a 100 m round-trip resistance allows 3.7 metres of cable. The lowest cable resistance is obtained if all three conductors are used, normally by paralleling the Neutral and Earth conductor on the cold (grounded) side of the cable; the maximum length for 100 m is now 5.0 metres, which should do for most of us. This three- conductor method does give what I suppose you might call an "asymmetric" cable, which could offend some delicate sensibilities, but I can assure you that it works nicely. The loudspeaker cables that I have in daily use are indeed made of such 13-Amp mains cable, bought from an ordinary hardware shop nearly 40 years ago. Should a passing audiophile query the propriety of using such humble cabling, I usually tell them that with so much passage of time in regular use, the electrons have been thoroughly shaken loose and move about with the greatest possible freedom. I do hope nobody reading this book is going to take that seriously. 1.7 The Advantages and Disadvantages of Active Crossovers Here I have tried to put down all the advantages and disadvantages of the active crossover approach. Some of them may not be very comprehensible until you have read the relevant chapter of this book. My initial plan was to attempt to put them in order of importance, but