The Old One, Two, Four
Line cables typically have either one or two conductors. Single-conductor cables (see Fig. 1) carry unbalanced audio signals from electronic instruments, studio equipment, guitars, consumer audio gear, and so forth, and they generally use tip-sleeve (TS) ¼-inch or RCA connectors to accommodate the conductor and shield (see Fig. 2). Braided shields are typical on unbalanced cable, although foil shielding is available for some unbalanced studio connections. Instrument cables (also known as guitar cables) are often designed for greater durability than studio cables and may include reinforced braided shields and extra-thick jackets.

FIG. 4: A dual-conductor cable with braided shield and filler.

Balanced audio signals are often used in professional audio gear, and they require dual-conductor cables (see Fig. 3 and Fig. 4). They also require XLR or tip-ring-sleeve (TRS) ¼-inch connectors (which look just like ¼-inch stereo headphone connectors) to accommodate the two conductors plus the shield. These cables come in many design configurations, and the shield can be either a braid or a foil, depending on the intended application. The two conductors are usually twisted together inside the cable to maximize the benefits of balanced connections. Twisting the conductors exposes them equally to any external interference, thereby increasing the efficacy of the noise cancellation that is inherent in balanced transmission.

A variation of dual-conductor cable is quad cable, which uses four conductors arranged in pairs. This configuration uses two conductors, twisted together and attached at each end, to form a single conductor. The two pairs are then twisted together, making a tight winding of all four conductors. Quad cables maximize the effects of noise cancellation in balanced transmissions by exposing all four wires equally to any interference.

Mic cables use either two conductors or a quad configuration and are similar in construction to balanced line cable. The difference is that good-quality mic cable offers increased flexibility and durability as well as reduced handling noise. Because they will be moved around in potentially extreme RFI and EMI fields, mic cables usually employ extra shielding. In addition, mic-cable jackets are typically made of a material that can withstand extra abuse and a wide range of temperatures.

A Higher Level

FIG. 5: This speaker cable has two insulated conductors. Note the lack of shielding and filler.

For most audio applications, cable shielding is necessary to protect audio signals from EMI and ES noise. Speaker cables, however, do not need such shielding, because they carry signals at a much higher current level, which means that any EMI must be very strong in order to be apparent. Nevertheless, speaker cables should be kept as short as possible to minimize cable impedance (more in a moment).

Speaker cable consists of two conductors inside a jacket or molded covering (see Fig. 5). To handle the high-current signals, the conductors are usually larger in diameter than mic or line cables.

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Reprinted with permission from Magazine, January, 2001
© 2001, Intertec Publishing, A Primedia Company All Rights Reserved