QED PROFILE Audio RCA to RCA – 5 m

The QED Profile RCA to RCA cable is a stereo analogue interconnect terminated with two phono plugs at each end, supplied here in a 5 metre length. Five metres is a long run by interconnect standards, and it is chosen for a specific reason: to reach a power amplifier, an active subwoofer or a second system that sits some distance from the source equipment.

Length is the variable that changes how an interconnect behaves. A short interconnect can be built almost any way and still work; a long one has to be considered. Two effects dominate. The first is capacitance, which accumulates with length and forms a low-pass filter with the output impedance of the source. Valve equipment and passive preamplifiers, which have high output impedance, are the cases where this can become audible at the top of the range; most modern solid-state outputs drive a run of this length without difficulty. The second is interference, since a longer cable presents a larger area to pick up mains hum and radio frequency energy, which makes shielding coverage the property that actually matters.

Installation habits matter more at this length than at one metre. Route the cable away from mains leads rather than parallel to them, and cross any unavoidable mains cable at right angles so the coupling area is minimised. Avoid coiling the surplus into a neat loop, which turns it into an inductor.

If the run is longer than this and hum proves persistent, a balanced connection is the structural solution; within five metres, a properly shielded unbalanced cable and sensible routing are normally sufficient.