Planar Speaker Asylum: R-C networks for speaker cables and other answers. by Al Sekela

This is an old technique, known as 'dynamic loading.' Ideally, you would use a resistor whose value matched the characteristic impedance of the cable, but 10 ohms works well if you don't know what the characteristic impedance is.

The resistor goes in series with a capacitor and the pair is placed across the end of the cable. You can use a pair at each end of each cable. The resistor absorbs energy from disturbances with enough high frequency content to get through the capacitor. The RC time constant with a 0.01 microfarad capacitor is 0.1 microseconds, so the corner frequency is 1.6 MHz. The impedance of the pair is high at lower frequencies and becomes equal to the resistor at higher frequencies within the pass-band of the capacitor.

All real capacitors have some stray inductance associated with their construction, so they have a resonant frequency above which they look inductive. For the R-C networks to function over the important noise range found in most houses these days, the 0.01 microfarad capacitor (which is 10,000 picofarads, or pF) should be bypassed by smaller units. Values around 1000 and 100 pF are useful.

As with anything in an audio circuit, the materials used have sonic consequences. The capacitor dielectric is in close contact with the speaker circuit. Teflon capacitors would be very expensive. I like the sound of silver-mica capacitors. Hosfelt Electronics has these for good prices, or you can pay full retail at Mouser. I like old-style Holco or PRP resistors from Michael Percy. There is negligible power at these frequencies, so the resistor size is not important. However, it does need to be a resistor over the important noise bands, so only film or foil noninductive resistors should be used, and not wire-wound.

Connecting these networks to the cables can be done by soldering them onto the cable ends, soldering them to spades and placing the spades on top of the cable spades, or, with Magnepan connectors, just sticking the leads into the wire sockets along with the cable wires, and tightening the screws. This makes it easy to experiment, to see if they help, before you commit to them by soldering.

Commercial versions of these networks are called High Definition Links and are sold by Walker Audio for a lot of money. They contain nude Vishay resistors and proprietary capacitors. I prefer the sound with the components I recommend over the Walker units.

As far as the inductors go, I've only used them in the positive tweeter legs. They should work the same in either leg, but I have not tried them the other way. Do remove the old tinning from the leads and retin with lead-free solder. I know they don't sound good in the midrange and bass driver circuits.

Considering how much harm RF noise can do, it is a shame that most amps appear to be designed without regard to keeping the RF out of the gain circuits. There may be some amps where this was taken into account: I'm not an expert on amp designs in the present audio market, so I don't know.