Nothing short-circuits subwoofer performance -- both literally and figuratively -- quicker than the wrong RCA cable or speaker wire. Lacking in signal delivery performance and sometimes allowing hum, the wrong cable takes what should be an exciting addition to your system and turns it into a frustrating troubleshooting experience. Basic issues such as shielding and thickness or gauge of each internal conductor and the overall length of the wire all matter when you're selecting subwoofer cables.
Shielding and Noise
Most electromagnetic and radio frequency interference affects subwoofer signals through induction. Similar to the way in which a piece of metal becomes magnetized, unshielded RCA cables will happily pick up and carry interference from adjacent equipment and noise from ground loops. A properly shielded directional cable rejects most inducted noise, while draining any noise present on the cable at the subwoofer. Additionally, RCA cables must be correctly soldered or crimped at the ends, because loose connections invite hum and radiated noise to penetrate into the signal.
Passive subwoofers simply refer to the lack of an internal amplifier. Passive designs are still amplified, but the amp itself is usually an a short rack, shelf or panel next to the speaker or among other pieces of equipment. The majority of car subwoofer systems use this topology. In this case, the RCA cable leading from the audio receiver to the amplifier should remain as short as possible, with the proper gauge of speaker wire chosen to lead from the amp to the subwoofer. Speaker wires should be 12 or 10 gauge, keeping resistance to a minimum. Resistance measures the degree to which a wire interferes with passage of low frequencies. Thicker wire over shorter distances allows an unfettered powerful signal to pass to the subwoofer. Higher-end subwoofer RCAs use thicker internal conductors to minimize resistance from the receiver or preamplifier to the subwoofer's amplifier.
Capacitance affects both RCA and speaker wires, although more relevant to the latter. Excess capacitance is particularly harmful to low frequencies and amplifiers. Capacitance describes how much energy is stored along a cable or wire, with the less stored energy the better. Excess capacitance builds when a cable is unnecessarily long, creating a progressively difficult load for the amplifier. At some point, the amplifier "sees" a dead short, causing the amplifier to shut down or go into thermal protection. In severe cases, this also causes oscillation in the amplifier, potentially damaging the amp and any speaker connected to it.
Copper and Silver
Silver cabling receives accolades among audiophile circles for its increased conductivity and higher cost. However, the advantages of silver are not relevant in the subwoofer world. High frequencies tend to travel towards the outside of a speaker wire. For this reason, many RCA cables and speaker wires plate their copper windings with the material. Subwoofers do not typically play anything over 120 Hertz, making the extra cost for silver wiring a waste. Lower-cost and more common oxygen-free copper is perfectly acceptable for low frequency applications.
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