What Is the Maximum Length for a Subwoofer Cable?

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Q In my current system, the receiver’s subwoofer output connects to an external amp linked to a passive subwoofer via a 20-foot length of speaker wire. The speaker wire runs under the floor and is tacked to the basement floor joists, where it crosses several household electrical wires. I would like to upgrade my subwoofer, but am having trouble finding one that is not self-powered. What concerns me about using a powered sub in my current setup is that the 20-foot coaxial cable run from the receiver to the sub would be susceptible to noise and interference. Are my fears unfounded? — David C.

A Not completely. While you could connect a subwoofer to your receiver using a coaxial cable longer than 20 feet and not experience problems, an RCA cable run that long is susceptible to electromagnetic interference (EMI) — especially if it crosses household electrical wires. With subwoofers, EMI can generate in a low-level hum that might very well be audible even when watching movies or listening to music.

To reduce the possibility of hum, try using a high-quality subwoofer cable with braid or dual braid-type shielding, a design best-suited for protecting against EMI. Another possibility is to go wireless. Wireless subwoofers, which are made by companies including MartinLogan and Klipsch, come with a transmitter that connects to your AVR’s subwoofer output and sends the signal wirelessly over the 2.4 GHz band to the sub’s built-in receiver. Wireless subs also provide an RCA-type line-level input should you choose to switch to using a wired connection in the future.

Yet another possibility is to buy wireless subwoofer kit, which will let you use any powered subwoofer you like. Such kits are available from Dayton Audio and Rocketfish (the Best Buy house brand) for around $60-70 and consist of a powered transmitter that connects to your AVR’s subwoofer output and a powered receiver that connects to the sub’s line-level input. With both wireless subs and kits, operating range is usually spec’d at around 12 meters — plenty enough for your current installation.

boulderskies's picture

You mention an external amp. If you use a powered sub, you dont need that amp and can connect the receiver to the sub directly. Would that shorten the path between receiver and amp? Nothing wrong with a powered sub-in fact, some think its preferred, relieving the receiver/amp of having to drive it and getting cleaner, more powerful performance.

Secondly, if that cable path is still required, if your cable runs at 90 degrees to electrical wires, that will greatly reduce the chances of any EMI issues.

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