I'm going to second soundhound's comment -- there is no need to match speaker cable length. I have 2-meter cables on my left and center channels, 2.5-meter cables on my right channel, and between 25 and 40 feet to each of my three surrounds (6.1 system). Now if you are bi-wiring, I would recommend using equal lengths of the same kind of wire (although some people do use different cables for the low and high on bi-wired systems), but I could see an argument even there against worrying about it. I'd recommend 14 gauge or 12 gauge for the wires, particularly on the longer runs (20'+).

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