Mr ibm, isn't your subwoofer self powered? Does it have a balanced input? Passive subs are much rarer but, if it is drop the wire to 12 or 10 gauge twisted pair or Kimber Kable 12 TC if you don't mind spending a lot of money. If the subs are active you can run a balanced line 300 feet if you want. Subwoofer drivers usually demand a lot of current so linear resistance matters. Lower gauges have lower series resistance. You want to keep induction as low as possible in a long run like that which is why you should use a twisted pair format vs Zip chord.