Usually a 75 ohm shielded cable but yep, pretty much a RCA cable.
If all you have is a RCA try it, as long as you don't pick up a hum or buzz you are good to go, if you do, you may need a shielded cable.
If you need to buy one be sure to get it at Monoprice or BlueJeans. A good sub cable should cost you 10 bucks or so.