Install Multiple Subwoofers in a Car

Get extra speaker wire, either copper or silver. A good rule of thumb is to double the amount of wire you'd use to install a single subwoofer for every additional subwoofer you're going to use. Whether you use a single power wire or multiple wires is up to you, though many experts say that a single wire makes the job easier and less confusing, since you can always keep track of where it leads.

Use a regular distribution block to split the power wire into its component parts, if you elect to use a single wire. (You don't need one if you're using a separate power wire for each subwoofer.) Use a fused distribution block if your subwoofers don't come standard with fuse protection. The distribution block allows you to input a single power source and output it to multiple applications (your subwoofers).

Connect each power wire, or the single power wire's distributions, from the low-level output of your stereo or CD player to the low-level input of each subwoofer. To do this, you'll have to unscrew and remove your stereo, since the low-level output is located on the back of the unit.

Run a grounding wire from each subwoofer to a metal grounding point that is at least 12 inches away from the battery that will be used to power the subwoofers. If you're using a distribution block, it can double as a single grounding point for all grounding wires. If not, it's better to use a different grounding point for each different wire.

Use RCA cables to send a music signal from your car stereo to your subwoofers. Your stereo or CD player should have auxiliary RCA cable outlets that you can use to connect it directly to your subwoofers. Link the two, turn on your subwoofers and play some music.