For starters you want to check that you are working with a single 2 ohm subwoofer by looking at its basket. Your single subwoofer should only have one set of terminals, one positive and one negative, otherwise you may have a dual voice coil subwoofer.
Now prior to wiring your woofers you always want to verify the impedance of the sub using a digital multi-meter by attaching the test leads to the terminals. When reading the impedance you want to be sure the subwoofer is facing upwards and most importantly on a flat surface due to an easily disrupted false reading.
When attaching your leads, one to negative and one to positive, join a jumper cable (positive to positive and negative to negative) and attach to the second subwoofer. When your subwoofers are wired parallel, as shown in the photo, retest the impedance with the multi-meter and verify it reads at 1 ohm.
There you have it! Easy wiring to have more subwoofers to your audio system without too much hassle. For more information, see our Sonic ‘How To’ video on wiring Single 2 ohm subwoofers to 1 ohm here or Sonic ‘How To’ video on wiring Dual 2 ohm Subwoofers to 1 ohm here.