Starke Sound SW15 and SW12 Sealed Subwoofers Review | Audioholics
What is a subwoofer, and do you need one? - SoundGuys
Amazon.com: 2X SoundXtreme ST-412 Premium Elite 12 Inch Car Audio Subwoofer 4000 Watts Max Power for Pair Dual 4 Ohm Voice Coil High Power Bass Surround Sound 12" Sub Speaker System Pair : Electronics
What Is a Subwoofer? How Bass-Focused Speakers Work