Amazon.com: Jovial One Channel Car Audio Mono Amplifier, 3900 Watt Max @ 1 Ohm High-Powered Mono Car Amplifier with Subsonic Filter and Low Pass Filter, Cooling Fans, White : Electronics
Subsonic Filters, protect your subwoofer from low bass using a multi-meter. - YouTube
Subsonic / Rumble Filter for Phono preamps and Sub-Woofers