SUB-4K / SUB-5T Active Subwoofer High Quality LowPass Filter Freq. 40Hz~250Hz+Bass Boost+Phase - Motronix
Amazon.com: Preamp Board 2.1 Channel Low Pass Filter Subwoofer Independent Interfaces for Full Frequency and Bass Output Tone Board HI FI Circuit Board DC 12-30V / AC 9-20V : Electronics
Subwoofer Active Low Pass Filter with Phase & Bass Boost control M-SUB6 | eBay
how to make low pass filter for subwoofer - Electronics Help Care
SUB-1STR Single DC 12-24V Active Low Pass Filter Crossover Subwoofer DIY KIT - Motronix