subwoofer volume process circuit stereo low-pass| Alibaba.com
NE5532 Bass Subwoofer Preamp Board Adjustable Low Pass Filter Board Pre-AMP Amplifier Module DC 10-24V Power Supply
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