Eight Audio - EASC01 - Active Sub-Woofer Filter with Phase, Gain & Freq. Adj.
Low Pass Subwoofer Filter Dc 12v Single Power Supply Heavy Preamp Hifi Pre-circuit Non-amplifier Sound Box - Integrated Circuits - AliExpress
Aiyima Low Pass Filter Bass Subwoofer Preamp Amplifier Board Single Power Dc 9-32v Preamplifier With Bass Volume Adjustment - Home Theater Amplifiers - AliExpress
SUB-1S Single DC 12-24V Active Low Pass Filter Crossover Subwoofer DIY KIT - Motronix
Subwoofer filter Board With 5 Preset Adjustable Frequency Setup - Soldering Mind
Subwoofer Filter Circuit Using Op-Amp TL072 under Repository-circuits -21250- : Next.gr
Low Pass Filter Circuit for Subwoofer | Homemade Circuit Projects
SUB-2 Active Subwoofer LowPass Filter High Quality Freq.40Hz~400Hz+Bass Boost+Phase Control - Motronix