Amazon.com: Subwoofer Amplifier Board, Arylic WiFi & Bluetooth 5.0,50W2 Stereo Pair + 100W Sub Class D Stereo Amplifier,Multiroom/multizone Home Audio Amplifier Board for DIY Speaker-Up2stream Amp 2.1 : Electronics
DIY Active Subwoofer : 15 Steps (with Pictures) - Instructables