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Amazon.com: Universal Dual Bass Knob Volume Level Control for RCA Cable Audio Amplifiers Sub Gain Equalizer Regulator Frequency Controller RCA Line Level Adjust : Electronics
1x External Volume Bass Level Control Knob For Car Amplifier Subwoofer Speaker | eBay
Remote Subwoofer Level Control And Contr – Pyle USA
Kenwood P-XRW1202WB 12" Subwoofer in a Sealed Wedge Enclosure with a X502-1 eXcelon Series 1000W Max Power Class D Mono Amplifier with a KCA-RC01A Wired Remote Level Control - Creative Audio