MVP21 GETSHOW 21 inch Powered Subwoofer Speaker Built-in Amplifier Active professional loudspeaker system - AliExpress
MT21A Built-in DSP single 21" Self-powered Subwoofer with Compact Cabinet Box - Buy 21" subwoofer, single 21 inch subwoofer, self powered subwoofer Product on Sanway Professional Audio Equipment Co., Ltd.