DS18 PRO-BX21N.2 21" Neodymium Woofer 6000 Watts 6" 2-Ohm SVC audio car home system Subwoofers
2) B&C 21SW152-4 21" Neodymium Subwoofer 4-Ohm DJ Live Sound 4000Watts Bass Sub
RCF SUB-8005AS Single 21″Active High Power Subwoofer – Sonic Circus
AccuGroove Whappo Grande Bass 21" Subwoofer – AccuGrooveLLC
MVP21 GETSHOW 21 inch Powered Subwoofer Speaker Built-in Amplifier Active professional loudspeaker system - AliExpress
Earthquake 21 Subwoofer Build Plans! – Toid
Apocalypse DB-SA521 NEO | 21 inch Subwoofer
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.
Sledge M6-21 6.0cuft Subwoofer Flat-Pack for 21" Subwoofers