80W passive bass reflex subwoofer for 100V and 8 ohm sound systems
Canton - Power Sub 12 - Active Subwoofer
Amazon.com: Denon Home Subwoofer with HEOS Built-In, Deep, Powerful Bass, 8" Bass-Reflex Woofer, Pair with Denon Home Sound Bar 550, and Denon Home 150/250/350 Speakers or HEOS Speakers, Easy Installation : Electronics
RCF SUB-S10 Passive 10" Bass Reflex Subwoofer
Tech talk: what are bass reflex tubes? | Teufel audio blog