I bought this sub used for $20 to pair with my kef q15s.

After getting it home i found that it did not work.
I opened up the plate amp and found a few bad caps which i replaced with higher quality components. This is a fantastic sub! No hum as mentioned in the other comment but this may be a thing - just not a problem with my sub. a hum might be from bad wiring someplace external so maybe that guy has a bad preamp to sub? Idk. This sub has no hum and produces clean accurate bass that fills a room, brings kickdrum to life! I can hear the plucking and relief of guitar strings!! Clean tight accurate bass. I'd pay 2 bills for this sub but i think you can find them used for less.

This sub has a issue with ground hum.I don't think any body including kef has figured out what causes it.Ive taken sub to two authorized Kef repair centers which did not help with hum. I also switched receivers which helped alot but still sometimes it will go into a hum mode and needs to be rebooted then all is fine for another 6months.I also bought a Furman a/c line conditioner which made music and video better but sub still goes into hum mode.This sub has alot of adjustments so you can tailor sound for tight articulate bass or have chest pounding bass as much as can be expected for a 10" woofer.One would be fine small room but a second will be needed for large rooms.These subs can now be bought used for 200$ which is a steal.Excellent all around sub if you can live with occasional hum.