I got this sub as a throw-in with the purchase of a pair of ML ESLs. It puts out plenty of sound for a small to medium sized room. Response down to the low 30s Hz range and work very linear with the ESLs.The list price for this speaker is sort of high for its class but should not be overlooked as a stand alone sub.
Don't let the good looks fool you. The Martin Logan sub-woofer produces awesome low end sound in a 13 x 20 room. It's like being in a movie theater. I like the panel adjustments and if you wanted to do it, it's possible to hook up two of these. No questioning the quality. The one drawback is the packaging used by Amazon. There isn't any. They just ship it in the Martin Logan box, which is not particularly strong. Mine came with lots of holes and scared me to death when it came.
I purchased this subwoofer on January 17, 2012. Today it is July 24, 2015. Like many of the reviews here, my unit started the loud humming sound even when everything is disconnected from the woofer. It looks like the mean time to failure for this woofer is about three years... rather disappointing.
After four-year light using (less once a week), it started to make loud noise without any wire connection when standby. I talked to the technical support of MartinLogan. He said that he can send me a back plate for >$250 (plus S&H). I just gave up. Made in American was ruined by them.