I am listening to music using a pair of ML motion 12s and my old JBL L88s. I added the JBLs to provide some lower end bass the ML don't have and the combination has been very pleasing. However I am about to hand down the JBLs to my son and I am beginning to consider other options. Would like to hear some thoughts on adding a sub vs adding some less expensive speakers that might fil the base needed. Would like to keep the cost under $600. This is for a small 150 sq ft listening room and I listen mostly to R&R, jazz on vinyl so I am not looking for booming bass. Running speakers from a Cambridge 650a.
low frequency extension adding a sub makes sense. I would look at subwoofers that are sealed, servo controlled, and exhibit low Q. Unfortunately, you probably cannot get that for less than $800, unless you buy used. That said, you could do a lot worse than an Epik Legend for $500 to go with Martin Logan Motion 12s. If you can spend a little more, the SVS SB12-NSD at $650 would be good also. Ultimately, the Rythmik subwoofers are probably one of the best for music under $1000.
I am not concerned with the sub being sealed than with it incorporating decent EQ to compensate for room modes. That, imho, is the major influence on in-room performance.