I need a musical sub under 500,,,,new or used.

Paradigm PS-1200 Subwoofer. This is a really good sub for music and movies. Alot of reviews on Audioreview about it.

Believe it or not, about ten years ago Pioneer made a subwoofer called the "SW-1000" that is remarkably fast and musical.... I have one in my second system and while it's certainly not as quick and won't go as deep as my REL Strata II, or play as loud, it performs a lot better than you might imagine. The Pioneer has speaker-level inputs which are very transparent-sounding and 12" paper cone woofer that is quick and tuneful. It is without doubt more musical than bandpass-type subs (like the Paradigm PS1200) and IMO more musical than the budget Velodyne, Klipsch, JBL and other low-end (10" woofer) subs. I've seen them go for about $100 on ebay which is a stone-cold bargain considering the performance you can get from this 20" square black box. As an added extra the Pioneer is quite attractive looking with a piano-black top and front-mounted controls. Oh and BTW, I use mine with an ASL Wave 8 tube monoblocks and Triangle titus speakers and it holds its own with this budget audiophile gear.

Adire Audio - rava $399. Sealed 12" Shiva based sub. I am real impressed with mine.