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

Technically, the Hsu is as good as it gets at this price point. That doesn't mean it'll sound best to you, in your room, with your mains. But it is worth an audition. (Try to find somebody who has one; otherwise, you've got to order one on the 30-day plan.)

Paradigm PDR-10 ($350) or HSU VTF-2 ($500)

B&W ASW 600 sounds good to me. 10 inch 150watts. $500. I'm fairly new to the high-end stereo game but this is what I own and it's nice and tight for music. Some of the others that I listened to(including HSU) sounded way to boomy for me. I have a pair of B&W 602's and the sub blends in perfect with it. You can't tell that it is there.

VMPS New larger subwoofer..it sells for 700$..I don't think you can find a used one..no one sells them on the used market..why?/because they are so good.....

The Aperionaudio 12 recently had quite a good review.