How much is this subwoofer worth?


A few years ago my Dad was given a subwoofer which was then left with me. I’ve had it a couple of years and I’ve decided to sell it but I have no idea how much it is worth. If I’m correct I think it is a Rockford Fosgate t212d4 12” made in 2004
zederick
The value of those older car audio subs are primarily driven by condition and rarity.  These aren’t very hard to come by but built like tanks.  You never stated what kind of shape yours is in but if its ‘new in box’ it could be quite valuable.  If it’s experienced a life of playing bass heavy music in the trunk of someone’s car for almost 20 years then it’s probably not going to be worth much.
Check the "Sold" listings on HIfiShark.com. Click on the "Sold/Expired" tab and then on the "Site" label at the top of the listings to narrow down the results to specific geographic areas.
https://www.hifishark.com/search?q=Rockford+Fosgate+t212d4