I recently dug out my long forgotten sub I put up together sometime ago, so I decided to pair it up with my DIY bookshelf speakers based on w12cy001 + XT25 to see how this setup would work. Amazingly, it got me exactly where I wanted - very close, if not over the KEF Reference 3 overall. It's a 28l closed box with JBL CS1210 car woofer that I found on sale for 40eur. Now that I got my appetite for low end in the open, I'd like to see if I could upgrade it to something even better. I can't see what the Fs is for this woofer, but probably not too stellar. I do run it with FreeDSP into Sure Electronics 200W class D mono block so I can adjust and flat it out pretty well, but there are probably still limits on how low it could go. Would a switch to GRS 12SW-HE with Fs of 22Hz make any sense? I wouldn't mind going even for something substantially more expensive if that would make audible improvement, considering I am listening mostly at lower levels.