Advice on replacing 12 in woofer in Martin Logan Monolith III's

This was years ago, I did volume it using bean bag fill because it's an odd shape looking for the right driver, but I didn't log it down, don't hold me to it but I think it was 3 cubic feet.

Cheers George  

@georgehifi 
@stevepa
if it indeed 3 cu ft... this is expensive ($245 each), but ran curves F3 in QB3 alignment is 25hz 
Peerless  835017
If the box is a smaller, there are others that can work for less money.

again, based on 3 cu ft......

ScanSpeak Discovery 30W/4558T   This looks good.

Peerless 835017

I think I remember looking at this, but remember the the distortion was better at 150hz on the SV-12. But the main thing for memory that turned me off it was that it’s only 83db where the SV12 was 89db and the ML panels are also 89db.

Cheers George