I have a set of Advent speakers... around 18-19 years old. The original woofers have DIAF. I want to replace them with a decent sounding woofer. I have seen Vifa being recommended on OT and some research has shown them to be a good choice. My problem: I can't remember what number on the specs I need to look at to determine if the woofer is close enough to work in the cabinets I have. Been about 15 years since I was building speaker boxes for cars and I knew all that stuff then, but have since forgotten. If anyone could guide me in the right direction, I would greatly appreciate it. TIA.