I don't have a way to test or measure that. It is an inch and a half rolled surround. It has a lot of room to travel.
I'm aware of the 1-1/2" half rolled surround, just thought you would know the Xmax. Guess one would have to consider it to be near the same as the SW-12A drivers throw.
Do you think you need to add more? The front diaphram is 5/8" thick MDF. Then there is a large bolt through the center of it with a lock nut on it.
Possibly, as it would have been a much smaller box using a (different driver). I'm very aware of your drop in SW-12A and the PR making up your nice sub kit.
Still planning to build 2 of the GR sub kits for a guy when he finally comes threw with the cash.
I was just curious..
Tanks
Geoff