So then I'm cutting it too close? It's a sealed 1 cu ft box for a single 12 and a PG sub I have to put in a on old beater. But if it won't work I may have to figure something else out.
Yea, that's cutting it close. I usually give it at least 5". My current setup has about 10", and they barely get warm to the touch after some seriouse cranking.
A proper enclosure could make or break a sub. Why would you waste time and money on an old beater? That's like putting in a turbo charger in your car and then downgrading the tires to golfcart wheels.