It seems like alot of sub companies are making odd sized subs now. Crutchfield has 11", 13", 13.5", and 16" subs. I remember back in the day when all you could get was 8, 10, 12, or 15's. With the strange sizes, its gotta be a pain in the ass to find pre-made sub boxes to hold them. Guess they want people to start making their own boxes to hold the new sizes.

 

It's all nominal anyway, what with 3" of the cone taken up by the fat roll surround. Odd sizes have been around forever. When I was a kid and started reading audio magazines, they already had 2,3,4,5,6,7,8,9,10,11,12,13,15,18" speakers, and some were the closest-equivalent of the original metric (305mm=12" etc)

 

Some companies make the odd sizes because they claim they will push out more air than the traditional 10, 12, or 15's. However, like Stocker said....usually the odd sized ones have a bigger than normal surround, so it doesnt really matter.