I am thinking about swapping out my 4 18's for 4 15's so I can build a proper size box. The 4 18's are in a 16 cube box and it is still definitely loud its just I think if it was bigger it would be better. I can get the RD alpha max 15's and build a proper size box for them and not be so close to the roof/hatch and I think get more air movement. Powered by two Sundown 3000's. I know RD's customer service has problems but getting the subs from a member so don't have to deal with RD.