doing 3 powerbass es15 these subs here (sorry about the chinese only site i could find that listed them.) Powerbass ES 15-D4 - Prodej-autohifi.cz
My box is 4.1 cubes per chamber with 4"x15.75" port its tuned to 33hz. i believe the recomended size was 3.5 cubes. will having extra space hurt...