ok so i got my subs today and i started reading the lil booklet with them. im at the part where it explains the boxes for it. it says optimum is the largest and most efficient and that compact is efficient and good for tight limited spaces. it then goes on to say the optimum specs are 3.0+PD(port displacement) it then says that the compact specs are 4.0+pd
now im not a genious by any menas but isnt 4.0 bigger than 3.0
so is this some top secret code i dont understand or is my booklet a typo?