Hey guys I am selling ONE brand new PPI subwoofer to a friend and he asked me to build a box for him, problem is its been years since a built a box and I only have built 3 myself. He is looking to be able to listen to rock and rap, so i recommended a sealed enclosure for him. PPI's website recommends 0.6 cuft for a sealed and 0.5 cuft for an (SPL sealed enclosure ?). Should I stick to the 0.6 cuft or what else do you recommend for my volume? Thank you