it depends on what you want... a small sealed enclosure will let you pump more through the sub and sound alot cleaner. a large box needs less power and sounds alot boomier... i dont know how tto describe boomier but the subs move easier then in a small box. building a box right depends on what you want to hear and the equipment that will be going into the box! if you have a weak amp i reccomend building a bigger box.... http://www.diysubwoofers.org/ browse this site and it hase some helpful hints but it is a bit harder to fallow!good luck!