Check out this cool DIY on making your own subwoofer. I tried this before using some wood and plexiglass and it’s real fun once you hear the sub workin’
So I began to wonder if I couldn’t make something half decent myself. Ordinarily I wouldn’t attempt to build a loudspeaker; it’s notoriously difficult to work out the optimal dimensions of the cabinet; in addition sound woodworking and construction skills are required. However, a sub-woofer is somewhat different. First, there will typically be only one driver unit in the cabinet, so the design does not have to be a compromise between the needs of the multiple drivers. Second, the sub-woofer will be driven by its own amplifier and cross-over unit. This means the electronics can compensate, to a degree, for imperfections in the design, and we don’t have to implement a passive crossover (great big coils and what-nots).