A subwoofer, built with me in a closed box with 56 liters net. As SW for a DIY 5.1 system a dream. Strong, but not obtrusive bass. For electronics hobbyists: subsonic filter is recommended active crossover Linkwitz. Bass correction calculated value: approx 24Hz. For experiments, a phase controller is recommended. DIY power amplifier and crossover and Processing. Suggestions for this purpose, among others, sound.westhost.com