Just a suggestion after many years of getting bass output. If you truly want a sub woofer you will need to get speakers with an f3 cutoff well below 20 hz. If you want to keep the next octave of bass clean, you will need to set up a system with the first octave on some very efficient large speakers with lots of clean power to drive them. An electronic crossover to a second set of woofers to cover the range from 40 to 80 hz on clean power and then the mains for the remainder of the musical spectrum. If you try to cheat this formula with LOUD bass the cone excursions will color the next octave of music with doppler.