This design has been making the rounds at all the forums. It's a variation on an old theme done before by Peavey, Cerwin-Vega and a dozen others. The horn is too short to perform as a true sub; the F3 of 50 Hz is certainly nothing to get excited about from a 13 cu. ft box. Compared to modern designs such as the Lab or the EAW BH760 it really isn't competitive.