My design is the sealed box design because I already had two subs. As the spec's indicate, the lower end started to decline at around 70 Hz and we set the processor to crossover at 60 Hz. This created a seamless integration of sound for bass, midrange, and treble. The Vifa's do a great job of extension even without the subs and what can be said of the ribbons...they're just fantastic sounding. As expected they project a very wide soundstage but you need to be seated for critical listening as the vertical dispersion is limited.I have not run any test CD's yet because right now we doing some re-remodeling to the ceiling and installing room treatments. As soon as this is completed, I will evaluate them further and you may email me for my thoughts.