Well a bandpass box is just that. It uses the port tuned to a specific frequency to enhance the bass boost at that level. It acts as it's own sort of crossover. Preventing highher frequencies from being reproduced by the sub. Not really... but you don't hear them. A sealed box will generally give a better kick because of the resistance built into the box offering the surround a little more protection from being overdriven. Whereas a ported box has less resistance in the enclosure and allows the excursion to be maxed out however the port is tuned to a specific frequency giving a boost at that level. The main diff tween a bandpass box and a regular ported enclosure is that in a bandpass the subs are enclosed entirely inside the box and a ported box has the cones facing the elements. The subs inside the bandpass give the best of both worlds. The inside chanber usually where the subs are facing is air tight. Thus creating thaty resistance the subs require w/o over exerting them when supplied high power at loud volumes. The back sides of the subs are ported and tuned to a specific frequency and the air coming out of that chamber resonates at the tuned frequency. thus giving a greater db level at that frequency.
Hope this helps You can email me for further clarification.