Found this on the MTX site. Due to the fact that all the sound from this type of enclosure is produced by the vent, sound quality may not be as good as that of a properly designed sealed or ported enclosure. However, there are times when bandpass enclosures are the best choice to use. In a sedan application, bandpass enclosures are often used due to the inability to have multiple drivers mounted in the rear deck. In a limited space situation, efficiency can be sacrificed to gain deeper bass extension. In a situation where ultimate SPL is the goal, you can sacrifice bass extension, and enclosure size to produce a very efficient enclosure. Efficiency gains in the range of 5-10dB are not uncommon! As with any enclosure design, there is no free lunch. As you change one parameter to gain another, many times sound quality is degraded as well. The frequency response in the pass band of a single reflex enclosure can be described with an “s factor”. S values that are of interest to us fall between .7 and .4. Values beyond this range either have peaky response, or poor sonic quality. An s of .7 refers to the flattest pass band available, where an s of .4 refers to the widest useable pass band.