And as far as there "transient response" - please! No bandpass subwoofer system has any transient response. That's why its called a "subwoofer". The transients occur somewhere else.

A bandpass system has its front cavity tuned to be centered on the speakers resonance when placed in its rear enclosure. The front box size and port dimensions determine the system Q. Thus the bandpass system has substantial output below the speakers resonance! In any direct radiating system the system never has output below the systems resonance.

Bandpass system play louder and lower than any direct radiating system, but have limited bandwidth. In a subwoofer this is just what we want. All this talk about transient response, bandwidth, etc. is misguided when talking about a bandpass system because bandpass systems are INHERENTLY low bandwidth, slow transient response systems. But they do what they do better than a direct radiator ever can. And when properly mated with a mid bass system can work very well indeed.