There are a lot of things that act as filters. The box, the mechanical movement of the driver, the electronics. So you're on the right track here. But the fact remains that whatever filters are used to modify response have the same result, no matter if they are mechanical, electrical or acoustic.Basically, whatever you do to modify the amplitude response also modifies the phase response. So if you do something that equalizes the characteristic response curve, you have also modified its phase response too. It really doesn't matter if the equalizer is an electrical, mechanical or acoustic filter, the laws of physics apply to them all the same. If you change the amplitude response by any means, then you must have also changed the phase response.