when you lose the 6 screws on same driver equally and sound changes then what exactly you feel is changing in sound. I do not mind you reporting that sound change but I still not at ease that you associate the change with phase. I do not think it has anything to do with phase and therefore I ask what subjectively you fell is changing while you change force on the screws. It would be very simple to confirm if the changes you report have anything to do with phase – just run impulse test with loops and tight screw and you will see if the phase was affected. I do think that you deal not with phase but with damping and resonances….