phase shift control

can any one tell me how a phase shift controller works.?

thanks again

It works by changing the electrical phase of the speaker.  Like swapping the + and the - speaker wires.  Since the acoustic phase between the main speakers and say a subwoofer can shift (what you actually hear is affected by the environment, reflections, time delays, etc. and can cause sounds to arrive at your ears out of phase from when they were produced by the speaker) being able to change the electrical phase can allow you to compensate.

In general, set up your system and play a track you are very familiar with.  Set the subwoofer amp to "0" phase.  While the music is playing, have someone switch the phase around.  Stop them when the bass becomes the strongest.  You will have (approximately) aligned the acoustic phase of the sub to the mains.

so is it a good thing to have ot not? will it sound better with it? can u put is on a momo set or stereo set up.