Here's a good tip from Guy Kuo. Works very well.

Using AVIA Phase Tests to Fine Tune Speaker Distance and Delay

AVIA's speaker phase testing signals are also useful for very accurate adjustment of speaker delays and distances. You'll need an analog RS SPL meter set to fast response in order to take advantage of this tidbit. This may seem a bizarre way to check delays and speaker distances but it is surprisingly accurate.

The phasing tests work by playing noise in the two channels being tested in phase and 180 degree out of phase intermittently. If the speaker distances and delays are both set correctly, then the in phase sounds from both speakers reinforce each other at the prime listening positioning. During the out of phase (diffuse) portion of the test, the sounds cancel. An SPL meter set to fast response can readily show the magnitude of the cancellation/reinforcement.

Start by playing the Phase left front/right front signal. Move your SPL meter slowly left and right at your listening position. If you have set distance and delays correctly the maximal SPL delta will occur in the middle of your sitting position. I get about a 6 dB needle bounce on my system. If it happens right of center, then your right speaker is either too farther away than the left speaker or delayed more than the left speaker. Conversely, if the peak SPL delta occurs left of your prime listening spot, the left speaker is too far or excessively delayed.

Once you have the front left and right speaker distanced and delayed exactly right, the SPL meter position at peak delta will be in the middle of your prime listening position. Note that position carefully. You'll need to be able to refer to that point within half an inch during the next step.

Now comes the trickery that gets the center speaker also precisely phased and delayed. The AVIA disc also has a Phase Left Front/Center test. We can take advantage of it to bring all three front speakers into very tight phase alignment. From the previous step we already know where the two front main speakers are in phase. Leave the left and right delays and speaker positions alone now. We'll next adjust the center speaker to be in phase with the left front. This places all three into phase.

Play the Phase Left Front/Center test and once more move the SPL meter left and right to find the maximal SPL delta point. Compare this new position to the one for the front mains. If all is perfect, they exactly coincide. If the left/center maximal SPL delta point is left of the left/right point, then the center speaker is either too close or insufficiently delayed. If the left/center max delta point is right of the left/right max delta, then the center speaker is too far. Move or adjust CENTER channel delay as needed to get the left/center max SPL delta to occur at the exact same place as for the left/right channels.

Your left, center, right speakers are now in phase. You'll probably note that a 1 msec adjustment in channel delay makes for a considerable shift in max SPL delta position. After all, that is about a 1 foot speaker distance equivalent. Use very small speaker movements to fine tune the center speaker into phase alignment.

Put your head at the center of the max SPL delta position and listen to some stereo and 5 channel material. You will be pleased with what has happened to sound imaging in your system.

Moving your speakers to achieve exact phase match isn't the entire story. One must also position the speakers with relation to room acoustics to smooth frequency response. Sometimes, moving speakers into exact phase also moves one or more of them into positions that yield uneven frequency response. In such cases, some compromise is needed to address both imaging and frequency response concerns. Happily, the home theater sound processor does have delays and these can sometimes help bring speakers into phase, while still keeping them closer to best tonal balance position.