tonygeno,
Ian is correct. There is nothing wrong with the VP150.
What you are measuriing is an effect of pink noise, off axis reponse as well as the difference between drivers as you move right to left (tweeter W W W tweeter). To better demonstrate how the VP150 drivers create this effect, try out the following:
If you use your pink noise calibration on your main speakers (i have M60s), hold the SPL about 8cm away from the top driver and measure the dB. Then measure at the same distance moving down to the next driver and so on.
You will notice that each driver does not produce the same exact dB output with the pink noise. This is normal and occurs with the VP150 as well. The tweeters will not measure the exact same dB as the woofers. For a partial explanation, see
this link especially the short paragraph on the characteristics of pink noise.
As for the VP150 dispersion, you are reading into the dB measurements too much. The VP150 is so good at dispersion based partly on its great width. I've heard other single driver centre channels that really direct the ears to a single point. The multi driver and extra wide VP150 removes that effect very nicely while creating a wider sweet spot.
Keep in mind that sound will always change as you move in a room, not only because of room reflections but also because of the off axis response your ears perceive from each individual speaker. Try standing on your couch and listen to a song then drop down into the couch and listen again, then drop to the floor and once again listen how the sound changes. Off axis tests are fun but often make the family think you are truly a bizarre and confused individual.
