From a Guy Kuo post:

"On occasion, you may be told that your subwoofer should be calibrated to produce an SPL which is 10 dB higher than the other channels. There is no need to do this with AVIA's subwoofer test tones because they are recorded 10 dB softer to automatically produce a 10 dB higher subwoofer setting when you target the same 85 dB SPL. If one wishes to be technically more correct, the 10 dB offset actually is only true if one is using an RTA to measure sound levels. We're using an SPL which would read about 3 dB lower for the same subwoofer setting. If you want to be completely correct, place sub level 3 dB lower at 82 dB instead of 85 dB SPL."

I use AVIA Pro and RTA for calibration, so I do use the -30dB/-40dB offsets. With SPL looks like you use 3dB difference.

I'm glad I only do this calibration very infrequently!

Mark

My Music : My Cinema