Which one is more accurate for audio calibration, avia calibration disc or my onkyo receiver? I tested both of them out and the levels were a little different.

Also, when i calibrate the subwoofer, I get around -11 or -13 compared to the center's 0. Knob is about halfway up on the sub. I set the weight to "c" and response to slow while the rest of the speakers were tested with "a" weight and fast response. Am I doing it right? thanks.

Any form of calibration is to establish a baseline with a standard. "C" weighting on the spl meter is correct. The relative values of numbers and knobs are meaningless.

Bottom line is you can calibrate and then tweak to get the sound you want.

I would say the Avia calibration disc. The self calibrating receivers get you close, but using the SPL meter with disc is the best.

Have meter on "C" and "slow" for all speakers.............

Receiver first, disc second. The reason is that you want to calibrate with test tones to get a baseline for your receiver. This will help every input you might ever use, even radio. But DVD players or other sources can have an effect, also. So you want to check it with a disc in case the route from player to receiver is affecting something.