when calibrating my subwoofer, should the volume gain on the sub be set to 1/2 or max? when i calibrate the sub with the rest of the system (the sub being at 1/2 gain) i have to leave the sub at +10 decibals so it reads 75 on my sound meter like the rest of my 5.1 system. does that sound right? +10decibals sounds kind of high being that the rest of the speakers are at +1,-1,0 etc. what do you guys think?

I've typically calibrated my sub with the gain on the sub set to around 1/2. +10dB is certainly a fairly high setting, but there's nothing wrong with it.

Is your meter set to A weighted, C weighted, or flat? The last time I saw something like that the meter was set to A weighted which approximates the non-linearity of the human ear at very low volumes.

C weighting approximates the non-linearity of the human ear at louder volumes. When shooting for 75dB you should use C weighting or flat response.

Both C and A weighting attenuate the bass somewhat inside the meter, but the A weighting attenuates it greatly.

It is also possible that the meter itself is not accurate at low frequencies. It requires a lot more processing to accurately measure low frequencies than mid and high frequencies. That is why Galaxy audio has several models rated for different frequency ranges, the 140 which is rated down to 31.5 hertz costs double what the 130 does, which is only accurate down to 125hz.