Having an interesting problem doing the room calibration...

I have a digital Radio Shack SPL meter we've had for a while. I keep it in the box with the battery out since I only use it for changes in the system and don't want it to leak and ruin the meter.

Hooked everything up, found the specs on the meter in the manual (1 V) and ran the room correction. It says the levels are too low (2 dB) and it needs 18 dB. Set the meter according to the manual (C weighting, 90 dB range since I could only get 73 dB when doing speaker calibration).

We tried a Shure mic just to see what it would do... even worse results.

I have tried 3 different cables as well... I know it isn't "required" but I would LIKE to have it dialed into the room if possible.

Ideas?

G68D, DSP7000's, DSP5000C (18 bit), DSP420's, MF-1 Projector, Sony XBR-65 4K