I just picked up a Radio Shack analog SPL meter and I have a few questions (and or problems). For example: When I set my meter to "A" weighting, I'll get a reading of roughly 60 db in my theater room. However, when I jump to "c" weighting, the needle will peg to the right. Why is there a large gap between A and C weightings on the meter? Also, when I switch to "c" weighting, and set the meter to 70db, I cannot calibrate at this level because the needle is pegged to the right. I can only calibrate at 85db. How can my quiet basement theater be reading over 75db with no test tones playing? Could there be a problem with the meter? Thanks for any help.