You could look at Speaker Workshop. It is a full-fledged measurement system that you could use to make response graphs. But it would have to be calibrated to give you an accurate SPL, and the only way you could do that is to use the Radio Shack meter as a reference. Not my idea of a golden reference, but the price is right.You might also consider purchasing a measurement system like LMS, which comes with a calibrated microphone and has built-in calibration functions for the rest of the system. That would give you confidence in the accuracy of your SPL charts.