Need some help on the SPL calculations on my radio shack meter. I just measured my room response. I baselined at 80dB for 1000Hz to get 0 on the meter using the Rives CD2 calibrated test tones. When I measured the SPL of the 25 Hz tone I have to change the meter to 90 and it reads -4dB does this means it is (80dB-4db+10dB)=86db? Likewise at 12.5kHz, I changed the meter to 70dB and it reads -6dB does this mean it is (80dB-6db-10db)=64db? Just want make sure I am interpreting correctly - would like to post the data and get some responses.
When you change the scale on the RS meter, the reading is correct without any adjustment. So, in your case, when the meter scale is 90bd, and it reads -4db, the sound pressure is 86db. This is the same way a voltmeter works when changing scales.