This is posted in "tech talk" maybe it will help you
Radio Shack SPL Meter mods corrections
I know that others here were interested in the specs to correct the non-linearities of the factory stock RS SPL meter. The figures below are to be either added to (+) or subtracted from (-) the readings that you obtain from your factory stock meter. In other words, the meter in stock form is EXTREMELY deficient when it comes to taking low frequency measurements. Keep in mind that these corrections are only valid under the following conditions. The meter must be set to C weighting, using 1/3 octave pink noise (easily available from various CDs), with the mic pointed at the speaker. These measurements were verified on both the RS analogue and digital meters using laboratory grade test equipment. Baseline testing was done using the 80 dB scale for reference purposes. While on the low side, this should give you a good baseline as to what your actually getting out of your system. Needless to say, if you had BIG peaks in the bass region with the stock meter and you weren't calculating in these correction figures, you're in even worse shape than you thought.
10Hz +20.5
12.5Hz +16.5
16Hz +11.5
20Hz +7.5
25Hz +5
31.5Hz +3
40Hz +2.5
50Hz +1.5
63Hz +1.5
80Hz +1.5
100Hz +2
125Hz +0.5
160Hz -0.5
200Hz -0.5
250Hz +0.5
315Hz -0.5
400Hz 0
500Hz -0.5
630Hz 0
800Hz 0
1KHz 0
1.25Khz 0
1.6KHz -0.5
2Khz -1.5
2.5Khz -1.5
3.15Khz -1.5
4KHz -2
5KHz -2
6.3KHz -2
8KHz -2
10Khz -1
12.5KHz +0.5
16KHz 0
20KHz +1
Radio Shack SPL Meter mods corrections
I know that others here were interested in the specs to correct the non-linearities of the factory stock RS SPL meter. The figures below are to be either added to (+) or subtracted from (-) the readings that you obtain from your factory stock meter. In other words, the meter in stock form is EXTREMELY deficient when it comes to taking low frequency measurements. Keep in mind that these corrections are only valid under the following conditions. The meter must be set to C weighting, using 1/3 octave pink noise (easily available from various CDs), with the mic pointed at the speaker. These measurements were verified on both the RS analogue and digital meters using laboratory grade test equipment. Baseline testing was done using the 80 dB scale for reference purposes. While on the low side, this should give you a good baseline as to what your actually getting out of your system. Needless to say, if you had BIG peaks in the bass region with the stock meter and you weren't calculating in these correction figures, you're in even worse shape than you thought.
10Hz +20.5
12.5Hz +16.5
16Hz +11.5
20Hz +7.5
25Hz +5
31.5Hz +3
40Hz +2.5
50Hz +1.5
63Hz +1.5
80Hz +1.5
100Hz +2
125Hz +0.5
160Hz -0.5
200Hz -0.5
250Hz +0.5
315Hz -0.5
400Hz 0
500Hz -0.5
630Hz 0
800Hz 0
1KHz 0
1.25Khz 0
1.6KHz -0.5
2Khz -1.5
2.5Khz -1.5
3.15Khz -1.5
4KHz -2
5KHz -2
6.3KHz -2
8KHz -2
10Khz -1
12.5KHz +0.5
16KHz 0
20KHz +1