What is the best way to calibrate the SPL meter?

[RIppolito]

I have taken measurements over several days, and the levels do not seem consistent. I turn off the computer (MacBook Pro) between measurement sessions. After starting REW and checking that my preferences are good, I always check levels with the SPL meter. The results will vary as much as 5-8 dB on pink noise across boots, but are pretty consistent, measurement to measurement, after a start up. The waveform shapes across boots are very consistent for any given channel, but the levels are not. If I were to do a vector average of multiple measurements across boots, I believe the results would be inaccurate because of the variance in the levels.

I suspect the culprit is not having a calibrated SPL meter. Is there a recommended procedure to calibrate the SPL meter? Alternatively, is there a way to play the pink noise at a known level and tell the meter 'this is 70 dB'?

The only other device I have is an analog Radio Shack SPL meter, but it does not show digital values: it has a needle that sweeps from -10 dB to +6 or so.

Thank you, in advance, for any help you can provide...
Ron

 

[John Mulcahy]

You can use the Align SPL option to bring measurements into alignment before averaging.

Levels should be consistent unless either the input or output volume controls have been changed. Calibration shouldn't matter, but you can pick any not-too-loud test signal and use it to give the REW meter a calibration value using the Calibrate button on the REW SPL meter. To use the Radio Shack meter for the value to enter for SPL calibration the level is the needle reading plus the range setting - e.g. on the 80 dB range needle at -2 dB would be 78 dB.

 

[kpjamro]

You can buy a calibrator device for your SPL meter. These make 114 dB at 1 kHz and sometimes other levels like 94 or 104 dB. Cost is 100 USD and upwards.