A SPL (Sound Pressure Level) meter is an important audio measurement tool. In live audio there are SPL restrictions in some indoor and outdoor venues which must be maintained. As a sound system is optimized, part of the optimization process is adjusting levels through out the entire system (including all sub systems) so that every seat in the venue has relatively even coverage.
There are various stand alone SPL meters ranging from expensive to very inexpensive. The more expensive models are calibrated at the factory and can be used for SPL certification purposes. The less expensive models provide an an certified SPL glimpse. There are even smart phone apps that take advantage of the built in mic to provide SPL levels. Lots of options these days.
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Rational Acoustics offers a complete SPL measurement system using Smaart 7, Smaart I-O, RTA-420 measurement mic with calibration file.
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In order to maintain a SPL meter it must be calibrated from time to time. In critical situation, it is standard practice to calibrate your SPL meter prior to each use. In order to calibrate an SPL meter, you need a calibrator device like this:
The following are articles about SPL and SPL measurement: