For almost everyone, every acoustic measurement session begins by calibrating or entering the acoustic sensitivity of their measurement microphone(s), typically expressed in mV/Pa, into their analysis system. Using a sound level calibrator, such as the GRAS 42AG pictured below, you can capture the sensitivity of the measurement microphone(s) you are using so that you ultimately capture accurate results for the device under test (DUT) you are characterizing. However, what if there was another way? What if it was possible to electronically read the microphone sensitivity directly from the sensor and into the analysis software for use in any acoustic measurement?
GRAS 42AG multifunction sound calibrator
TEDS–the Transducer Electronic Data Sheet—is a method, defined by IEEE 1451, of storing the microphone’s (i.e., transducer’s) sensitivity information on a chip inside the preamplifier. Combing APx500 software and appropriate interface hardware, such as the APx517B Acoustic Audio Analyzer or the GRAS 12BA or 12BB CCP power modules, makes this possible.
Audio Precision APx517B Acoustic Analyzer
GRAS 12BB CCP Power Module
Instead of starting every measurement session by spending anywhere from 15 minutes to an hour or more calibrating each microphone you are using, you can, at the click of button, read the microphone’s sensitivity directly into the APx measurement software. APx500 can even be configured so that at the start of each test sequence the sensitivity is automatically read. So, in the case where microphones are moved around between test sessions, the data for the microphone used at that moment is always automatically read into the software.
While reading TEDS data instead of calibrating a microphone each time it is used can be vastly more convenient, it is important to recognize a few limitations. First, the TEDS data is only as good as when it was originally written. For many microphones this is when it was originally calibrated at the factory. Second, the TEDS data cannot account for any signal amplification or attenuation between the microphone and the analyzer. For these reasons it remains good practice to periodically calibrate microphones with an acoustic calibrator to verify the TEDS data against an actual sensitivity reference.
Reading TEDS data and setting measurement microphone sensitivity within APx500 audio measurement software. (click to enlarge)
As an added benefit, reading and applying measurement mic sensitivity data to measurements can be automated, saving additional time in the overall measurement process, whether on the manufacturing line or in the lab.