Measurement microphones are, of course, designed to take measurements with scientific accuracy. In the same way that you wouldn’t use a microscope without first calibrating it, the same applies to the microphone equipment you’re using too.
What is calibration?
Simply put, calibration is the fine tuning to the set up of your equipment to maximise performance and accuracy of output. Just as Formula One engineers will calibrate their tyre pressures for optimal grip and durability, by calibrating your microphones and equipment, you can ensure consistent performance and measurements.
Reciprocity Calibration is the most common, and internationally recognised method of calibrating measurement microphones. This technique uses laboratory calibrated microphones to test and calibrate other microphones using, effectively, comparison calibration. There are international standards for this technique giving you the knowledge that your calibration is completed to a certified standard.
Why should I calibrate anyway?
Like most devices, audio, laboratory, or otherwise, the more you use a piece of equipment, it will change. Even without use, there will be variances. Think of a guitar, for example, just sitting on its stand it strings will change their tuning simply with the change of temperature.
With changes to the capsule inside the microphone, even minor ones, taking place, you are no longer guaranteed an accurate measurement and, therefore, accurate results. Assuming you’re using your microphones to measure the output of speakers, this isn’t such a problem. If, however, you’re testing the ground around an active volcano, you’d hope that the equipment is well calibrated!
As we mentioned, there are international standards of calibration, and the calibration of your devices should be traceable to the primary standards provided by labs which rely on the International Laboratory Accreditation Association. These include the National Physical Laboratory in the UK, PBT in Germany, and NIST in the United States.
Many of the companies that supply measurement microphones also provide ongoing calibration services too, which will also conform to the international standards of calibration. This means that you can trust that your supplier or manufacturer will also assist you in the maintenance and upkeep of your microphones.
A microphone’s sensitivity varies with frequency, along with other factors such as as environmental conditions. Calibration, therefore, is normally recorded in different sensitivity values for each specific frequency. The sensitivity of the microphone can also depend on the nature of the sound field it is exposed to. For this reason, microphones are often calibrated in more than one sound field, for example a pressure field and a free field. Depending on their application, measurement microphones must be tested periodically (every year or several months, typically), and after any potentially damaging event, such as being dropped or exposed to sound levels beyond the device’s operational range.
With a range of microphones available to you, including free-field and pressure microphones, GRAS.dk is a leading provider in acoustic measurement devices. Supplying industries from aerospace and automotive to audiology and consumer electronics, GRAS has the experience and knowledge to provide true excellence of standards. With their in-house calibration services too, you can also be assured of consistent quality.