How It Works: Laser-Based Microphone Calibration (VIDEO)
Caption
A microphone works by converting pressure waves, or sound, into an electrical signal. NIST researchers have recently made what may be the first successful demonstration of a technique for performing this calibration with laser light. Laser light is bounced off the membrane surface. When the membrane is moving inwards, the frequency of the reflected light will be lower. Conversely, when the membrane is moving outwards, the frequency of the reflected light will be higher. The measurement allows researchers to extract information about the diaphragm's velocity, which is then compared to the electrical input of the microphone. By repeating this laser test with a "reference" microphone -- one that has been previously calibrated -- researchers can more accurately and easily calibrate microphones than they could with more traditional methods.
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S. Kelley/NIST
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