In the calibration of a Working Standard Microphone (WSM), in addition to sensitivity calibration, one of the most important characteristics is its frequency response. Since every microphone exhibits different sensitivity across the frequency range, verifying and documenting the frequency response is essential to ensure that acoustic measurements in practical applications are accurate and comparable according to international standards such as IEC 61094-6.
Use of an Electrostatic Actuator
An actuator is a device that generates a simulated acoustic field, either in the form of a pressure field or coupler field, to excite the WSM at specified frequencies. The actuator is typically used in conjunction with a signal generator to compare the response of the microphone under test (UUT: Unit Under Test) against a reference signal.
Principle of Operation of the Electrostatic Actuator
- An electrical signal from the signal generator is supplied to the actuator driver.
- Inside the coupler chamber, a corresponding acoustic pressure field is generated at the specified frequency.
- The Working Standard Microphone (WSM) measures this acoustic pressure and compares it with a reference microphone that has traceability to the National Metrology Institute (NMI).
- The measured data are then plotted as the frequency response curve of the WSM.
Calibration of the frequency response of a microphone using an electrostatic actuator is therefore a crucial step in the quality assurance of acoustic measurements. This is particularly significant for the Working Standard Microphone (WSM), which is designed and manufactured in compliance with IEC 61094-4 to serve as a secondary standard for the calibration of other microphones.
The information obtained from frequency response calibration is compared between the WSM and a reference microphone that has been calibrated according to international standards. This process systematically verifies the accuracy, stability, and consistency of the WSM. Once confirmed, the WSM can be reliably used as a secondary standard for calibrating general-purpose microphones employed in sound level meters, as well as in environmental, industrial, and research applications.
Conclusion
The use of an electrostatic actuator in frequency response calibration not only enhances the accuracy of microphone calibration but also reinforces confidence in the traceability chain of acoustic metrology. This ensures that measurement results are internationally recognized and comparable.