New Measurement Service for Determining Pressure Sensitivity of Type LS2aP Microphones by the Reciprocity Method

Area of Science:

• Acoustics and metrology
• Electrical engineering and acoustics

Background:

• The National Institute of Standards and Technology (NIST) provides essential calibration services for scientific instruments.
• Accurate pressure sensitivity measurements are critical for laboratory standard microphones used in various acoustic applications.

Purpose of the Study:

• To introduce a new NIST measurement service for determining the pressure sensitivities of American National Standards Institute (ANSI) and International Electrotechnical Commission (IEC) type LS2aP laboratory standard microphones.
• To improve the accuracy and reduce the uncertainty of these measurements compared to previous services.

Main Methods:

• Utilized an improved system based on NIST's participation in the Consultative Committee for Acoustics, Ultrasound, and Vibration (CCAUV) key comparison CCAUV.A-K3.
• Employed both long and short air-filled plane-wave couplers for measurements across the frequency range of 31.5 Hz to 20,000 Hz.
• Averaged data from both couplers for frequencies up to 2000 Hz, and used only the short coupler for frequencies above 2000 Hz.

Main Results:

• The new service achieves expanded uncertainties that are at most half the values of the previous service across most common frequencies.
• Proof test data demonstrated that average absolute differences between the long and short couplers were substantially smaller than the expanded uncertainties in the 31.5 Hz to 2000 Hz range.

Conclusions:

• The new NIST measurement service provides a significant advancement in the precise determination of microphone pressure sensitivity.
• The enhanced accuracy and reduced uncertainty benefit the calibration and performance verification of standard laboratory microphones.