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Introduction to Acoustics

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1164 Detailed Contents<br />

Detailed Cont.<br />

23.3 Propagation Paths ........................................................ 991<br />

23.3.1 Sound Propagation Outdoors ................................. 991<br />

23.3.2 Sound Propagation Indoors ................................... 993<br />

23.3.3 Sound-Absorptive Materials .................................. 995<br />

23.3.4 Ducts and Silencers ............................................ 998<br />

23.4 Noise and the Receiver .................................................. 999<br />

23.4.1 Soundscapes ................................................... 999<br />

23.4.2 Noise Metrics ................................................... 1000<br />

23.4.3 Measurement of Immission Sound Pressure Level .......... 1000<br />

23.4.4 Criteria for Noise Immission .................................. 1000<br />

23.4.5 Sound Quality .................................................. 1004<br />

23.5 Regulations and Policy for Noise Control ............................... 1006<br />

23.5.1 United States Noise Policies and Regulations ............... 1006<br />

23.5.2 European Noise Policy and Regulations ..................... 1009<br />

23.6 Other Information Resources ............................................ 1010<br />

References ........................................................................ 1010<br />

Part H Engineering <strong>Acoustics</strong><br />

24 Microphones and Their Calibration<br />

George S. K. Wong ................................................................ 1021<br />

24.1 His<strong>to</strong>ric References on Condenser Microphones and Calibration ..... 1024<br />

24.2 Theory ..................................................................... 1024<br />

24.2.1 Diaphragm Deflection ......................................... 1024<br />

24.2.2 Open-Circuit Voltage and Electrical Transfer Impedance ... 1024<br />

24.2.3 Mechanical Response ......................................... 1025<br />

24.3 Reciprocity Pressure Calibration ......................................... 1026<br />

24.3.1 <strong>Introduction</strong> .................................................... 1026<br />

24.3.2 Theoretical Considerations .................................... 1026<br />

24.3.3 Practical Considerations ....................................... 1027<br />

24.4 Corrections ................................................................ 1029<br />

24.4.1 Heat Conduction Correction ................................... 1029<br />

24.4.2 Equivalent Volume ............................................ 1031<br />

24.4.3 Capillary Tube Correction ...................................... 1032<br />

24.4.4 Cylindrical Couplers and Wave-Motion Correction .......... 1034<br />

24.4.5 Barometric Pressure Correction ............................... 1035<br />

24.4.6 Temperature Correction ....................................... 1037<br />

24.4.7 Microphone Sensitivity Equations ............................ 1038<br />

24.4.8 Uncertainty on Pressure Sensitivity Level .................... 1038<br />

24.5 Free-Field Microphone Calibration ..................................... 1039<br />

24.6 Comparison Methods for Microphone Calibration ..................... 1039<br />

24.6.1 Interchange Microphone Method of Comparison ........... 1039<br />

24.6.2 Comparison Method with a Calibra<strong>to</strong>r ....................... 1040<br />

24.6.3 Comparison Pressure and Free-Field Calibrations .......... 1042<br />

24.6.4 Comparison Method with a Precision Attenua<strong>to</strong>r ........... 1042<br />

24.7 Frequency Response Measurement with Electrostatic Actua<strong>to</strong>rs ..... 1043

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