THE SCIENCE AND APPLICATIONS OF ACOUSTICS - H. H. Arnold ...

9Sound-Measuring Instrumentation9.1 IntroductionAcoustic measurements constitute an essential step in order to establish the status ofan acoustic environment and to develop a systematic approach toward modifyingthe environment and to set up criteria for improvements. Other more recentlydeveloped methodologies of acoustical measurements entail the studies of materialproperties and medical diagnoses. A wide variety of instrumentation exists, rangingfrom a simple sound pressure level (SPL) meter to real-time spectral analyzersinterfaced with sophisticated computer systems. Instruments may be portable forfield use; and recorded field data can be later evaluated in more elaborate systems.New instruments are continually being developed, and with new advances in digitaltechnology arriving on the scene on a daily basis, it is not inconceivable thatmore versatile and “user-friendly” devices will become available at even lowerprices.This chapter deals principally with instruments intended for the audio rangeof frequencies. Much of the salient aspects of instrumentation in this chapter,such as the principal performance requirements and methodologies for evaluatingdata, also apply to the specialized underwater instruments and ultrasonic sensinginstruments which are described in Chapters 15 and 16, respectively.9.2 Principal Characteristics of Acoustical InstrumentsThe most important performance characteristics of acoustical instruments are thefrequency response, dynamic range, crest factor capability, and response time. Itis also desirable that a measuring device or system has a negligible (or at leastpredictable) effect or influence on the variable being measured.Frequency response refers to the range of frequencies that an instrument is capableof correctly measuring the relative amplitudes of the subject variable withinacceptable limits of accuracy. Measurement accuracy depends on the instrumentationtype, the quality of design and manufacture, and calibration. A typical limit forthe flatness of the response for microphones may be ±2 dB or better; in contrast,173