Gateway Engineering Coalition Home Page   Principal Characteristics of

Acoustical Instruments

The most important performance characteristics of acoustical instruments are the frequency response, dynamic range, crest factor capability, and response time. It is also desirable that a measuring device or system have a negligible (or at least predictable) effect or influence on the variable being measured.


Frequency response refers to the range of frequencies which an instrument is capable of correctly measuring the relative amplitudes of the subject variable within acceptable limits of accuracy. Measurement accuracy depends on the instrumentation type and the quality of design and manufacture. A typical limit for the flatness of response for microphones may be 2 dB or better; in contrast, the response curve of a high quality loudspeaker' may deviate 5 dB over its rated frequency range.


Dynamic range defines the range of signal amplitudes an instrument is capable of handling in the process of responding and measuring accurately. A sound level meter, for example, that can measure a minimum of 10 dB and a maximum of 150 dB, is said to cover a dynamic range of 140 dB.


Crest factor capability denotes an instrument's capacity to measure and distinguish instantaneous peaks. Crest factor itself is the ratio of the instantaneous peak sound pressure to the root-mean-square sound pressure.


Response time refers to the rapidity a measuring instrument responds to rapid changes in signals. An oscilloscope display of a square wave response will result in a trapezoidal display if the relayed signals came from a loudspeaker that requires a longer reaction time to respond to a square-wave pulse.


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Support for the development of this module was provided by the National Science Foundation and The Cooper Union for the Advancement of Science and Art.

Please send questions or comments to Professor Ron Adrezin or Professor Daniel Raichel.