John J. Earshen
Angevine Acoust. Consultants, Inc., 1021 Maple St., P.O. Box 725, East Aurora, NY 14052-0725
A number of different metrics are in use for measuring and reporting exposure to noise for hearing conservation including noise dose, time-weighted average level, sound exposure, and sound exposure level. Functions for computation of individual metrics from measurement of acoustic pressure vary widely. Functions defining particular metrics in some instances contain choices of parameters (e.g., exchange rates and threshold levels). In most instances, once a metric has been evaluated for a particular time profile of acoustic pressure, it is not possible to convert it to another metric if the original time function is not retained. In addition to the defining functions, dynamic and frequency response characteristics of measuring instruments have influences on results obtained and can present obstacles to conversion among metrics. Large bodies of data exist which only contain the finally processed metric. The degree to which comparisons can be made because of recent changes in TLV requires inferential interpretation of the values of specific metrics which are produced by time functions that are identified only in a statistical sense. This paper examines the inferential relationships among prominent metrics for various classes of sound-pressure profiles as obtained with measuring instruments meeting ANSI and IEC performance standards.