Introduction

People are exposed to noise during daytime and nighttime hours. During the day the noise can interfere with various activities and cause annoyance, and at night it can affect sleep. Very intense noise can even lead to hearing damage (see Chapter 4). In the daytime the activities most affected are communications that involve speech between individuals, speech in telephone communications, and speech and music on radio and television. If the noise is more intense, it is normally more annoying, although there are a number of other attitudinal and environmental factors that also affect annoyance.

There are many different ways to measure and evaluate noise, each normally resulting in a different noise measure, descriptor, or scale. The various measures and descriptors mainly result from the different sources (aircraft, traffic, construction, industry, etc.) and the different researchers involved in producing them. From these measures and descriptors, criteria have been developed to decide on the acceptability of the noise levels for different activities. These criteria are useful in determining whether noise control efforts are warranted to improve speech communication, reduce annoyance, and lessen sleep interference. This chapter contains a review and discussion of some of the most important noise measures and descriptors. In the past 20–30 years these measures and descriptors have undergone some evolution and change as researchers have attempted to find descriptors that best relate to different human responses and are more easily measurable with improved instrumentation. For completeness this evolution is traced and some measures and descriptors are described that are no longer in use, since knowledge of them is needed in the study of the results of various noise studies reported in the literature.