Sound can be defined as atmospheric or airborne vibration perceptible to the ear. Noise is usually unwanted or undesired sound. Consequently, a particular sound can be noise to one person and not to others, or noise at one time and not at other times. Sound loud enough to be harmful is called noise without regard to its other characteristics. Noise is a form of pollution because it can cause hearing impairment and psychological stress.
This section introduces the subject of sound in engineering terms and includes appended references which provide detailed back-up material. It includes the general principles of sound production and propagation, a description of the ear and its functions, a description of the effects of noise on the hearing apparatus and on the person, and an introduction to hearing measurement and hearing aids.
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