To solve a noise problem, one must find out something about what the noise is doing, where it comes from, how it travels, and what can be done about it. A straightforward approach is to examine the problem in terms of its three basic elements; that is, sound arises from a source, travels over a path, and affects a receiver or listener.
The source can be one or any number of mechanical devices that radiate noise or vibratory energy. Such a situation occurs when several machines are operating at the same time.
The most obvious transmission path by which noise travels is a direct line-of-sight air path between the source and the listener. For example, aircraft flyover noise reaches an observer on the ground by the direct line-of-sight air path.
Noise also travels along structural paths. Noise can travel from one point to another via any one path or a combination of several paths. Noise from a washing machine operating in one apartment can be transmitted to another apartment along air passages such as open windows, doorways, corridors, or duct work. Direct physical contact of the washing machine with the floor or walls sets these building components into vibration. This vibration is transmitted structurally throughout the building causing walls in other areas to vibrate and to radiate noise.
The receiver may be, for example, a single person, or a suburban community.
The solution of a noise problem requires alteration or modification of any or all of the following three basic elements:
• Modifying the source to reduce its noise output
• Altering or controlling the transmission path and the environment to reduce the noise level reaching the listener
• Providing the receiver with personal protective equipment
Modifying the source to reduce noise output involves noise-level specifications, process substitution, machines substitution, and systems design.
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