Caltrans Online Training-Highway Traffic Noise Fundamentals

What is sound? Sound is a vibratory disturbance in a gas, liquid, or solid that can be detected either naturally (by a human ear, for example) or artificially, such as by a microphone. It is a mechanical energy transferred from a vibrating object to a medium surrounding it, such as air and water. The medium, in turn, transmits the energy in the form of pressure waves to a receiver. Our focus in this course is sound energy that is transmitted through air, or airborne sound. Sound has physical characteristics that can readily be quantified. How sound is perceived, or qualified, is much more difficult. One person's music is another person's noise. Noise is defined as sound that is loud, unpleasant, unexpected, and undesired. Although the determination of what is noise and what is sound is purely subjective, most people will agree that sound from highway traffic is noise. Physically, sound and noise behave identically. For the purposes of this discussion, we may use the terms interchangeably. The study of sound requires the consideration of three essential components: the source, the path, and the receiver. Studying these three components together form the basic approach in any noise analysis.

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