NOISE MEASUREMENT
SOUND METRICS
Purpose
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Multiple metrics are used to describe sounds. This introduces the ones most important in airport noise management. | |
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Five different metrics describing the same sound can be selected: Current level, Lmax, LEQ, SEL, and Time Above. There are also five different sounds, each with its own set of descriptors. Metrics and sounds are selected by clicking on the appropriate buttons. Clicking on the speaker icon at the lower right will play the selected sound as will clicking on the current level display. |
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There are various animations associated with the different metrics. LEQ shows levels being "energy averaged" and SEL shows levels being compressed into a single second. The Time Above display has a slider that permits adjusting the threshold level. The resulting "time" is reported both as a graphic and as a numeric value. It is possible to shift the entire histogram upward or downward by adjusting the slider that appears when the Lmax value is selected. This might be used to set several sounds to a common level of SEL or LEQ and to play the resulting sounds. This section of the program explains how 24-hour metrics are constructed and what they signify in terms of annoyance. People relate to individual noise events more easily than 24-hour summations. The challenge here is to present the case for cumulative metrics such as DNL. | |
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