FAQ - What Are The Units Of Measurement For Airplane Noise

Question: What are the units of measurement for airplane noise?

Answer: The full, audible frequency range for healthy ears extends from about 20 Hz (cycle per second) to about 20,000 Hz. However, the human hearing mechanism is most sensitive to sound in the 500- to 8,000-Hz range. Above and below this range, the ear is inherently less sensitive. To account for the varying sensitivity of the normal human ear to sound over the audible frequency range, sound level meters incorporate an electronic filter (or weighting network) that approximates the way the human ear perceives sound over the audible frequency range. Sound level values obtained using the weighting network are referred to as ?A-weighted? sound levels and are signified by the identifying unit, dBA. The full dynamic range of human hearing covers from about 20dBA (quiet recording studio) up to levels of 130 dBA (sensation of pain). Normal conversation level is at about 60 dBA. Typical noise levels due to auto traffic on a busy street are in the range between 65 to 75dBA. Typical noise levels due to flying airplanes over Foster City vary from about 55 to 85 dBA, depending on the location, the type of airplane and the flyover altitude. The ?A? weighted dBA level is a descriptor for an individual noise event.

A unit of measurement that reflects the cumulative effects of individuals events over a period of time, say a 24 hour day, as would be experienced by a community is the so-called day night level (LDN), and is called in California the CNEL (community noise exposure level). This LDN or CNEL unit was devised to give a quantitative indication of the collective exposure to noise often from many sources of different strengths in a community over a period of time.


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