Letter: Aircraft noise comparison is faulty

Re: the April 4 article "D-M neighbors ask judge to order full impact study of flight noise"

Reporter Howard Fisher wrote that 70-decibel aircraft noise is the same as the noise of a vacuum cleaner.

In fact, they are not the same. Vacuum-cleaner noise, and most other noise, is measured by a method known as SEL, which records the sound we actually hear. The Air Force measures aircraft noise with a method known as DNL, which averages noise over 365 days.

To compare a vacuum cleaner to an aircraft, you must convert the vacuum cleaner’s noise to DNL decibels. To do this, you average (for example) 20 minutes of its running at 70 decibels with 23 hours and 40 minutes of its sitting at zero decibels in a closet. You then project this through 365 days.

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Sound ridiculous? It is. But that’s how the Air Force measures aircraft noise.

Gary Hunter

Midtown