What is low-frequency noise?
Low-frequency noise (LFN) is generally taken to mean noise below a frequency of about 100 to 150 hertz. The human ear is not very sensitive at these low frequencies. However, people living close to airports may experience LFN. They may experience LFN as a distant rumbling noise, structural vibration, or objects rattling in homes, at distances beyond “significant noise exposure areas.” These areas are designated as those having a “day/night” noise level of less than 65 decibels, or “DNL<65." (For aviation noise analysis, the FAA has determined that people’s cumulative aviation-related noise exposure is to be rated in terms of yearly day/night average sound level exposure. DNL takes into account both the number of events (takeoffs and landings) over a 24-hour period as well as the noise level of each event. To account for people’s heightened sensitivity to nighttime noise, one event between 10 p.m. and 7 a.m. equals 10 daytime events. The FAA considers a DNL of 65 decibels or greater as
