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Another new area of study not addressed in the original 1985 document is low-frequency noise (LFN). LFN represents a special issue because outdoor A-weighted noise measurements may not appropriately reflect LFN levels that can induce potentially annoying secondary emissions inside residences near runways where the jet noise at the start of take-off roll and/or the jet noise from thrust reversers may cause LFN levels that are not typical of other areas in the airport environs. LFN is not absorbed by the atmosphere or blocked by terrain and buildings as well as higher frequencies. Therefore, LFN can sometimes be audible at farther distances than higher frequency noise. LFN has been studied at a small number of airports where community concern has been acute. The general conclusion from these studies is that LFN can induce structural building response that may cause rattle of windows, fixtures, pictures, and the like, causing annoyance well beyond the annoyance expected based on noise level alone. An Expert Panel con- vened by the communities around the MinneapolisâSt. Paul 18 International Airport produced a controversial report of which FICAN was highly critical that described a new noise metric and dose-response relationship for LFN (FICAN on the Findings . . . 2002). At the present time there is no universally accepted method of describing LFN and its impact on communities around airports. Some efforts to use the C-weighting for this purpose have been noted; however, this approach represents a poor surrogate for making octave or one-third octave measurements at the lower frequencies because the C-weighting will include sounds in frequencies above those that induce rattle. Current studies done under the Partner/COE (Center of Excellence) programs under sponsorship of the FAA and NASA shed more light on the levels of low-frequency sound needed to induce rattle effects. The results remain controver- sial. The results of the Partner/COE Project 1 low-frequency noise study were released in April 2007 (Partnership for AiR Transportation Noise & Emissions Reduction 2007). CHAPTER EIGHT AVIATION LOW-FREQUENCY NOISE AND VIBRATION
