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Noise Metrics and Community Response 115
Figure 7-2. Comparative single event noise metrics compared to equivalent noise level.
while clearly accounting for both their peak noise levels and durations. For example, the same
operation may be considered along an existing and proposed flight track. The SEL of each oper-
ation would be compared to provide insight into the prospective effects of changing location
on the underlying population. Further, the SEL is the preferred metric for the evaluation of
sleep disturbance, making it critical to the evaluation of noise abatement measures that are
directed at night operations. Typically, the SEL is approximately 8-10 decibels louder than the
peak noise level that occurs during a single event. The SEL is represented by a series of dark bars
and compared to the measured noise levels, including Lmax, through the course of several single
events in Figure 7-2.
Example of Metric Display for Public Information:
· Example of SEL computation Video: (prepared for ACRP 02-05 project) 7-6
Maximum A-Weighted Sound Level (Lmax)
The Lmax of an event represents the loudest decibel level achieved during that event. It also can
be expressed over a period of time (hour, day, year, etc.). Similar to SEL, the metric is useful to
compare operational alternatives for noise abatement. Unlike SEL, it is not subject to the com-
pression of all noise energy during an event into a single second, but rather provides the instan-
taneous peak noise level achieved. Consequently, it is the loudest aircraft noise level the public
experiences, and often the one most cited in public comment and complaint.
Example of metric display for public information:
· Comparison of Sound Outdoor and Indoor sound levels (157) 7-7
· ORD Aircraft Noise Comparison (single event footprints) (158) 7-8
· Loudest Aircraft Noise Events Site Report (Chicago O'Hare) (159) 7-9
· Example of Lmax computation Video (prepared for ACRP 02-05 project) 7-10
