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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