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JCC Tri-Vatey Preschool Outdoor Play Area Noise 30 January 2017 Page 7 activities such as single vehicle pass-bys,aircraft flyovers,etc.which cause the environmental noise level to vary from instant to instant. To describe the time-varying character of environmental noise,statistical noise descriptors were developed."L10"is the A-weighted sound level equaled or exceeded during 10 percent of a stated time period.The L10 is considered a good measure of the maximum sound levels caused by discrete noise events. "L50"is the A-weighted sound level that is equaled or exceeded 50 percent of a stated time period; it represents the median sound level.The"190"is the A-weighted sound level equaled or exceeded during 90 percent of a stated time period and is used to describe the background noise. As it is often cumbersome to quantify the noise environment with a set of statistical descriptors,a single number called the average sound level or"Le"is now widely used.The term"Leq"originated from the concept of a so-called equivalent sound level which contains the same acoustical energy as a varying sound level during the same time period. In simple but accurate technical language,the Leg is the average A-weighted sound level in a stated time period.The Leg is particularly useful in describing the subjective change in an environment where the source of noise remains the same but there is change in the level of activity.Widening roads and/or increasing traffic are examples of this kind of situation. In determining the daily measure of environmental noise, it is important to account for the different response of people to daytime and nighttime noise. During the nighttime,exterior background noise levels are generally tower than in the daytime; however, most household noise also decreases at night, thus exterior noise intrusions again become noticeable. Further,most people trying to sle.43 at night are more sensitive to noise.To account for human sensitivity to nighttime noise levels,a special descriptor was developed.The descriptor is called the DNL or Len(Day/Night Average Sound Level), which represents the 24-hour average sound level with a penalty for noise occurring at night.The La" computation divides the 24-hour day into two periods: daytime(7:00 am to 10:00 pm); and nighttime (10:00 pm to 7:00 am).The nighttime sound levels are assigned a 10 dB penalty prior to averaging with daytime hourly sound levels. For highway noise environments,the average noise level during the peak hour traffic volume is approximately equal to the Lan. The effects of noise on people can be listed in three general categories: • Subjective effects of annoyance, nuisance,dissatisfaction Acoustics • Interference with activities such as speech,sleep,and learning Audio+risual • Physiological effects such as startle, hearing loss Telecommunications Security The sound levels associated with environmental noise usually produce effects only in the first two categories. Unfortunately,there has never been a completely predictable measure for the subjective effects of noise nor of the corresponding reactions of annoyance and dissatisfaction.This is primarily because of the wide variation in individual thresholds of annoyance and habituation to noise over time. 130 Sutter Street F"er5 Sc,Franaico CA Thus,an important factor in assessing a person's subjective reaction is to compare the new noise 94104 environment to the existing noise environment. In general,the more a new noise exceeds the existing, t 4 1 5 3970442 the less acceptable the new noise will be judged. F 415 3970454 .v.Y.'crnvo!!e,corn -1111111111 minsurf Salter a ori;„rF nu'