1004 59TH PL SW 2016-01-01 MF Import

Noise Assessment: Broadway Apartment'; Project Page 8 Michael R. Yantis Associates Inc., P.S. APPENDIX I: GENERAL DISCUSSION OF NOISE Environmental noise typically refers to the total acoustic environment as measured or heard by humans. This acoustic environment is made up of backvround noise caused by distant traffic, airplanes, etc., and higher level noise dominated by rearby sources such) as car pass-bys, airplane flyovers, or close construction activity. The most commonly used measure of sound is the sound pressure level (SPL), which represents the magnitude of the sound pressure in the air. The human ear responds differently to sounds at different frequencies (pitch). This is demonstrated by the fact that we hear higher pitched sounds easier than lower ones of the same magnitude. To compensate for the different "loudness" as perceived by humans at different pitches, a standard weighting curve is applied to measured levels. This weighting curve represents the human ear's sensitivity, and is labeled "A" weighting. The units of magnitude of the sound are written dBA ("A" weighted decibels), w nich is a logarithmic scale. The nature of dB scales means that individual dB ratings for different noise sources cannot be added directly to give the dB rating of the combination of these sources. Two noise sources producing equal dB rating at a Riven location will produce a co:nposite noise that is 3 dB greater than the individual levels. Similarly, the loud less of sounds does not vary arithmetically. The ear has some difficulty detecting the difference in loudness between sounds that have a difference of 3 dB. A 5 dB difference is easily detectable, and a sound that is 10 dB more than another sounds twice as loud. The following table presents examples of common noise levels: SPl.dBW r.smrle 0 Thmshold or audibility 20 Quiet rural area(no t"Mc) 40 Suburb neighborhood(d4tant traffic) 60 Normal con�crsation 70 Busy rreersy 100 Jackhammer 170 Thrr,hnld or pain Annoyance of environmental noise is further affected by the maximum (peak) levels, and the amount of Fluctuation of the noise. These factors can be described statistically by noise levels exceeded for given percentages of time during a prescribed time period. The statistical descriptors are L(1), L(10), L(50), L(90), and L(99), and represent the sound that is exceeded the percentage of time in parentheses. For example, L(50) is the sound level exceed 50% of the time in a given time interval. L(I) levels generally represent maximum levels, L(50) avem, ge levels, and L(99) background levels.