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Summary of Key Points <br />Minnesota's noise pollution rules are based on statistical calculations that quantify noise levels according to <br />duration over a one-hour monitoring period. The L10 calculation is the noise level that is exceeded for <br />10 percent, or six minutes, of the hour, and the L50 calculation is the noise level exceeded for 50 percent, or 30 <br />minutes, of the hour. There is not a limit on maximum noise. <br />The statutory limits for a residential location are L10 = 65 dBA and L50 = 60 dBA during the daytime <br />(7:00 a.m —10:00 p.m.) and L10 = 55 dBA and L50 = 50 dBA during the nighttime (10:00 p.m. — 7:00 a.m.) <br />(Minn. State Noise Pollution Control Rules 7030.0040). This means that during the one-hour period of <br />monitoring, daytime noise levels cannot exceed 65 dBA for more than 10 percent of the time, and cannot <br />exceed 60 dBA more than 50 percent of the time. <br />Decibel levels of common noise sources <br />• <br />140 ---------------------------------- <br />Jet Engine (at 25 meters) <br />130 ---------------------------------- <br />Jet Aircraft (at 100 meters) <br />120 ---------------------------------- <br />Rock Concert <br />110 --- ------------------------------- <br />Pneumatic Chipper <br />100 ---------------------------------- <br />Jackhammer (at one meter) <br />90 ----------------------------------- <br />Chainsaw, Lawn Mower (at one meter) <br />M ----------------------------------- <br />Heavy Truck Traffic <br />70 ----------------------------------- <br />Business Office, Vacuum Cleaner <br />60 ----------------------------------- <br />Conversational Speech, Typical TV Volume <br />50 ----------------------------------- <br />Library <br />40 ----------------------------------- <br />Bedroom <br />30 ----------------------------------- <br />Secluded Woods <br />20 ----------------------------------- <br />Distance attenuation <br />Whisper <br />When the distance is doubled from a point source, such as a building, the sound level decreases by six decibels. <br />Example: 50 feet <br />= 60 decibels <br />100 feet = 54 decibels <br />200 feet = 48 decibels <br />When the distance is doubled from a line source, like a busy roadway, the sound level decreases by three <br />decibels. <br />Example: 50 feet = 70 decibels <br />100 feet = 67 decibels <br />200 feet = 64 decibels <br />Addition and subtraction of sources <br />A doubling of energy, or doubling of identical sources, yields an increase of three decibels. <br />Example: 85 decibels -+- 85 decibels = 88 decibels <br />Change in decibel level and perceived change in loudness <br />=b 1 dBA.......................... <br />Not Noticeable <br />f 3 dBA.......................... <br />Threshold of Perception <br />5 dBA.......................... <br />Noticeable Change <br />zL 10 dBA........................ <br />Twice (Half) As Loud <br />t 20 dBA........................ <br />Four Times (One Fourth) As Loud <br />Monitoring guidelines <br />The noise source being measured should be at least 10 dBA above the background noise level. <br />Keep at least as far away from any large reflecting object as from the source being measured. If this is not <br />possible, stay at least 30 feet from structures. <br />All measurements should be made with the microphone at lease three feet above the ground, in relatively calm <br />weather. 0 <br />A Guide to Noise Control in <br />Minnesota • October 2008 Minnesota Pollution Control Agency <br />