How Loud is the Noise? 

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PEAK NOISE

Peak noise levels, in decibels (dB) are what we hear. Peaks startle us, wake us, and register on the noise meters that some of us might use to determine the loudness of an airplane. Peak noise for an event, like a gunshot, may last for only a fraction of a second.

SENEL

Single Event Noise Exposure Levels, also expressed in dB, are calculated values. The energy from a noise event, like an aircraft overflight, is expressed as if it all occurred during a one-second long event. Since the sound energy of an aircraft overflight may last for 30-40 seconds, compressing it into just one second results in a calculated SENEL value that is usually about 8-10 dB greater than the actual peak noise level.

CNEL

Most published information from the County, regarding noise for the El Toro Reuse project, is given in a third measure: as Community Noise Equivalent Levels (CNEL).  The CNEL is a calculated average over a 24 hour period.  Because it is a calculation, based on a mixture of noises, it is not possible to hear what 65 CNEL sounds like.

A deafening explosion, on an otherwise quiet day, will yield a low CNEL calculation due to the averaging.  Night time noises are "penalized" by 5 or 10 db in the CNEL calculations.

The County of Orange Environmental Impact Report takes the position that a 65 db CNEL does not impose a significant adverse impact, even though it may include repeated short bursts of very loud noise.

Click here for  "Putting 65 dB CNEL in Perspective"

The following is Table B.1 from Federal Agency Review of Selected Airport Noise Analysis Issues [page B-6] published by the Federal Interagency Committee on Noise (August 1992) Source of the information is attributed to a publication titled Outdoor Noise and the Metropolitan Environment by M.C. Branch, et al. Los Angeles California: Department of City Planning, City of Los Angeles, 1970

Table B.1 Sound levels (dB) and relative loudness of typical noise sources in indoor and outdoor environments
 

dB(A)	Overall Level	Community Noise Levels (Outdoors)	Home and Industry Noise Levels	Subjective Loudness (Relative to 70 dB)
120	Uncomfortably Loud	Military jet aircraft take-off from aircraft carrier with afterburner at 50 ft . . . 130 dB	Oxygen Torch . . . 121 dB	32 times as loud
110		Turbo-fan aircraft at takeoff power at 200 ft . . . 118 dB	Riveting machine . . . 110 dB  Rock band . . . 108 - 114 dB	16 times as loud
100	Very loud	Boeing 707 or DC-8 aircraft at one nautical mile (6080 ft) before landing . . . 106 dB  Jet flyover at 1000 feet . . . 103 dB  Bell J-2A helicopter at 100 ft . . . 100 dB		8 times as loud
90		Boeing 737 or DC-9 aircraft at one nautical mile (6080 ft) before landing . . . 97 dB  Power mower . . . 96 dB  Motorcycle at 25 ft . . . 90 dB	Newspaper press . . . 97 dB	4 times as loud
80		Car wash at 20 ft . . . 89 dB  Propeller plane flyover at 1000 ft . . . 88 dB  Diesel truck 40 mph at 50 ft . . . 84 dB  Diesel train 45 mph at 100 ft . . . 83 dB	Food blender . . . 88 dB  Milling machine . . . 85 dB  Garbage disposal . . . 80 dB	2 times as loud
70	Moderately loud	High urban ambient sound . . . 80 dB  Passenger car 65 mph at 25 ft . . . 77 dB  Freeway at 50 ft from pavement edge 10 a.m. . . . 76 dB	Living room music . . . 76 dB  Radio or TV-audio. vacuum cleaner . . . 70 dB	70 dB(A)
60		Air conditioning unit at 100 ft . . . 60 dB	Cash register at 10 ft . . . 65-70 dB  Electric typewriter at 10 ft . . . 64 dB  Dishwasher (Rinse) at 10 ft . . . 60 dB  Conversation . . . 60 dB	1/2 as loud
50	Quiet	Large transformers at 100 ft . . . 50 dB		1/4 as loud
40		Bird calls . . . 44 dB  Lowest limit of urban ambient sound . . . 40 dB
10		Just audible
0		Threshold of Hearing