# Community Noise Criteria

There are a number of different noise criteria measurements, some of which are described below:

CNEL = Community Noise Equivalent Level
This is used to characterize average sound levels over a 24-hour period, with weighting factors included for evening and nighttime sound levels. Leq values for the evening period (7:00 p.m. to 10:00 p.m.) are increased by 5 dB, while Leq values for the nighttime period (10:00 p.m. to 7:00 a.m.) are increased by 10 dB.
For a given set of sound measurements, the CNEL value will usually be about 1 dB higher than the Ldn value. In practice, CNEL and Ldn are often used interchangeably.

LAeqT = Equivalent continuous sound level
The steady state dB(A) level which would produce the same A-weighted sound energy over a stated period of time as a specified time varying sound.

Ldn = 24 hour LAeqT
LAeqT except 10dB is added to all levels measured between 2200 and 0700 hours.

LN = dB(A) level exceeded N% of the time
L90 is the dB(A) level exceeded 90% of the time and is commonly used to estimate ambient noise level.

LEPN = Effective Perceived Noise Level
A complex rating used to certify aircraft types for flyover noise. This includes corrections for pure tones and for the duration of the noise.

LNP = Noise Polution Level
A variation of LAeqT which accounts for short term variability in noise level. For a gaussian distribution of dB(A) level it is defined as:
LNP = Leq + (L10 - L90)

LPK = Peak Sound Pressure Level
ten times the common logarithm of the square of the ratio of the largest absolute value of the instantaneous sound pressure in a stated frequency band during a specified time interval to the reference sound pressure of 20 micro pascals.
NEF = Noise Exposure Forecast
A complex criterion for predicting future noise impact of airports. The computation considers Effective Perceived Noise Level of each type of aircraft, flight profile, number of flights, time of day, etc. Generally used in plots of equal NEF contours for zoning control around airports.

SEL = Sound Exposure Level
Used to describe the amount of noise from an event such as an individual aircraft flyover.

SENEL = Single Event Noise Exposure Level
The noise exposure level of a single event measured over the time between the initial and final points when the noise level exceeds a predetermined threshold.

Time Weighted Average (TWA)
The yardstick used by the Occupational Safety and Health Administration (OSHA) to measure noise levels in the workplace. It is equal to a constant sound level lasting eight hours that would cause the same hearing damage as the variable noises that a worker is actually exposed to (hearing loss, of course, occurs over long-term exposures).

Subjects: Audio