Equivalent Energy Level

The average intensity over a given period of time, given the symbol L_eq and expressed in decibels relative to the reference intensity of the threshold of hearing.

The number of hours over which the average is taken is often put in brackets, e.g. L_eq (24) denoting the 24-hour energy average. When nighttime levels (from 2200 to 0700) are given a 10 dB boost in calculating the 24-hour average (to compensate for sleep disturbance), the level is called the day-night equivalent Noise Level and is given the symbol L_dn. By counting loudness and duration, L_eq is often called the exposure level.

Note that L_eq is not identical with the average dB level (L₅₀), although it will be similar when the fluctuation in dB is small (i.e. less than 5 dB). For greater fluctuations, Leq is higher, since the measurement method gives greater weight to higher intensities. For instance, the decibel average of three measurements of 20, 50 and 80 dBA is 50 dBA, but L_eq = 75 dBA. As a result, the measurement is generally regarded as the best indicator of the effects of duration and loudness.

An L_eq(24) of 70 has come to be regarded as the noise exposure threshold of hearing damage (see damage-risk criteria). L_dn = 55 similarly is regarded as the threshold of expressed community annoyance because it has been found to be the level for which 17% of the population will express a high degree of annoyance. Correlation of exposure levels with annoyance is extremely difficult as it depends on such factors as the relation between the person and the noise maker, individual listening habits, education and life style, attitudes towards the necessity or preventability of the noise (including opinions as to the intentions of the noise maker), previous noise exposure, and the means available for complaint.

Compare: Community Noise Equivalent Level, Noise and Number Index, Noise Level, Noise Pollution Level, Sound Level, Sound Level Meter, Sound Power Level, Sound Pressure Level, Traffic Noise Index.