Audio Engineering

Measurement 51

2.12 The Equivalent Level (LEQ) in Noise Measurements ..............................................

Increasingly, acoustical workers in the noise control fi eld are erecting an interesting
edifi ce of measurement systems. A number of these measurement systems are based
on the concept of average energy. Suppose, for example, that we have some means of
collecting all of the A-weighted sound energy that arrives at a particular location over a

Table 2.8 : Recommended Descriptor List

Term A weighting Alternative a

A weighting

Other weighting b Unweighted

Sound (pressure) level c LA LpA LB , LpB LP

Sound power level LWA LWB LW

Maximum sound level Lmax LAmax LBmax Lpmax

Peak sound (pressure) level LApk LBpk Lpk

Level exceeded x % of the time Lx LAx LBx LPx

Equivalent sound level Leq LAeq LBeq Lpeq

Equivalent sound level over

time ( T ) d

Leq(T) LAeq(T) LBeq(T) Lpeq(T)

Day sound level Ld LAd LBd Lpd

Night sound level Ln LAn LBn Lpn

Day–night sound level Ldn LAdn LBdn Lpdn

Yearly day–night sound level Ldn(Y) LAdn(Y) LBdn(Y) Lpdn(Y)

Sound exposure level LS LSA LSB LSp

Energy average value over

(nontime domain) set of

observations

Leq(e) LAeq(e) LBeq(e) Lpeq(e)

Level exceeded x % of the total

set of (nontime domain)

observations

Lx(e) LAx(e) LBx(e) Lpx(e)

Average Lx value Lx LAx LBx Lpx

a “ Alternative ” symbols may be used to assure clarity or consistency.

b Only B weighting is shown. Applies also to C, D, and E weighting.

c The term “ pressure ” is used only for the unweighted level.

d Unless otherwise specifi ed, time is in hours [e.g., the hourly equivalent level is Leq( 1 ) ]. Time may be specifi ed in

nonquantitative terms [e.g., could be specifi ed as Leq(WASH) to mean the washing cycle noise for a washing machine].