proposed integrated complex for delhi judicial academy

Rapid Environmental Impact Assessment (REIA) Study for Proposed Integrated Complex for Delhi Judicial Academy,
National Law School, and National Institute for Mediation & Conciliation at Dwarka, New Delhi
the A weighted Scale which is measured as dB (A). This is more suitable for audible range of
20 to 20,000 Hz.
The acoustical environment varies dynamically in magnitude and character through out most
communities. The noise level variation can be temporal, spectral and spatial. The residential noise
level is that level below which the ambient noise does not seem to dropdown during the given
interval of time and is generally characterised by unidentified sources. Ambient noise level is
characterised by significant variations above a base or a residential noise level. The maximum
impact of noise is felt on urban areas, which is mostly due to the commercial activities and
vehicular movement during peak hours of the day.
Measured noise levels displayed as a function of time provides a useful scheme for describing the
acoustical climate of a community. Noise levels recorded at each station with a time interval of
about 30 minutes are computed for equivalent noise levels (L eq ). Equivalent noise level is a single
number descriptor for describing time varying noise levels.
L eq is the equivalent continuous sound level that is equivalent to the same sound energy as the
actual fluctuating sound measured in the same period. This is necessary because sound from noise
source often fluctuates widely during a given period of time. This is calculated from the following:
L day is defined as the equivalent noise level measured over a period of time during day (6 am to 10
pm).
L night is defined as the equivalent noise level measured over a period of time during night (10 pm to
6 am).
A noise rating developed by Environment Protection Agency, USEPA for specification of
community noise from all the sources is the Day-Night Sound Level, L dn .
The noise rating developed for community noise from all sources is the Day- Night Sound Level
(L dn ). It is similar to a 24 hr equivalent sound level except that during night time period (10 pm to 6
am) a 10 dB (A) weighting penalty added to the instantaneous sound level before computing the 24
hr average.
L eq = 10 log 1/T N i=1 Ti (10) Li/10
Where, T = total time of sampling,
Ti = Time duration of ith phase
N = Number of phases
Li = L eq for the ith phase
This night time penalty is added to account for the fact that noise during night when people usually
sleep is judged as more annoying than the same noise during the day time.
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