6.7 THE DAY^NIGHT LEVEL

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6.7.1 EPA Criteria

The U.S. Environmental Protection Agency (EPA) has investigated the

effect of noise on people and the effect of the noise from the environment

on the health and welfare of the affected people (EPA, 1974). The EPA

concluded that the A-weighted sound level correlated as well with human

response to noise as more complex measures. As a result, the A-weighted

sound level was selected as the basis for environmental noise criteria.

Generally, the A-weighted sound level does not remain constant during

any extended period at a particular location. It would be incorrect to

average directly the decibel readings during the period. Instead, one should

use the energy-equivalent sound level, Leq, which is the sound level averaged

on an energy basis:

Leq ј 10 log10Ѕ_tj10Lj=10_ (6-7)

Acoustic Criteria 247

TABLE 6-12 Average Community Reaction to Noise Based on the

Composite Noise Rating LCNR

Corrected composite noise

rating, LCNR, dB Community response

Percent of population

complaining

39 dB or less No reaction

40–45 dB Mild annoyance 1

46–50 dB Sporadic complaints 2

51–55 dB Widespread complaints 7

56–69 dB Threats of legal action 12

70 dB or greater Vigorous legal action 22

TABLE 6-13 Solution for Example 6-4

Octave band center frequency, Hz

63 125 250 500 1,000 2,000 4,000 8,000

Lp(OB), dB 43 50 55 61 66 69 71 69

No, dB — 33 46 58 66 71 75a 74

LCNR-65 86 78 72 68 65 63 60 59

Reduction, dB — — — — 1 6 11 10

aLargest value.

Copyright © 2003 Marcel Dekker, Inc.

The quantity tj is the fraction of the time period that the noise has an

A-weighted sound level of Lj, and Lj is the A-weighted sound level during the

jth time interval.Many sound level meters have the feature that this quantity

may be measured directly with the meter.

The EPA found (not surprisingly) that people were more sensitive to

noise during the nighttime hours than during the daytime period. From our

discussion of the environmental noise rating parameter in Sec. 6.6, we found

that noise that occurred only during the daytime was about 10dB less

annoying than noise that occurred during the nighttime. The correction

factor from Table 6-11 for noise during the daytime only is CF ј _10dB,

whereas CF ј 0 dB for noise during the nighttime.

Based on this observation, the EPA suggested a modification of the

equivalent sound level, called the day–night average sound level, LDN, to take

into consideration the additional annoyance of noise at nighttime. The day–

night level was developed originally to be used as an aid in land-use

planning. For this parameter, the nighttime equivalent sound levels were

increased by 10 dB for the time period from 10:00 p.m. to 7:00 a.m. This

nighttime period involves 9 hours, or a fraction of 0.375 of the 24-hour day,

and the daytime period involves 15 hours, or a fraction of 0.625 of the

24-hour day. The day–night level is, accordingly, defined by the following

expression:

LDN ј 10 log10Ѕр0:625Ю 10LD=10 юр0:375Ю 10рLNю10Ю=10_ (6-8)

The quantity LD is the equivalent sound level during the daytime hours, and

LN is the equivalent sound level during the nighttime.

According to the EPA studies, the effects given in Table 6-14 would be

observed if the day–night level of 55 dBA is present. For outdoor activities

that should be free of speech interference and produce no significant annoyance,

the EPA recommends the criterion that LDN _ 55 dBA. Similarly, for

indoor activities, the EPA recommendation is that LDN _ 45 dBA. For

minimum hearing loss (no more than 5 dB noise-induced permanent threshold

shift for 96% of the population) over a period of 40 years, the EPA

recommends that the noise exposure during the 24-hour day be limited by

LDN _ 70 dBA.

Example 6-5. During a 1-hour period, the A-weighted sound level is

70 dBA for 30 minutes, 75 dBA for 20 minutes, and 80 dBA for 10 minutes.

Determine the energy equivalent sound level.

The fractions for each interval are р30=60Ю ј 0:5000 for 70 dBA,

0.3333 for 75 dBA, and 0.1667 for 80 dBA. Using Eq. (6-7), we find the

energy-equivalent sound level:

248 Chapter 6

Copyright © 2003 Marcel Dekker, Inc.

Leq ј 10 log10Ѕр0:5000Ю 107:0 юр0:3333Ю 107:5 юр0:1667Ю 108:0_

Leq ј 10 log10р3:2208_107Ю ј 75:1dBA

Example 6-6. The hourly equivalent sound levels measured outdoors at a

particular location are given in Table 6-15. Determine the day–night level

for this data.

During the daytime, the fraction of time for each sound level is calculated

as follows:

50dBA: 3 hours, or tј 3=15 ј 0:2000

60dBA: 10 hours, or t ј 10=15 ј 0:6667

70dBA: 2 hours, or tј 2=15 ј 0:1333

The equivalent sound level during the daytime is found from Eq. (6-7):

LD ј 10log10Ѕр0:2000Ю 105:0 юр0:6667Ю 106:0 юр0:13333Ю 107:0_

LD ј 63:1 dBA

For the 9 hours during the nighttime, the fraction of time for each

sound level is calculated as follows:

30dBA: 5 hours, or t ј 5=9 ј 0:5556

40dBA: 4 hours, or t ј 4=9 ј 0:4444

Acoustic Criteria 249

TABLE 6-14 Effects Corresponding to a Day–Night Level of 55 dBA

Condition Magnitude of the effect

Speech indoors 100% sentence intelligibility with a 5 dB margin of safety

Speech outdoors 99% sentence intelligibility at 1m (3.3 ft) spacing; 95%

sentence intelligibility at 3.5m (11.5 ft) spacing

Average community

reaction

No evident reaction; 7 dB below the beginning of threats

of legal action

Complaints About 1% may complain, depending on the person’s

attitude and other non-noise-related factors

Annoyance About 17% may be somewhat annoyed

Attitude toward area Noise is essentially one of the least important factors

influencing the person’s attitude toward the area

Source: EPA (1974).

Copyright © 2003 Marcel Dekker, Inc.

The equivalent sound level during the nighttime is found from Eq. (6-7) also:

LN ј 10 log10Ѕр0:5556Ю 103:0 ю р0:4444Ю 104:0_ ј 37:0 dBA

The day–night level is found from Eq. (6-8):

LDN ј 10 log10Ѕр0:625Ю 106:31 ю р0:375Ю 10р37:0ю10Ю=10_ ј 61:1 dBAрDNЮ

We note that this value is greater than the EPA recommended value of

55 dBA for outdoor activity. To reduce the day–night level to 55 dBA, one

could install barriers, for example, to reduce the noise during the daytime

hours only. The required reduction value of the daytime sound level could

be calculated as follows:

105:50 ј р0:625Ю 10LD=10 ю р0:375Ю 104:70

LD ј 56:8 dBA

If the sound level during the daytime could be reduced by

р63:1 _ 56:8Ю ј 6:3 dBA, the day–night level would be reduced to 55 dBA.

6.7.2 Estimation of Community Reaction

If noise spectrum data are not available, the day–night level of the background

noise, with suitable correctors, may be used to estimate the anticipated

community response to the environmental noise:

LDNрcorrectedЮ ј LDNрmeasuredЮ ю CFDN (6-9)

250 Chapter 6

TABLE 6-15 Data for Example 6-6

Daytime Nighttime

Timea LA, dBA Timea LA, dBA Timea LA, dBA

7:00 a.m. 50 3:00 p.m. 60 10:00 p.m. 40

8:00 a.m. 60 4:00 p.m. 60 11:00 p.m. 40

9:00 a.m. 70 5:00 p.m. 70 12:00 mid 40

10:00 a.m. 60 6:00 p.m. 60 1:00 a.m. 30

11:00 a.m. 60 7:00 p.m. 60 2:00 a.m. 30

12:00 noon 60 8:00 p.m. 50 3:00 a.m. 30

1:00 p.m. 60 9:00 p.m. 50 4:00 a.m. 30

2:00 p.m. 60 5:00 a.m. 30

6:00 a.m. 40

a‘‘Time’’ refers to the hour beginning with the time given in the table.

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The day–night sound level contains explicitly the effect of annoyance due to

noise during the nighttime, so the other effects—such as location, time of the

year, etc.—are accounted for with the correctors given in Table 6-16.

The anticipated community response to environmental noise in terms

of the day–night level of the noise is given in Table 6-17. This data may be

used in a manner similar to that for the environmental noise rating to design

for satisfactory community response to planned introduction of a noise

source outdoors.

Example 6-7. The noise levels in a normal suburban area are given in

Table 6-18. The area has had some prior experience with intrusive noises.

There are no pure tone components of the noise, and it is not impulsive. The

Acoustic Criteria 251

TABLE 6-16 Correctors to be Added to the Measured Day–Night Level for

Various Influencing Factorsa

Influencing factor Description of condition CFDN, dBA

Noise spectrum Pure tones or impulsive noise present ю5

No pure tone or impulsive sounds 0

Type of location Quiet suburban or rural community ю10

Normal suburban community ю5

Urban residential community 0

Noisy urban residential community _5

Very noisy urban community _10

Time of year Summer or year-round 0

Winter only or windows always closed _5

Previous noise exposure No prior experience with the intruding

noise

ю5

Some prior experience with the noise or

where the community is aware that

good-faith efforts are being made to

control noise

0

Considerable experience with the noise

and the group associated with the

source of noise has good community

relations

_5

Aware that the noise source is necessary,

of limited duration, and/or an

emergency situation

_10

aOnly one correction factor should be used from each category.

Copyright © 2003 Marcel Dekker, Inc.

noise source will be present year-round. Determine the anticipated community

response to the noise source.

The equivalent sound level for the daytime hours is found from Eq.

(6-7):

LD ј 10 log10Ѕр0:2667Ю 106:0 ю р0:4000Ю 105:5 ю р0:3333Ю 105:0_

LD ј 56:3 dBA

The equivalent sound level during the nighttime is found from Eq. (6-7) also:

LN ј 10 log10Ѕр0:2222Ю 104:5 ю р0:7778Ю 104:0_ ј 41:7 dBA

The day–night level is found from Eq. (6-8):

LDN ј 10 log10Ѕр0:625Ю 105:63 ю р0:375Ю 10р41:7ю10Ю=10_ ј 55:1 dBAрDNЮ

252 Chapter 6

TABLE 6-17 Average Community Reaction to Noise

Based on the Day–Night Level, LDN

Corrected day–night level,

LDN(corrected) Expected community response

<62 dBA(DN) No reaction

62–67 dBA(DN) Complaints

67–72 dBA(DN) Threats of community action

>72 dBA(DN) Vigorous community action

TABLE 6-18 Data for Example 6-7

Duration A-weighted level Fraction

Daytime:

4 hours 60dBA t ј 4=15 ј 0:2667

6 hours 55dBA t ј 6=15 ј 0:4000

5 hours 50dBA t ј 5=15 ј 0:3333

Nighttime:

2 hours 45dBA t ј 2=9 ј 0:2222

7 hours 40dBA t ј 1=9 ј 0:7778

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The correction factors for other influences are found in Table 6-16 as

follows:

Noise spectrum .......................................... _0

Type of location ........................................ ю5

Time of year (year-round) ......................... _0

Previous noise exposure ............................. _0

______________

Total .......................................................... CFDN ј ю5dBA

The corrected day–night level is as follows:

LDNрcorrectedЮ ј 55:1ю5 ј 60:1dBAрDNЮ

The anticipated community reaction from Table 6-17 is no reaction.

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