Day–Night Equivalent SPL

In the United States during the 1970s, the Environmental Protection Agency (EPA) developed a measure, from the equivalent SPL, known as the day–night equivalent level (DNL) or L_dn that accounts for the different response of people to noise during the night [31] given by

(6.7)

where L_d is the 15‐hour daytime A‐weighted equivalent SPL (from 07:00 to 22:00 hours) and L_n is the 9‐hour nighttime equivalent SPL (from 22:00 to 07:00 hours). The nighttime noise level is subjected to a 10‐dB penalty because noise at night is deemed to be much more disturbing than noise during the day. This 10‐dB nighttime penalty is analogous to the 10‐dB nighttime penalty applied in both the composite noise rating (CNR) and the noise exposure forecast (NEF), as described in Section 6.12. The DNL has become increasingly used in the United States and some other countries to evaluate community noise and in particular airport noise [29, 32]. In 1980 the U.S. Federal Interagency Committee on Urban Noise (FICON) adopted L_dn as the appropriate descriptor of environmental noise in residential situations [29–33].

EXAMPLE 6.8

The energy‐equivalent hourly A‐weighted SPLs in a residential community are measured using an integrating sound level meter, and the results are presented in Table 6.3. Calculate the daytime and nighttime A‐weighted equivalent SPL, and the day‐night equivalent level in the community.

SOLUTION

The daytime average A‐weighted level is calculated considering measurements 1–15 giving

The nighttime average level is calculated considering measurements 16–24 resulting

Consequently, the day‐night equivalent A‐weighted level is

EXAMPLE 6.9

Assume for the noise profile presented in Table 6.3 that a factory nearby produced an intense venting noise for a period of 10 seconds, at an A‐weighted SPL of 95 dB during the 22:00 hours night period. What would be the effect on the day‐night equivalent level?

SOLUTION

First we must determine the effective A‐weighted hourly level for the 22:00 time period. This level must combine the normal A‐weighted background noise of 60 dB that is on 3590 seconds out of the hour (3600 seconds) and 95 dB that is on for the remaining 10 seconds. Therefore, the new A‐weighted value for the row 16 in Table 6.3 is

The daytime equivalent SPL L_d is not affected by this venting noise and we have to replace 60 dB by the level including the contribution of the venting noise (69.9 dB) in Table 6.3 and repeat the calculation for L_n. This gives a nighttime A‐weighted equivalent level of 62.2 dB. Finally, the day‐night A‐weighted equivalent level is calculated as in Example 6.8, resulting in 68.8 dB, an increase of almost 3 dB that represents a potential significant source of annoyance to the residents of the community.

Table 6.3 Data used in Example 6.8.

Number	Time	A‐weighted sound pressure level, dB
1	07:00	60
2	08:00	65
3	09:00	65
4	10:00	62
5	11:00	63
6	12:00	63
7	13:00	60
8	14:00	60
9	15:00	65
10	16:00	65
11	17:00	65
12	18:00	64
13	19:00	64
14	20:00	62
15	21:00	60
16	22:00	60
17	23:00	60
18	00:00	58
19	01:00	57
20	02:00	57
21	03:00	57
22	04:00	57
23	05:00	57
24	06:00	60