声级

概述

昼夜声级 (Ldn) 是美国环保署的指标，汇总 24 小时期间内 A 加权等效声级。夜间时段（晚上 10 点到早上 7 点）会受到 +10 dB 的惩罚，以考虑睡眠期间人类对噪音敏感度的增加。该指标广泛用于环境噪音评估、土地利用规划和法规合规。

关键公式

昼夜声级

$L_{dn} = 10 \log_{10}\left(\frac{1}{24}\left(15 \cdot 10^{L_d/10} + 9 \cdot 10^{(L_n + 10)/10}\right)\right)$

其中 15 小时为白天，9 小时为夜间。

变量

典型室外声级

计算器

单位换算器

The source page includes a Unit Converter heading. Sound levels are logarithmic, so this converter works with sound-pressure ratios, intensity ratios, and dB differences rather than treating dB as a linear unit.

计算示例

With daytime level $L_d = 70 \, \text{dBA}$ and nighttime level $L_n = 50 \, \text{dBA}$:

$L_{dn} = 10 \log_{10}\left(\frac{15 \times 10^{7} + 9 \times 10^{6}}{24}\right) = 68.2 \, \text{dBA}$

The 10 dB nighttime penalty effectively treats the 50 dBA nighttime environment as 60 dBA when weighted.

Sound Descriptors

The EPA uses four sound descriptors to evaluate noise impact on health and welfare:

• A-weighted sound level – instantaneous, frequency-weighted measurement
• Sound Exposure Level (Ls) – total sound energy in a single event, normalized to 1 second
• Equivalent Sound Level (Leq) – constant level with the same energy as the varying sound over a given period
• Day-Night Sound Level (Ldn) – 24-hour Leq with a 10 dB nighttime penalty

还原的原始源表

以下表格还原自原始来源页面，以保留完整的参考数据。

Typical Day and Night Sound Level vs. Location

工程要点

• A 10 dB increase in Ldn roughly doubles the perceived loudness; Ldn values above 55 dBA are generally considered incompatible with residential tranquility.
• The +10 dB nighttime penalty reflects the EPA's weighting of sleep disturbance, not a physical measurement change.
• Ldn is community-averaged and does not capture single-event extremes like aircraft flyovers; for those, Sound Exposure Level (Ls) or Maximum Sound Level (Lmax) may be more appropriate.
• Measurement positions, ground effects, and meteorological conditions can shift outdoor Ldn readings by several dB; standards such as ANSI S12.9 govern measurement procedures.

参考资料

• Original Source – Engineering ToolBox