Outdoor Propagation Sound

Overview

Engineering reference data for Outdoor Propagation Sound in acoustics.

Key Formulas

Speed of Sound

$c = \sqrt{\gamma R T}$

Speed of sound in an ideal gas.

Sound Level

$L = 10 \log_{10}(I/I_0)$

Decibel level.

Wavelength

$\lambda = c / f$

Wavelength = speed / frequency.

Variables

Symbol	Description	Unit
$c$	Speed of sound	m/s
$L$	Sound level	dB
$\lambda$	Wavelength	m
$f$	Frequency	Hz

Propagation Characteristics

Spherical Propagation (Q = 1) When sound radiates uniformly in all directions from a point source in free field ($R \approx \infty$): $L_p = L_N - 20 \log_{10}(r) - 11$

Hemi-Spherical Propagation (Q = 2) When the source is located near a single large reflecting surface (e.g., ground): $L_p = L_N - 20 \log_{10}(r) - 8$

Distance Attenuation Rules:

• Point Source: Sound level decreases by 6 dB when the distance doubles ($20 \log_{10}(2) \approx 6$).
• Linear Source: Sound level decreases by 3 dB when the distance doubles ($10 \log_{10}(2) \approx 3$).

Directivity Coefficients

The directivity coefficient ($Q$) describes the radiation pattern of the sound source.

References

• Original Source