ISO 9613-1:1993

Overview

ISO 9613-1:1993 - "Acoustics - Attenuation of sound during propagation outdoors - Part 1: Calculation of the absorption of sound by the atmosphere" specifies an analytical method for computing atmospheric absorption of sound during outdoor propagation. It provides attenuation coefficients and formulae primarily for pure-tone sounds, covering frequencies from 50 Hz to 10 kHz, ambient temperature -20 °C to +50 °C, relative humidity 10–100%, and a reference pressure of 101,325 kPa (one atmosphere). The standard also supplies extensions for ultrasonic frequencies, lower pressures and guidance for converting humidity measures for practical calculations.

Key topics and technical requirements

• Attenuation coefficient definition: Atmospheric absorption expressed as an attenuation coefficient (dB/m or dB/km) that depends on frequency, temperature, humidity (molar water vapor concentration) and pressure.
• Calculation formulas: Analytical expressions (with tabulated reference values) to compute pure‑tone attenuation coefficients; users are advised to use the equations rather than interpolating table entries.
• Wideband methods: Procedures for calculating attenuation of wideband sounds using fractional‑octave band filters (midband approach) and an alternate spectrum‑integration method (annex D).
• Assumptions & ranges: Standard assumes a uniform atmosphere for primary formulae; annex C discusses extensions to inhomogeneous atmospheres (varying meteorological conditions with height).
• Accuracy guidance: Estimated uncertainties are provided for different variable ranges (e.g., ±10% under common environmental ranges, larger outside those bounds).
• Informative annexes: Annexes A–F describe underlying physical mechanisms, humidity conversions, and computational details.

Practical applications and users

ISO 9613-1 is essential for anyone predicting environmental noise or modeling outdoor sound propagation where atmospheric absorption is significant. Typical users:

• Environmental acousticians and noise consultants performing long‑range noise predictions (road, rail, industrial sources).
• Acoustic engineers developing sound propagation models and tools or validating simulation software.
• Urban planners and regulators assessing noise impact and compliance with limits.
• Researchers studying atmospheric effects on sound, including ultrasonic and high‑altitude propagation.
• Software developers implementing standardized attenuation algorithms in noise mapping and acoustic modeling products.

Practical uses include converting measured sound pressure levels to account for different meteorological conditions, computing frequency‑dependent loss over propagation paths, and integrating atmospheric absorption into comprehensive outdoor propagation models.

Related standards

• ISO 9613-2 - General method of calculation (ground effects, refraction)
• ISO 2533 - Standard Atmosphere (reference pressure/temperature)
• ISO 266 and IEC 225 - Preferred frequencies and fractional‑octave filter standards

Keywords: ISO 9613-1, atmospheric absorption, attenuation of sound, outdoor sound propagation, acoustic attenuation coefficients, environmental noise prediction.