---
title: "Outdoor sound"
description: "Sound on its way through open air and the character of what arrives: the ISO 9613 outdoor-propagation model with its per-term attenuation breakdown, the wave-acoustic spherical ground effect and advanced barrier diffraction, and the NT ACOU 112 prominence and adjustment for impulsive sounds."
---

Outdoor sound assessment has two halves: predicting the level a source
delivers to a distant receiver, and judging the character of the sound that
actually arrives. The two pages of this section take one half each.

[Outdoor Sound Propagation](/phonometry/guides/outdoor-propagation/) is the
prediction half. Starting from a source's **sound power**, the ISO 9613-2
general method subtracts, octave band by octave band, every mechanism that
attenuates sound on its way: geometrical divergence, atmospheric absorption
(supplied by the pure-tone coefficient of **ISO 9613-1**), the ground effect
and barrier screening, with a meteorological correction for long-term
averages. The page keeps the per-term breakdown visible, so a prediction is
never a black box: you can see exactly which mechanism buys how many decibels
at which frequency.

[Spherical ground effect and advanced barriers](/phonometry/guides/ground-barriers/)
goes underneath the ISO 9613-2 fits to the wave acoustics they approximate: the
Weyl-Van der Pol spherical-wave reflection coefficient of a finite-impedance
ground, and barrier diffraction by the Kurze-Anderson Fresnel number, the exact
rigid half-plane, thick barriers and the coherent four-path barrier on the
ground, all resolving the frequency-dependent interference the octave-band terms
smooth away.

[Impulsive-sound prominence (NT ACOU 112)](/phonometry/guides/impulse-prominence/)
is the assessment half. Noise containing distinct impulses (hammering,
riveting, pile driving) annoys more than a steady sound of the same LAeq, and
the Nordtest method quantifies that: from the onset rate and level difference
of each impulse it computes a predicted **prominence**, and converts it into
the graduated adjustment KI that is added to the measured LAeq in a rating
level.

The surrounding machinery lives nearby: the rating levels and Lden that
assessments end in are covered in
[Integrated and Statistical Levels](/phonometry/guides/levels/), the tonal
counterpart of the impulsive adjustment in
[Objective audibility of tones in noise](/phonometry/guides/tone-audibility/),
and the sources that feed a propagation calculation in
[Sound Power](/phonometry/guides/sound-power/) and the
[Aircraft and wind energy](/phonometry/guides/sections/aircraft-wind/)
section.

## Pages in this section

- [Outdoor Sound Propagation](/phonometry/guides/outdoor-propagation/):
  ISO 9613-1 atmospheric absorption and the ISO 9613-2 general method with a
  per-term octave-band attenuation breakdown.
- [Spherical ground effect and advanced barriers](/phonometry/guides/ground-barriers/):
  the Weyl-Van der Pol spherical-wave ground reflection and wave-theoretic
  barrier diffraction (Kurze-Anderson, exact rigid half-plane, thick barriers
  and the coherent four-path barrier on the ground).
- [Impulsive-sound prominence (NT ACOU 112)](/phonometry/guides/impulse-prominence/):
  the predicted prominence of impulsive sounds and the graduated LAeq
  adjustment KI.
