Environment and transport
Environmental noise is a source-path-receiver problem stretched over hundreds of metres of open air. This section covers both ends of it. The outdoor sound pages handle the path and the assessment: ISO 9613 predicts, band by band, how much level survives divergence, air absorption, the ground and any barrier on the way to a receiver, and NT ACOU 112 quantifies when impulsive character makes the received sound more annoying than its LAeq suggests.
The aircraft and wind energy pages handle transport sources that come with their own internationally fixed metrics. Aircraft noise certification runs on the Effective Perceived Noise Level of ICAO Annex 16, with the airport-contour machinery of ECAC Doc 29 built on top; helicopters get the directional noise-hemisphere source model of ECAC Doc 32; and wind turbines are rated by the apparent sound power and tonal audibility of IEC 61400-11. What unites them is the pattern: a carefully standardised source descriptor plus standardised propagation adjustments.
This section leans on the core toolkit more than any other: the rating levels and Lden that environmental assessment ends in live in Integrated and Statistical Levels, and the atmospheric absorption that every propagation model consumes is shared with the room and materials pages. Start with Outdoor Sound Propagation; it introduces the source-path-receiver bookkeeping the transport pages reuse.
The path from an outdoor source to a receiver, and the character of what arrives.
- Outdoor Sound Propagation: atmospheric absorption (ISO 9613-1) and the ISO 9613-2 general method with its per-term attenuation breakdown.
- Impulsive-sound prominence (NT ACOU 112): the predicted prominence of impulsive sounds and the graduated adjustment added to LAeq.
Transport and energy sources with their own certification metrics.
- Aircraft noise: Effective Perceived Noise Level: the ICAO Annex 16 EPNL, the IEC 61265 measurement-system verifier, SAE ARP 5534 atmospheric absorption and ECAC Doc 29 NPD interpolation.
- Rotorcraft noise: the hemisphere method: the ECAC Doc 32 noise-hemisphere source model with its propagation adjustments.
- Wind-turbine noise: sound power and tonal audibility: the IEC 61400-11 apparent sound power level and tonal-audibility chain.