Noise Impact Assessment Calculator

This calculator predicts the A-weighted sound level a receiver will experience from a point noise source, following the outdoor sound propagation framework in ISO 9613-2:1996 (Acoustics — Attenuation of sound during propagation outdoors — Part 2: General method of calculation), the international standard method for predicting environmental noise from a source at a receiver location. It starts with geometric divergence — the dominant effect for most distances — using the inverse-square-law formula 20×log10(distance/reference distance), which alone accounts for a 6 dB drop every time distance doubles. On top of that it layers atmospheric absorption (a small, fixed 0.005 dB per meter, representative of a 500 Hz tone at moderate temperature and humidity) and a ground effect term that only kicks in past 100 meters, subtracting more attenuation over soft ground (grass, soil) than hard ground (pavement, water).

If a barrier height is entered, the calculator applies the Maekawa approximation: it computes the extra path length sound must travel to diffract over the barrier, converts that into a Fresnel number, and derives an insertion loss capped at a realistic 20 dB maximum. The received level is then compared against a regulatory threshold that depends on receiver land use — 50 dBA for residential nighttime up to 72 dBA for industrial — and the calculator reports the exceedance plus, if you're over the limit with no barrier yet, reverse-solves the Maekawa formula for the barrier height that would bring you into compliance. Because this uses a single representative frequency (500 Hz) rather than full octave-band analysis, and simplifies barrier geometry to a straight midpoint obstruction, treat results as a planning-level screening tool — a full regulatory submission typically needs frequency-specific modeling software and site-specific terrain data.