OPEN LAB · ACOUSTICS
Acoustic map.
Demonstrative tool to visualise sound-level surveys and simulate propagation from point sources with the ISO 9613-2 method, including diffraction on real buildings (geometry from OpenStreetMap).
Acoustic map tool
Building detail
1 · Load measurements
2 · Visualisation
3 · Regulatory limit
Statistics
What the results represent
The statistics describe the loaded sound-level survey (CSV with lat, lon, Leq), not the propagation. POINTS is the number of survey receivers. MEAN LEQ is the arithmetic mean of the measured levels. MIN · MAX are the individual extremes. ABOVE LIMIT is the percentage of points exceeding the selected regulatory limit. The computed propagation (Predict mode, with optional building diffraction) is reported in the map status bar.
Export
How it works
How does Predict mode with diffraction work?
When you place a source, the tool downloads the geometry of nearby buildings (radius equal to the grid extent) from OpenStreetMap via the Overpass API. For each receiver it traces the source→receiver segment, finds the first intercepted building and computes the diffraction attenuation with the Maekawa formula — not the ISO 9613-2 §7.4 screening method — per octave band. Building height comes from the OSM height tag or building:levels × 3m.
When you place a source, the tool automatically downloads the geometry of nearby buildings (radius = grid extent) from OpenStreetMap via the Overpass API. For each grid receiver it traces the source→receiver segment and looks for the first intercepted building. If one exists, it computes the diffraction attenuation with the Maekawa formula, ISO 9613-2 §7.4, per 1/3-octave band:
delta = (d_ST + d_TR) - d_SR // path difference N = 2·delta/lambda // Fresnel number A_dif = 10·log10(3 + 20·N) // attenuation dB (clamp 0-25)
Where T is the top elevation of the intercepted building. The elevation is taken from the OSM height tag if present, otherwise computed as building:levels × 3m, falling back to the default value set in the interface.
Which attenuation terms does it compute?
The tool sums four attenuation terms: A_div = 20·log₁₀(d) + 11, the spherical geometric divergence (ISO 9613-2 §7.1); A_atm = α(f, T, RH)·d, the atmospheric absorption (ISO 9613-1); A_gr, the ground effect with G-factor (ISO 9613-2 §7.3.2); and A_dif, the Maekawa diffraction (ISO 9613-2 §7.4).
A_div = 20·log₁₀(d) + 11— spherical geometric divergence of the single point (ISO 9613-2 §7.1)A_atm = α(f, T, RH) · d— atmospheric absorption (ISO 9613-1)A_gr— ground effect, general formula with G-factor (ISO 9613-2 §7.3.2)A_dif— Maekawa diffraction (ISO 9613-2 §7.4) ★ new in v0.2
What does this tool not do?
This prototype does not compute: multi-diffraction (several buildings in cascade); lateral diffraction (around the building, not only over the top); multiple, line or area sources; multiple reflections on façades; the CNOSSOS-EU or NMPB-Routes-2008 models; and it does not check building-height accuracy, estimated from building:levels when the height tag is missing.
- Multi-diffraction (several buildings in cascade)
- Lateral diffraction (around the building, not only over the top)
- Multiple, line or area sources
- Multiple reflections on façades
- CNOSSOS-EU or NMPB-Routes-2008 model
- Building-height accuracy check (estimated from building:levels when
heightis missing)
Validation
Source Lw=100 dB(A) flat broadband, hs=1.5m, hr=1.5m, soft ground, T=15°C, RH=70%.
| Distance | Computed | Expected | Δ |
|---|---|---|---|
| 10 m | — | 65–72 | — |
| 100 m | — | 40–48 | — |
| 500 m | — | 20–28 | — |
Normative references
- ISO 9613-1:1993 — Acoustics — Attenuation of sound during propagation outdoors. Part 1: Calculation of the absorption of sound by the atmosphere.
- ISO 9613-2:2024 — Acoustics — Attenuation of sound during propagation outdoors. Part 2: Engineering method for the prediction of sound pressure levels outdoors. Current edition, implemented in the tool. Implements updated Dz and Kmet formulas (§7.4.1) compared to the 1996 edition.
- ISO 9613-2:1996 — Earlier edition. Reported in this documentation as didactic reference, to allow verification of continuity with results from software based on earlier editions of the standard.
- Maekawa, Z. (1968). Noise reduction by screens. Applied Acoustics, 1(3), 157-173. DOI 10.1016/0003-682X(68)90020-0.
- Italian Law 447/1995 — Framework law on noise pollution (Italian regulatory framework).
- Italian DPCM 14/11/1997 — Noise source limit values: immission, emission, quality limits by acoustic zone class (Tables A, B, C, D).
- Italian DM 16/03/1998 — Technical methods for measuring noise pollution (reference for sound level surveys imported into the tool).
- Italian Legislative Decree 194/2005 — Implementation of EU Directive 2002/49/EC on strategic noise mapping.
Note on the ISO 9613-2 standard. The calculation engine implements the second edition ISO 9613-2:2024, which redefines the diffraction loss Dz and the meteorological correction Kmet compared to the first 1996 edition. The 2024 edition corrects known "shortcomings" with low barriers and large source-to-receiver distances. The 1996 formulation is reported in this documentation as didactic reference, useful for verifying continuity with results from software still based on the previous edition — transition still ongoing internationally. Figures from the two formulations diverge appreciably for low barriers and long-range propagation, and negligibly for short-range urban scenarios.