Adding up four sound levels in dBA. Estimating the reverberation time of an untreated classroom. Checking whether a receiver falls inside the relevant strip of a road under the Italian DPR 142/04. These are first-approximation tasks that come up every week for anyone working in acoustics — and for which opening a full forensic-grade software package is overkill.
Six tools now cover these calculations, free and directly in the browser. They join the acoustic map and the barrier calculation already published, and where the calculation is the same they share the same engine. They are demonstrative tools — exploration, teaching, preliminary analysis — not substitutes for a report signed by a qualified acoustician.
What we have released
Sound level composition
Logarithmic sum of N levels — the typical case is several sources acting together on the same receiver. Simple input: a list of Leq values in dBA; output the composite Leq. Useful for the quick check of multi-source scenarios, for verifying aggregate measurements, and in university teaching, where the most common mistake is still adding decibels arithmetically. References: ISO 3744 (2025 edition in force; UNI 9884:1997 is withdrawn without replacement).
→ /en/tools/level-composition/
L. 447/95 differential criterion
Compliance check against the differential criterion (5 dB by day, 3 dB by night) defined by the Italian DPCM 14/11/1997 (decree setting noise-source limit values), Art. 4. Input: the ambient level and the residual level, with and without the source under examination, in open- or closed-window mode. Output: the ΔL and the verdict, with correct handling of the exemptions — Art. 4 §2 (levels below threshold) and §3 (exclusions: transport infrastructure, private behaviour, plant serving the same building). Automatic exclusion of acoustic Class VI.
→ /en/tools/italian-differential-criterion/
Maekawa explorer
An interactive explorer of single-edge diffraction. It compares, on the same geometry, the three methods offered by the barrier calculator — ISO 9613-2:2024, ISO 9613-2:1996 and Maekawa 1968 — as source-barrier-receiver geometry and frequency change, with instant output. It shows the Fresnel number N = 2δ/λ and plots the Maekawa Att(N) curve. A teaching tool for understanding why a barrier attenuates high frequencies more than low ones. It uses the same physics engine as the barrier calculator.
LEX,8h — occupational noise exposure
Calculation of the daily personal noise exposure level under the Italian D.Lgs 81/08 (Consolidated Workplace Safety Act), Title VIII Chapter II. Input: a list of exposures (duration + Leq); output the LEX,8h and the comparison with the lower exposure action value (80 dBA), the upper one (85 dBA) and the exposure limit value (87 dBA). Designed for the noise risk-assessment stage in workplaces.
Reverberation time
Calculation of T60 with three historical formulations — Sabine (1898), Eyring (1930), Millington (1932) — per octave band. A materials library with absorption coefficients α cited from authoritative sources (Cremer-Müller, Vorländer, Beranek). It is a pure calculator: the user gets the numbers, while the regulatory judgement — UNI 11532-2:2020, Italian CAM Edilizia (green public-procurement criteria) and the like — remains the designer’s responsibility.
→ /en/tools/reverberation-time/
DPR 142/04 road-noise check
Compliance check of the sound level at a receiver against the limits of the Italian DPR 142/04 (decree on road-traffic noise): road classification (types A–F), status (new or existing), the relevant acoustic strip, the regime for sensitive receivers and the interaction with DPCM 14/11/1997 outside the strip. Two-way cross-link with acmap: the level computed at a receiver can be passed straight into the DPR check.
→ /en/tools/italian-road-noise-limits/
The perimeter, and what happens to the data
The calculation is entirely client-side and there is no backend: the files you load stay in the browser. The two tools that download buildings or map tiles do query external services (Overpass, tile servers), which receive the coordinates and the requested area — relevant information if you work on a confidential site.
The assumptions of each model — diffuse field, geometric simplifications, accepted hypotheses — are in the tool documentation. Where the calculation is the same, the tools share the same engine: the acoustic map, the barrier calculation and the Maekawa explorer compute diffraction with the same functions, so they return the same numbers on the same geometry. Where the code is a project of its own it is public on GitHub under the Apache 2.0 licence.
For forensic use — acoustic impact assessments, limit validation, expert reports — these tools are not enough: a calculation model adequate to the required methodology is needed, and a qualified technician responsible for it. “Certified software” is not a category the regulation provides for. DM 29/11/2000 sets functional requirements the model must meet, and responsibility remains with the professional.
Three limits to know before using them
The reverberation time tool returns T60 with the three historical formulations, but does not apply the judgement of UNI 11532-2:2020: comparison against reference values remains with the designer. The barrier calculation uses the dominant-screen criterion per source-receiver pair, not rigorous multi-barrier cascade, so behind successive obstacles it underestimates attenuation. The DPR 142/04 check covers road noise and not railway noise, which has a decree of its own.
On the diffraction engine, what changes between the 1996 and 2024 editions of ISO 9613-2 — and how far the numbers move — is in the dedicated note.
Try them
The tools are free and require no registration: they are all in the tools index. Reports of errors and of use cases that are not covered are useful and go to info@stline.it: that is where the corrections come from.