Acoustic residual-capacity toolkit for cumulative impact assessment

Abstract

Implementation of ISO 9613-2 outdoor sound propagation and of residual acoustic capacity in the energy domain, supporting the field-capacity demonstration reported in “When environmental capacity is not a number: residual capacity and allocation in cumulative impact assessment”. The code computes octave-band sound pressure levels from source powers, sums contributions in the energy domain, and derives the residual capacity available at a receptor given a normative ceiling and an existing load. It uses the Python standard library only and reads no files. The test suite reproduces every computed claim in the accompanying paper by two routes that share no code path: five tests run the propagation model, and five recompute the same figures from four per-unit energy coefficients printed in the supplementary material, so a reader with the paper and no software can follow the same arithmetic. The suite also validates the implementation against ISO 9613-2 Table 2 across five temperature and humidity conditions, and against octave-band source spectra from regulatory assessments filed on public registers. Reproduce with python3 test_iso9613.py; expected result is 32 tests passing.