Acoustic Ray Analysis

Benchmarking against the PTB Round Robin III studio case has produced encouraging results. We are preparing the detailed findings, including the tested configuration and limitations, for publication. Review the benchmark status and evidence scope when interpreting these results.

Inputs and calculation scope#

Selected Revit geometry, including the intended phase, links, categories and analysis scope.
Source position, orientation, spectrum, directivity and defined level basis.
Listening positions and their relationship to the physical room.
Surface absorption, scattering and atmospheric conditions.

The calculation follows sound-energy propagation and surface interactions, applies atmospheric attenuation and collects arriving energy at receiver positions. Direct sound is evaluated separately when a direct path is available. The result is an energy-time response for each position in eight octave bands: 63, 125, 250, 500, 1,000, 2,000, 4,000 and 8,000 Hz.

Propagation and surface interactions#

Propagation time

t = \frac{ℓ}{c}

Arrival timing depends on the path length and the sound speed used in the calculation.

t: Travel time (s)
ℓ: Sound-path length (m)
c: Sound speed (m/s)

ISO 9613-1:1993 — calculation of atmospheric absorption.

Surface absorption energy balance

E_{reflected} = (1 - α) \cdot E_{incident}

Surface absorption removes a fraction of incident band energy; the remainder is reflected. Transmission through the construction is excluded.

E: Incident or reflected band energy (consistent energy unit)
α: Effective energy absorption coefficient between zero and one (dimensionless)

C. F. Eyring (1930), Reverberation Time in “Dead” Rooms.

Specular reflection follows the mirror-reflection direction. Scattering redistributes reflected energy among other directions; it does not create additional sound energy. The effective absorption used in the energy balance must lie between zero and one even where a material's measured equivalent absorption coefficient exceeds one.

Atmospheric attenuation#

Atmospheric attenuation of energy

E (ℓ) = E_{0} \cdot 10^{\frac{- a \cdot ℓ}{10}}

Atmospheric attenuation reduces sound energy along a propagation path according to the frequency band and entered conditions.

E(ℓ), E₀: Remaining and initial band energy (consistent energy unit)
a: Band atmospheric attenuation for the entered conditions (dB/m)
ℓ: Propagation length (m)

ISO 9613-1:1993 — calculation of atmospheric absorption.

Atmospheric loss varies with frequency, temperature, humidity and pressure. Sound-speed and attenuation assumptions belong to the saved calculation context. Review those inputs rather than assuming the statistical Room Analysis constant applies to every ray calculation.

From arriving energy to results#

Metrics are calculated from receiver energy-time responses. See Acoustic results and their definitions for decay, clarity, levels and speech qualifications.

The calculation checks numerical support for requested outputs within workload limits. Results also carry qualifications for incomplete response and other limitations. Numerical support concerns the calculation's evidence; it does not establish agreement with a measured room.

Physical limitations#

Geometrical acoustics does not model low-frequency modes, coherent interference, diffraction, construction transmission or flanking paths. Small-scale geometry relative to wavelength, missing surfaces and uncertain material inputs can limit physical applicability.

Review the validation status and limitations for the scope of available evidence. Decay evidence does not automatically validate clarity, sound levels, speech or listening previews.