Reverb Time RT60 (Sabine Formula) mechanism

Model scope

The arithmetic and core Sabine algorithm are correct under the stated SI and diffuse-field assumptions. Verdict is NEEDS_REVIEW because the claimed per-band output lacks an explicit band schema and the lookup-table convention is underspecified: absorption coefficients depend on frequency, mounting, and measurement convention. The existing honest-label warning is appropriate but should also mention air absorption, non-diffuse geometry, and the need to reject A=0.

• RT60=0.161*V/A is the standard metric Sabine approximation when V is in m^3, surface areas are in m^2, and A is in metric sabins (m^2 equivalent absorption).
• The stated per-band output requires absorption coefficients specified for an explicit octave or one-third-octave frequency band; the spec does not define the supported bands.
• The Sabine approximation assumes a sufficiently diffuse field and relatively low-to-moderate average absorption. It becomes unreliable in very live, very dead, highly non-diffuse, or strongly coupled rooms.
• The coefficient 0.161 is a rounded SI constant; implementations should document whether they use 0.161 exactly or a higher-precision constant.

Units and conventions

• Room volume V is in cubic metres (m^3).
• Surface areas Si are in square metres (m^2).
• Absorption coefficients alpha_i are dimensionless, frequency-specific random-incidence coefficients, normally between 0 and 1 for ordinary material data.
• A=Σ(Si*alpha_i) is in metric sabins, numerically m^2 equivalent absorption.
• All listed surfaces are non-overlapping room boundaries; openings, occupants, furniture, air absorption, and coupled rooms are not included unless separately modeled.
• The supplied material coefficients are treated as exact lookup values for the test calculations, although real coefficients vary with frequency, mounting, incidence, and test method.

Inspectable vector

One of 4 source-bound review vectors:

{
  "inputs": {
    "volume_m3": 180,
    "frequency_band_hz": "500 octave band",
    "surfaces": [
      {
        "material": "carpet on floor",
        "area_m2": 60,
        "absorption_coefficient": 0.3
      },
      {
        "material": "acoustic ceiling tile",
        "area_m2": 60,
        "absorption_coefficient": 0.6
      },
      {
        "material": "painted drywall walls",
        "area_m2": 120,
        "absorption_coefficient": 0.1
      }
    ]
  },
  "expected_outputs": {
    "equivalent_absorption_A_m2": 66,
    "RT60_s": 0.4390909091
  },
  "reference_data": {
    "carpet_on_floor_500Hz": {
      "absorption_coefficient": 0.3,
      "source_convention": "widely tabulated standard value in architectural-acoustics octave-band coefficient tables"
    },
    "acoustic_ceiling_tile_500Hz": {
      "absorption_coefficient": 0.6,
      "source_convention": "widely tabulated standard value in architectural-acoustics octave-band coefficient tables"
    },
    "painted_drywall_500Hz": {
      "absorption_coefficient": 0.1,
      "source_convention": "widely tabulated standard value in architectural-acoustics octave-band coefficient tables"
    }
  },
  "working": "A=(60*0.30)+(60*0.60)+(120*0.10)=18+36+12=66 m^2. Numerator=0.161*180=28.98. RT60=28.98/66=0.4390909091 s."
}

Failure boundary

BREAK_CLAIMED · SELF_FLAGGED

The zero-absorption case produces division by zero and must be rejected or represented as undefined/infinite. The specification also provides no defined branch behavior for absorption coefficients outside the conventional table range or for Sabine-model validity limits.

Other records

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json
• evidence-tranche7/tranche7-results.json
• BOUNDARY_HAZARD_CATALOG.json