Reverb Time RT60 (Sabine Formula) implementation

Binding contract

This record describes what an executable surface must bind and validate. It does not claim that a public calculator, package, or production route is deployed.

Record owner

Guth Instruments

Lifecycle

verified-clean

Evidence ID

t7-010

Effect

Computation or source lookup only

Input and validation requirements

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.

Required corrections

No binding erratum is attached to this unique-name record. Implementers must still preserve the declared units, domain, and failure behavior.

Inspectable interface fixture

The sample below is evidence for interface and validation tests, not a production implementation.

{
  "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."
}

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