Source: https://guthlabs.ai/docs/instruments/reverb-time-rt60-sabine-formula/

instrument / verified-clean

# Reverb Time RT60 (Sabine Formula)

The current ledger marks this instrument verified clean within the source-bound verification corpus.

Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**

## Inspectable records

[01**Overview**Purpose and lifecycle](<https://guthlabs.ai/docs/instruments/reverb-time-rt60-sabine-formula/>)[02**Mechanism**Method and assumptions](<https://guthlabs.ai/docs/instruments/reverb-time-rt60-sabine-formula/mechanism/>)[03**Implementation**Binding and validation](<https://guthlabs.ai/docs/instruments/reverb-time-rt60-sabine-formula/implementation/>)[04**Qualification**Evidence and errata](<https://guthlabs.ai/docs/instruments/reverb-time-rt60-sabine-formula/qualification/>)

## Ledger state

The current ledger marks this instrument verified clean within the source-bound verification corpus.

**Area**: Audio, Music, Photography & Color

**Tranche**: tranche-7

**Evidence ID**: t7-010

**Ledger rows**: 1

No ledger note is attached.

## Review findings

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.

### Formula and scope findings

- 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.

### Unit assumptions

- 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.

## Boundary hardening

**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.

## Errata and corrections

No applied erratum is attached to this unique-name record.

## Inspectable example

4 review vectors are recorded. One source-bound sample is shown below.

````
{
  "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."
}
````

## Related workflows

No source-defined multi-instrument workflow membership is recorded.

## Sources and evidence

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

- `VERIFIED_LEDGER.json · VERIFIED_CLEAN`

- `evidence-tranche7/tranche7-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`