Sound Level Distance Attenuation (Inverse Square Law)

Inspectable records

Ledger state

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

Area

Audio, Music, Photography & Color

Tranche

tranche-2

Evidence ID

t2-013

Ledger rows

1

No ledger note is attached.

Review findings

The formula is correct for an ideal omnidirectional point source in a free field. Exact ambiguity requiring review: the spec does not explicitly define the SPL reference/weighting and does not specify required distance units or the positive-distance constraint. The honest label should also mention that source directivity, near-field effects, and atmospheric absorption are excluded if those conditions matter.

Formula and scope findings

• SPL2=SPL1-20log10(d2/d1) is the standard free-field point-source relationship when both distances are positive and expressed in the same units.
• +6 dB per halving is a rounded approximation; the exact change is +6.0206 dB per halving distance.
• The specification does not explicitly state that the reference level is dB SPL measured with the same frequency weighting and bandwidth as the target level.

Unit assumptions

• Reference SPL and output are dB SPL referenced to 20 micropascals.
• Reference distance and target distance must use the same length units; only their ratio is used.
• Distances must be strictly greater than zero.
• The source is treated as an ideal point source in a free field, with unchanged source output, frequency content, and measurement conditions.

Boundary hardening

BREAK_CLAIMED · SELF_FLAGGED

The specification does not explicitly state that both reference and target distances must be strictly positive. A zero reference distance produces division by zero and an undefined logarithm, so an implementation without domain validation can fail or emit a non-finite result.

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": {
    "reference_spl_db_spl": 74,
    "reference_distance_m": 2,
    "target_distance_m": 8
  },
  "expected_outputs": {
    "target_spl_db_spl": 61.96
  },
  "working": "d2/d1 = 8/2 = 4. log10(4) = 0.60206. Distance loss = 20 x 0.60206 = 12.0412 dB. SPL2 = 74 - 12.0412 = 61.9588 dB SPL, approximately 61.96 dB SPL."
}

Related workflows

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-tranche2/tranche2-results.json
• BOUNDARY_HAZARD_CATALOG.json