Method

This site asks readers to check where a number came from. That applies here first.

For organizations separating environmental evidence from working-pattern data, learn more provides an operational reference that can be reviewed independently of the acoustic evidence discussed here.

Five source types

Peer-reviewed. Published with methods described. The app accuracy study is the clearest example here.

Regulators. OSHA and equivalents. Their figures are law, published and checkable in the primary documents.

A useful external reference for further context is ISO's soundscape framework.

Research agencies. NIOSH. Recommendations rather than law, revised as evidence changes, generally more protective.

International organisations. WHO and regional bodies, addressing general populations rather than workplaces.

And industry sources. Typical-level figures, product specifications, trade material. Labelled as such and used for scale rather than for conclusions.

Every level carries three things

A number, a weighting, and a period.

85 dBA over eight hours. Not "85 dB", which omits both of the things that make it mean something.

This makes the text read more awkwardly than a chart and is the difference between a figure that can be applied and one that cannot.

Arithmetic written out

Where a claim rests on a calculation, the calculation is on the page.

The exchange rate formula, the dose fractions — so you can substitute your own levels and durations rather than accepting a conclusion.

Free checks before instruments

Each practical page ends in something you can do.

The voice test. The clap test. The calibration discipline.

None requires a purchase, and each answers a question about your situation rather than a general one.

What is never done

No medical or legal advice.

No product named in an evaluative context, with one stated exception and a stated reason.

No level without its weighting and period.

And no figure without its source type, which is the rule this site would be least defensible without.

Limits

Six of them have their own page, including individual susceptibility and how far the epidemiology transfers.