1. Keep audibility, intelligibility and reverberation as separate decisions
A listener can detect an alarm yet fail to recognise its pattern. A spoken announcement can be audible but still lose consonants and meaning. A room can have long sound decay without the PA/GA system itself being defective. Define which decision the owner, yard, integrator, class or flag reviewer needs before selecting points, signals or criteria.
| Question | Primary evidence | Do not substitute |
|---|---|---|
| Can the alert be heard and recognised? | Specified alert, background-noise condition, receiver level and coverage record. | A quiet-space spot reading. |
| Can the spoken message be understood? | Representative speech path, STI/STIPA or agreed alternative, level and noise context. | Sound pressure level alone. |
| Does the room retain sound too long? | Reverberation-time measurement with room, source, receiver and decay-quality records. | A PA-system intelligibility score alone. |
Use the canonical ship PA/GA audibility survey for system coverage and alarm or announcement decisions. Use onboard reverberation and speech-intelligibility testing when room decay, masking or transmission quality must be separated.
2. Freeze the representative operating baseline
Record whether the vessel is at berth, anchorage, commissioning, harbour trial, sea trial or in service. For every run, capture propulsion and generator state, ventilation fans, pumps, thrusters, cargo equipment, doors, fire doors, dampers, weather openings, occupancy and other dominant noise sources. A system that passes in an artificially quiet condition may not answer the operational question.
| Run / time | Vessel condition | Machinery / ventilation | Doors / occupancy | Signal / message | Level controls | Deviation |
|---|---|---|---|---|---|---|
| RUN-___ | ___ | ___ | ___ | Alarm / speech / test signal | Normal / override / ___ | ___ |
| RUN-___ | ___ | ___ | ___ | Alarm / speech / test signal | Normal / override / ___ | ___ |
3. Build a receiver map that can expose weak coverage
Group cabins, corridors, stairways, machinery spaces, control rooms, workshops, galleys, stores and open decks by use, geometry, background noise and loudspeaker arrangement. Record deck, frame or room reference; listener height; distance and orientation to the loudspeaker; obstruction; local reflective surfaces; and nearby noise source. Include boundaries and known shadow zones rather than measuring only convenient centre points.
The PA/GA commissioning test plan gives the full planning sequence. This comparison guide provides the field decision record without replacing the governing ship-specific acceptance basis.
4. Record audibility and alert recognisability without inventing a universal margin
Measure the agreed alert or announcement under its defined system state and representative ambient condition. State the level quantity, time response, duration, microphone position and whether competing intermittent noise was present. Apply only the criterion identified by the controlling SOLAS, LSA Code, flag, class, contract, maker or project document. A difference between two measured levels is not automatically a universal pass margin.
5. Treat STI or STIPA as a controlled speech-transmission measurement
IEC 60268-16:2020 defines objective rating of speech intelligibility by speech transmission index. Identify the method, signal source and injection path, talker or microphone chain, loudspeaker zone, receiver location, background-noise treatment, test level, number of measurements, instrument and software version, calibration or field checks and any validity warning.
A high test-signal level can mask a coverage problem, while a low or unstable source can understate system capability. Report the measured conditions and project criterion separately. The detailed reverberation, STI and STIPA measurement guide covers method selection and receiver sampling.
6. Measure room decay when reflections are part of the problem
Reverberation can smear successive syllables, especially in hard-finished machinery, stair, vehicle and large public spaces. ISO 3382-2:2008 specifies reverberation-time measurement in ordinary rooms. Record room condition, furnishing and occupancy, source and receiver locations, method, frequency bands, decay range, background-noise limit, repeatability and any non-linear or interrupted decay.
| Point | Space / listener | System zone / speaker | Ambient condition | Level / STI-STIPA / RT | Validity | Photo / plan |
|---|---|---|---|---|---|---|
| RX-___ | ___ | ___ | ___ | ___ | Valid / repeat / qualified | REF-___ |
| RX-___ | ___ | ___ | ___ | ___ | Valid / repeat / qualified | REF-___ |
7. Diagnose source, transmission path and receiver before changing level
If results vary, separate microphone or message source, processing, priority logic, amplifier or loop, cabling, loudspeaker, zoning, coverage geometry, background-noise masking and room response. Compare adjacent receivers and zones; inspect polarity, aiming, obstruction and damaged devices; and repeat selected measurements while one controlled variable changes. Raising gain everywhere can increase distortion, feedback or excessive level without fixing the weak receiver.
| Observed symptom | Useful comparison | Boundary |
|---|---|---|
| Loud but unclear throughout one zone | Source path, processing, distortion, STI and ambient noise. | Do not blame reverberation without room evidence. |
| Weak only behind an obstruction or boundary | Adjacent receiver levels, speaker geometry and zone state. | A global gain change may create excessive levels elsewhere. |
| Clear when quiet, poor during one machinery state | Matched ambient spectrum and speech result with that source on/off. | The symptom does not identify the corrective owner. |
| Long echo with stable system output | Room decay by band and listener position. | Treatment feasibility needs separate design review. |
8. Release a report that a reviewer can reproduce
- Identify vessel, system configuration, zones, tested signals and governing document, edition and clause supplied by the project.
- Link every value to a point, time, operating condition, instrument, setup and validity decision.
- Separate alert audibility, speech intelligibility, room reverberation and functional-system observations.
- Show unavailable spaces, failed runs, deviations, uncertainty or variability and untested alternatives.
- State measured facts, interpretation, recommendations and acceptance responsibility separately.
A report may support owner, yard, class or flag review, but the relevant reviewer controls acceptance. IACS does not approve service companies, and this guide does not claim Vessel Doctor is class- or flag-approved, authorised, locally based in every market or able to guarantee attendance or acceptance.
9. Match the retest and prepare only permissioned case proof
Before adjustment or repair, freeze receiver points, signal path, system settings, machinery state, ambient condition, doors, occupancy, method and output metrics. On retest, list every difference. Publish a case only with contemporaneous evidence and written permission, and remove vessel and customer identifiers as agreed.
| Baseline | Finding boundary | Approved action | Matched condition | Result / limitation | Permission |
|---|---|---|---|---|---|
| Points / setup / condition | Supported and untested causes | ___ | Same / difference listed | ___ | Owner / scope / date |
This blank record is not a customer result. Do not add a vessel, yard, class, flag, numerical improvement, pass statement or testimonial without verified project evidence and publication authority.
10. Confirm current project documents
- IEC 60268-16:2020 — objective rating of speech intelligibility by speech transmission index; the IEC copy includes Corrigendum 1:2025.
- ISO 3382-2:2008 — reverberation-time measurement in ordinary rooms; ISO confirms this edition remains current.
- IMO resolution A.1204(34) — Code on Alerts and Indicators, 2025, adopted 3 December 2025; it revokes resolution A.1021(26).
Official records establish document identity and broad scope, not the criterion for every ship. Confirm current amendments, vessel type, contract, system specification, class rules, flag instructions and witness requirements before attendance.