Define audibility, intelligibility and acceptance separately
Audibility asks whether a signal can be heard or recognised at the receiver. Speech intelligibility asks whether spoken information can be understood through the microphone, processing, amplifier, zoning, loudspeaker and acoustic space. Commissioning, newbuilding acceptance, retrofit verification and complaint troubleshooting can require different evidence.
Write the spaces, signal type, operating condition, approved plan or specification, evaluation criterion, witness and report-review route before testing begins.
Freeze and record the complete PA/GA configuration
| Element | Record | Why it matters |
|---|---|---|
| Source | Live microphone, recorded message, tone generator or approved test source. | Different sources exercise different parts of the signal chain. |
| Processing and amplification | Rack, amplifier, gain, equalisation, limiter, priority and fault state. | A changed setting can invalidate before/after comparison. |
| Zoning | Selected zones, isolations, muting, overrides and redundant path. | A coverage defect may be a configuration problem rather than a loudspeaker problem. |
| Receivers | Loudspeaker identity, tap/setting where available, orientation and physical condition. | Supports targeted corrective work and retest. |
Map receiver positions from risk and use—not convenience
Use approved drawings, zone schedules and vessel-space use to select representative cabins, alleyways, stairways, public rooms, control stations, machinery spaces, workshops, vehicle/cargo decks and open decks where applicable. Add complaint positions, coverage boundaries, obstructed locations and high-background-noise areas.
- Give each receiver position a stable identifier and drawing reference.
- Record measurement height and microphone orientation required by the agreed method.
- Cover near, far, edge and transition positions within each relevant zone.
- Separate occupied-space speech tests from tone or alarm measurements.
- Document inaccessible, unsafe or unavailable positions as limitations.
Test under the representative vessel operating condition
Background noise can change with propulsion, generators, ventilation, pumps, cargo systems, thrusters, doors, weather and activity. A quiet-ship reading may not represent service conditions. Record machinery combinations, RPM/load, HVAC state, openings, vessel location and unusual transient events.
Measure background using a declared quantity, duration and instrument arrangement. IEC 61672-1 specifies performance requirements for sound level meters; the required class and verification evidence still depend on the governing project basis.
Use the measurement that answers each question
| Question | Evidence | Caution |
|---|---|---|
| Can the warning signal be heard? | Representative background and alarm/tone levels, signal character and receiver map. | Use the required comparison or criterion; do not invent one generic margin. |
| Can the spoken message be understood? | Agreed STI/STIPA or other method across the intended transmission path. | Loudness alone does not establish intelligibility. |
| Is coverage spatially uniform? | Level and intelligibility distribution across a documented receiver grid. | One convenient point can miss dead zones and excessive hot spots. |
| Did repair or retrofit work? | Repeat the same source, configuration, positions and operating state. | Changed gain, doors or background can invalidate comparison. |
IEC 60268-16:2020 defines the STI model and measurement/prediction methods but does not itself provide certification criteria for every voice-alarm application. The acceptance value must come from the applicable vessel rule, specification or agreed review basis.
Diagnose the controlling cause before changing gain
| Problem | Check | Possible action route |
|---|---|---|
| Alarm cannot be heard in one area | Zone state, loudspeaker operation, background, obstruction and level distribution. | Restore coverage or correct the local masking source. |
| Announcement is loud but unclear | Reverberation and speech-intelligibility testing, distortion, source quality and aiming. | Do not increase level automatically; treat the dominant limitation. |
| Intermittent or missing zone | Priority, switching, supervision, amplifier/channel and cable/path evidence. | Electrical/system investigation may be required beyond acoustic measurement. |
| Near positions are excessive, far positions fail | Speaker distribution, aiming, tap balance, obstruction and acoustic decay. | Rebalance coverage rather than relying on global gain. |
What a review-ready PA/GA report should contain
- Vessel, survey purpose, applicable basis, drawings and attendance parties.
- System configuration, source path, zones and equipment state.
- Receiver-position schedule and marked plan.
- Machinery, HVAC, doors, weather and vessel operating condition.
- Instrumentation, serial numbers, settings and calibration traceability.
- Background, alarm/announcement and intelligibility results with declared quantities.
- Evaluation status, deviations, inaccessible positions and limitations.
- Defect localisation, corrective priorities and exact verification scope.
Class, flag and supplier-qualification context
The 2009 IMO Code on Alerts and Indicators was adopted by resolution A.1021(26); IMO approved a draft updated Code in 2025 for subsequent adoption. Confirm which instruments, class rules, approved plans and contract editions apply to the vessel. Supplier qualification and project-specific report acceptance are separate decisions.
For ABS-, BV-, CCS-, CRS-, DNV-, IRS-, KR-, LR-, ClassNK-, PRS-, RINA- or Türk Loydu-classed vessels and relevant flags, confirm requirements with the owner, yard and attending surveyor. This guide makes no approval or guaranteed-acceptance claim.
Five items to send for a fast feasibility review
- Vessel, type, IMO number and attendance location/window.
- PA/GA drawings, zone schedule and approved test requirement.
- Signal/message, language and source path to be tested.
- Representative operating condition and critical spaces.
- Witness, report-review route and acceptance deadline.
Attendance can be assessed in Singapore, Malaysia, India, Sri Lanka, Indonesia, Thailand, the Philippines, the Middle East, Asia-Pacific and worldwide, subject to access and availability.
Turn the communication problem into a controlled onboard scope.
Send the vessel, drawings, operating condition, affected spaces, applicable basis and report deadline. The scope will define the measurement route and evidence before mobilisation.
Review the canonical serviceRequest a technical scope