Separate sound decay, masking, coverage and distortion
A message may be unclear because reflections blur syllables, machinery/HVAC noise masks speech, loudspeaker coverage is uneven, the signal chain distorts or the source itself is poor. Reverberation time describes room decay; STI/STIPA describes transmission quality for speech. Neither alone identifies every cause.
Measure the quantity that can change the decision. Do not prescribe acoustic absorption before confirming that reverberation—not coverage, masking or distortion—is controlling the result.
Freeze and document the vessel-space condition
| Condition | Record | Effect |
|---|---|---|
| Geometry and finishes | Dimensions, hard/soft surfaces, ceilings, curtains and installed treatment. | Controls absorption and reflection paths. |
| Occupancy and furniture | Empty, furnished, crew/passenger state and movable items. | Can materially change decay and spatial response. |
| Openings and boundaries | Doors, hatches, curtains, partitions and adjacent coupled spaces. | Changes leakage, coupling and effective volume. |
| Vessel operation | Machinery, HVAC, cargo activity, berth/sea state and transient events. | Changes masking and measurement validity. |
Select the reverberation method for the actual space
ISO 3382-2:2008 specifies methods for reverberation-time measurement in ordinary rooms, including procedure, apparatus, measurement positions, evaluation and reporting. Vessel applicability, room geometry, coupled spaces, background noise and the contract basis still require review.
- Define interrupted-noise or impulse-response method as applicable.
- Use sufficient source and receiver positions for the selected precision and room.
- Declare decay range, frequency bands and any extrapolation.
- Check usable decay above the background-noise floor.
- Retain individual decays and spatial variation, not only one average.
Define the complete STI or STIPA transmission path
IEC 60268-16:2020 defines the STI model, test signals, measurement and prediction methods. Decide whether the test begins at an acoustic talker position, a microphone input, a system input or another agreed point. This determines which microphone, electronics, zoning, amplification, loudspeakers and room effects are included.
| Question | Source arrangement | What the result includes |
|---|---|---|
| Natural speech in a room | Calibrated acoustic source at representative talker position. | Talker-to-listener acoustic path. |
| Complete PA/GA speech path | Agreed source through microphone/input and system. | Electroacoustic chain plus room and background. |
| Loudspeaker/room performance | Defined electrical or acoustic injection point. | Downstream equipment, loudspeaker coverage and room. |
Sample the spatial experience of listeners
Select near, far, centre, edge, obstructed and complaint positions at an agreed listener height. Large public rooms, stairwells, control rooms, vehicle decks and hard-finished spaces can vary strongly. Plot results on a receiver map and keep the individual values visible.
For a PA/GA acceptance question, coordinate receiver positions with the ship PA/GA audibility and intelligibility survey so the same configuration and operating state support both decisions.
Control the limitations before interpreting STI
- Confirm test-signal level and spectrum represent the agreed use.
- Document stationary versus fluctuating background noise; IEC 60268-16 notes limitations for fluctuating noise.
- Check digital processing, compression, automatic gain control, limiters and vocoders.
- Identify echoes, impulsive noise and non-linear distortion that can affect method validity.
- Do not substitute one STI value for an application-specific acceptance criterion.
- Do not infer the treatment cause without RT, background, level distribution and system observations.
Use combined evidence to select the corrective path
| Evidence pattern | Likely controlling area | Next investigation |
|---|---|---|
| Long frequency-specific decay, weak STI, adequate level | Room reflections/reverberation. | Absorption placement and repeatable before/after RT/STI scope. |
| Shorter decay but poor STI during machinery operation | Background masking. | Noise source control, signal-to-noise and operating-condition comparison. |
| Strong position-to-position variation | Coverage, aiming, obstruction or zoning. | Receiver grid, loudspeaker mapping and system balance. |
| Poor STI close to a loudspeaker with adequate background | Signal/source distortion or processing. | Check source path, limiter, equalisation, amplifier and loudspeaker condition. |
What a defensible room-acoustics report should contain
- Space, purpose, method, applicable basis and acceptance criterion.
- Geometry, finishes, occupancy, doors and coupled-space condition.
- Machinery/HVAC state and background-noise evidence.
- Instrumentation, source arrangement, receiver map and calibration traceability.
- Frequency-band decay results and measurement-quality indicators.
- STI/STIPA results for the defined transmission path and positions.
- Spatial variation, deviations, method limitations and rejected data.
- Evidence-led corrective options and verification/retest scope.
Class, flag and acceptance context
The applicable ISO 3382 method, IEC 60268-16 procedure, vessel specification, class rule, flag requirement and criterion must be selected for the actual space and purpose. Supplier approval, survey witnessing, class notation and project-specific report acceptance are separate matters.
This guide supports planning for classed and flagged vessels. It does not claim that Vessel Doctor is approved or recognised by a society or administration.
Five items to send for a fast method review
- Vessel and space drawings with dimensions and finishes.
- Problem: echo, unclear speech, masking, coverage or acceptance.
- PA signal path, zones, messages and available equipment information.
- Representative occupancy, machinery, HVAC and door condition.
- Required RT/STI/STIPA criterion, witness and report deadline.
Onboard testing can be assessed at berth, anchorage, shipyard, dry dock, harbour trial, sea trial and in service across 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