How we approach the work
Low-frequency phenomena may be intermittent, poorly represented by overall indicators and influenced by airborne, structural or ground-borne transmission. Investigation should preserve time and frequency information and relate it to what occurs on site.
01
When to consider this investigation
- Perceived hum, pulsing or pressure sensation of uncertain origin.
- Events linked to ventilation, pumping, motors, transformers, traffic or rotating equipment.
- Phenomena more noticeable at night or in quiet indoor environments.
- Cases where overall levels do not explain the reported perception.
- Suspected structural component or correlation with vibration.
02
Analysis methodology
- Time recording with resolution suited to the event.
- Band and FFT analysis to locate dominant components.
- Event identification and comparison of periods with and without occurrence.
- Assessment of repeatability, duration, modulation and operating context.
- Reasoned exclusion of electrical, environmental or unrelated events.
03
Simultaneous vibration measurement
- Time synchronisation between acoustic and vibration channels.
- Comparison of events to identify correspondence between sound and vibration.
- Support in distinguishing predominantly airborne propagation from a structural component.
- Guidance for further measurements near the source or along the transmission path.
04
Technical framework
- The assessment criterion and frequency range are selected for the case, site and objective.
- Suitable international technical references may be considered without replacing the applicable legal framework.
- The lack of a single universal indicator makes transparency about method, limitations and evidence essential.