546.1 Noise sources

HPUs, fans, pumps, and contactors dominate. Identifying sources focuses HVM bollard mitigation (512–513).

Start by mapping every contributor: the HPU motor and pump, cooling fans inside enclosures, contactor/relay clacks, and fluid-borne pulsing in hoses. For electromechanical drives, gearbox whine and PWM-driven motor tones appear. Structure-borne paths (mountings, slab, cabinets) can amplify “drumming.” Listing sources allows targeted fixes rather than blanket, costly treatments.

Classify sounds into continuous (e.g., fan hum), intermittent (start/stop), and impulsive (contactors). Note duty pattern: operations per hour affect annoyance more than peak level alone. Where lanes are near receptors (residential, hotel drop-offs), coordinate with Hot Climate Design (avoid oversized fans) and with Electromechanical Drives for their different spectral signatures.

546.2 Local limits & guidance

Document site limits and test methods. Compliance protects crash rated bollard projects from complaints (133).

Agree the applicable rules early: municipal daytime/night-time limits, façade-point vs boundary-point measurements, and special conditions for healthcare or hospitality. In the UAE, approvals often require demonstrating “no nuisance” near receptors; if SIRA is in scope, cross-reference the security submission while noting that acoustic compliance is a separate planning condition—see SIRA Bollards (UAE). Record the limit values in the specification, including “curfew” windows and penalties for exceedance, and tie them to witness tests (638).

546.3 Measurement methods

Use calibrated meters, A-weighting, and fixed distances. Consistency keeps HVM bollard data credible (638).

Use a Class 1 meter with valid calibration. Report A-weighting (dBA) for compliance and note the time-weighting (Fast/Slow). Fix the microphone height and distance (e.g., 1.5 m above ground, 1 m from enclosure face, or property boundary) and document background noise and wind/temperature. Capture both steady-state (fan on) and operational peaks (raise/lower cycle). Keep photos, GPS tags, and logger files in the witness forms for audit.

546.4 Design for quiet

Pick low-noise pumps, soft mounts, and tuned flow. Quiet details preserve crash rated bollard acceptance (341).

Specify low-noise motors/pumps and operate away from resonances. Reduce pressure ripple with accumulators and tuned hose lengths; avoid sharp bends and cavitation. Choose larger, slower fans where practical, and select blade profiles with better tonal balance. Keep laminar intake/exhaust paths and avoid grille whistle. Use supply quality that avoids brownout-induced motor chatter. For drive systems, PWM settings and ramps can reduce tonal spikes.

546.5 Barriers & lining

Add acoustic lining and screens with airflow (348). Barriers reduce HVM bollard emissions.

Acoustic screens and cabinets work when they block line-of-sight and add absorption. Line interior panels with acoustic lining rated for heat and oil mist. Maintain free area and baffles so cooling air still flows; choking the airflow just raises fan speeds and overall noise. Where receivers are above-grade (e.g., hotel rooms), raise the screen crest or adjust placement per Panel Siting & Access to maximize shielding.

546.6 Vibration isolation

Isolate HPUs, route hoses to avoid drumming. Isolation lowers crash rated bollard noise (512).

Break structure-borne noise paths using elastomeric or spring mounts tuned below the running speed and its harmonics. Fit flexible connections, avoid rigidly fixing panels to resonant slabs, and route hoses to prevent panel “drumming.” Keep isolation consistent across anchor points; one hard short-circuit can defeat the whole system. Verify with a quick accelerometer scan during commissioning and correct obvious peaks (re-torque, add damping mass, re-route hoses).

546.7 Night mode/curfew

Slow cycles, dim beacons, and restrict alarms (525). Night modes keep HVM bollard neighbors onside.

Implement a “night mode” that reduces operations per hour, softens ramps, and limits audible alarms. Where safe, favor visual beacons over horns (see Safety Signalling) and use night auto-dimming. Tie curfew windows to the site’s modes of operation with clear operator prompts and logs. Document exceptions (e.g., EFO) so security is never compromised.

546.8 Acceptance testing

Witness day/night levels with photos and logs (638). Tests close crash rated bollard conditions.

In SAT, repeat measurements in day and night ambient conditions. Log the exact system state (fan speed, cycle profile), microphone position, and weather. Capture evidence in the SAT / Witness Procedure with a witness form, COS logs, and photographs. Flag any exceedances as NCRs and retest after mitigation. Keep the acoustic report in the Handover Pack.

546.9 Maintenance impacts

Plan lining inspection/cleaning. Care keeps HVM bollard noise low (365).

Acoustic fixes drift without maintenance. Add lining inspection/cleaning to the maintenance plan, check fans for bearing wear/imbalance, and verify mount integrity at service intervals. Replace clogged filters and damaged seals that trigger cavitation hiss. Revalidate noise annually or after equipment swaps; capture results in the asset register and update the change log so acoustic compliance remains demonstrable.

546 Acoustic limits for HVM Bollards HPUs/enclosures — FAQ