Glossary
Controls and ancillaries
Sound-attenuation enclosure (sonic horn)
Also known as sound enclosure, acoustic enclosure, noise-attenuation enclosure.
A sound-attenuation enclosure surrounds a sonic horn installation to reduce the external SPL experienced at the operator station, walkways and plant boundary. Typical SPL reduction is 10–25 dB depending on enclosure design — significant enough to bring exposures within OSHA and EU 2003/10/EC action limits at most realistic operator distances.
When enclosures are specified
- Sonic horns mounted close to operator-access walkways or maintenance positions
- Multi-horn arrays where cumulative SPL exceeds the limit even at modest distance
- Plant boundaries close to residential or commercial property
- Indoor installations where reflection raises ambient SPL
Trade-offs
- Cost — enclosures typically add 10–20% to the installed cost of the horn system
- Maintenance access — must be designed to allow routine diaphragm replacement and inspection
- Thermal management — for hot-side installations, enclosure ventilation must prevent overheating of accessories
- Slight SPL reduction inside the vessel — usually marginal, but worth checking in marginal-coverage cases
Related terms
Related terms
- Sonic hornA sonic horn is a pneumatically-driven low-frequency sound emitter (typically 60–400 Hz at 140–180 dB SPL) used to dislodge particulate fouling from boilers, ESPs, baghouses and process vessels.
- Sound pressure levelSPL is the logarithmic measure of sound pressure in decibels relative to a 20 µPa reference. Industrial sonic horns operate at 140–180 dB SPL.
- OSHA 29 CFR 1910.95OSHA 29 CFR 1910.95 sets US occupational noise exposure limits. The action level is 85 dBA TWA; the permissible exposure limit is 90 dBA TWA. Calculated from time-weighted average exposure.
- EU Directive 2003/10/ECEU Directive 2003/10/EC sets noise-exposure limits for EU workplaces. Lower action 80 dBA, upper action 85 dBA, exposure limit 87 dBA, all daily averages.