Acoustics and physics
Sound pressure level
Also known as SPL, sound pressure level dB.
Sound pressure level (SPL) is the logarithmic measure of sound pressure relative to the 20 µPa human-hearing reference, expressed in decibels. It is the primary specification figure for any sonic horn or acoustic cleaner and the metric used to size noise-exposure controls at the work area.
Industrial reference values
| SPL (dB) | Reference |
|---|---|
| 0 | Threshold of human hearing |
| 60 | Normal conversation |
| 120 | Threshold of pain |
| 140 | Industrial sonic horn (lower-output models) |
| 160 | Typical cement / ESP sonic horn |
| 180 | Upper limit of pneumatic industrial sonic horns |
| 194 | Theoretical maximum for an undistorted sine wave in air |
SPL and cleaning effectiveness
Cleaning energy scales with intensity, which doubles for every 3 dB rise. A 150 dB horn delivers roughly twice the energy of a 147 dB horn at the same distance. SPL is not, however, the only selection criterion: frequency determines wavelength and therefore penetration. A 150 dB low-frequency horn typically out-cleans a 160 dB high-frequency horn in a large open vessel.
SPL and exposure
Reported nameplate SPL is measured at 1 m on the bell axis. Real exposure at the work area falls with distance per the inverse-square law and through enclosure attenuation. Compliance with OSHA 29 CFR 1910.95 and EU Directive 2003/10/EC is calculated from exposure, not from nameplate SPL.
Related terms
Related terms
- DecibelThe decibel is a logarithmic ratio used to express sound pressure, sound intensity and sound power. A 10 dB rise represents a tenfold rise in intensity.
- FrequencyFrequency is the number of acoustic cycles per second, measured in hertz. Industrial acoustic cleaners operate at 12–30 Hz (infrasonic), 60–250 Hz (low) or 250–450 Hz (high).
- Sound power vs sound pressureSound power is the total acoustic energy a source emits per second and is a property of the source. Sound pressure is what a microphone measures at a point and falls with distance.
- Inverse-square lawIn free-field conditions sound intensity falls as 1/r². Sound pressure level drops by approximately 6 dB for each doubling of distance from the source.
- 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.