Acoustics and physics
Sound power vs sound pressure
Also known as sound power, sound power level, PWL vs SPL.
Sound power is the total acoustic energy a source emits per unit time, measured in watts. It is an intrinsic property of the source and does not change with listener distance. Sound pressure is the local pressure fluctuation at a measurement point, measured in pascals (and reported in decibels as SPL). Pressure falls with distance per the inverse-square law; power does not.
Why both matter for a sonic horn
Vendor datasheets normally publish SPL at 1 m on the bell axis, because that is what specifiers compare. But two horns with identical 150 dB nameplate SPL can radiate different sound power if their directivity differs — a wider radiation pattern delivers more useful energy into the vessel. Sound power level (PWL) is the comparable metric when evaluating total cleaning energy, measured per ISO 9614.
Practical rule of thumb
For noise-exposure work at the operator station, use SPL with distance corrections. For cleaning-coverage modelling inside the vessel, sound power and directivity are the more useful inputs.
Related terms
Related terms
- 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.
- 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.
- 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.
- ISO 9614ISO 9614 series specifies methods for determining sound-power levels from sound-intensity measurements. The reference method for comparing total acoustic output of sonic horns.