Acoustics and physics
Decibel
Also known as dB, decibels.
The decibel (dB) is a logarithmic unit used to express the ratio between two values of an acoustic quantity — most commonly sound pressure, sound intensity or sound power. A 10 dB increase represents a tenfold increase in intensity and a perceived roughly doubled loudness. A 3 dB increase represents a doubling of intensity.
Why a logarithmic scale
Human hearing — and the practical range of industrial acoustic cleaning — spans more than ten orders of magnitude of sound pressure (20 µPa to several hundred Pa). A linear scale would be unwieldy. The logarithmic decibel compresses this into a tractable 0–180 dB band and aligns with how the ear actually responds to intensity changes.
Reference points
| Value | Meaning |
|---|---|
| +3 dB | Sound intensity doubled |
| +10 dB | Sound intensity ×10; perceived loudness roughly doubled |
| +20 dB | Sound intensity ×100 |
| 0 dB SPL | Reference threshold of hearing (20 µPa) |
| 140 dB SPL | Lower end of industrial sonic horn output |
| 180 dB SPL | Upper end of pneumatic industrial cleaning horns |
Weighting
For noise-exposure work, raw dB is often weighted to better reflect human hearing. A-weighting (dBA) is the standard for occupational-noise calculations under OSHA 29 CFR 1910.95 and EU Directive 2003/10/EC. C-weighting (dBC) is used for peak exposure to high-level impulsive sound.
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.
- 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).
- 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.
- Octave bandAn octave band is a frequency range where the upper bound is twice the lower. Octave-band SPL data is the standard format for noise-exposure analysis under OSHA and EU 2003/10/EC.