Acoustics and physics
Wavelength
Also known as acoustic wavelength, sound wavelength.
Wavelength is the spatial distance over which one full cycle of a wave repeats. It is calculated as λ = c / f, where c is the speed of sound in the medium (~343 m/s in air at 20 °C) and f is the frequency in hertz. For industrial acoustic cleaning the wavelength is the single most informative dimension because it predicts how the horn's sound field will fill the vessel.
Wavelengths for industrial sonic horns
| Frequency | Wavelength in air at 20 °C |
|---|---|
| 12 Hz | ~28 m |
| 30 Hz | ~11 m |
| 60 Hz | ~5.7 m |
| 75 Hz | ~4.6 m |
| 125 Hz | ~2.7 m |
| 230 Hz | ~1.5 m |
| 400 Hz | ~0.85 m |
Wavelengths in hot flue gas are longer than in cool air because the speed of sound rises with temperature — at 200 °C the speed of sound is about 436 m/s, stretching a 75 Hz wave to roughly 5.8 m.
Why long wavelengths penetrate further
Acoustic energy diffracts efficiently around obstructions smaller than its wavelength. A 5-metre 60 Hz wave bends around tube rows, electrode spacings and baffles that would scatter or absorb a 1-metre 350 Hz wave. This is the underlying physics of why low-frequency acoustic cleaners clean large open vessels better than high-frequency units.
Related terms
Related terms
- 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 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.
- Standing waveA standing wave is a stationary interference pattern that creates nodes (zero pressure, low cleaning) and antinodes (peak pressure, high cleaning). Horn placement is designed to minimise dead zones.
- Low-frequency acoustic cleanerLow-frequency acoustic cleaners operate at 60–250 Hz. The long wavelength penetrates deep into large open vessels such as ESPs, recovery boilers and cement preheater cyclones.
- High-frequency acoustic cleanerHigh-frequency acoustic cleaners operate at 250–450 Hz. The shorter wavelength carries more energy per unit volume and suits fabric filters, SCR catalysts and small hopper geometries.