Acoustics and physics
Harmonic
Also known as harmonics, overtones.
A harmonic is an integer multiple of a fundamental frequency. A 75 Hz sonic horn radiates energy at 75 Hz (the fundamental, also called the first harmonic), with smaller amounts at 150 Hz (second harmonic), 225 Hz (third), and so on. The harmonic spectrum is what gives a real horn a richer, less pure tone than an idealised single-frequency source.
Why harmonics matter in cleaning
Most of the cleaning work is done by the fundamental, because energy is concentrated there. Harmonics extend the effective frequency content of the horn, which can be helpful where the vessel contains internals with mixed resonant characteristics — a horn nominally rated at 75 Hz also contributes some cleaning at higher harmonic frequencies useful for finer dust pockets.
Why harmonics matter in vibration analysis
Plant vibration teams analysing tube banks, fan shafts or duct supports look for energy at the horn fundamental and its harmonics. Avoiding overlap with structural resonance modes is part of multi-horn installation design.
Related terms
Related terms
- Fundamental frequencyThe fundamental frequency is the lowest natural resonant frequency of a system. For a sonic horn it is the published nameplate frequency at which the horn delivers maximum cleaning energy.
- 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).
- ResonanceResonance is the amplification that occurs when a driving frequency matches a natural mode of a system. It is exploited by sonic horns and avoided in tube-bank installation design.
- 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.