Harmonic

A harmonic is a frequency that is an integer multiple of a fundamental frequency. If a sonic horn has a 75 Hz fundamental, its harmonics occur at 150 Hz, 225 Hz, 300 Hz and so on.

Why real horns have harmonics

An ideal pure tone would contain only one frequency. Real industrial horns include driver motion, turbulent compressed-air flow, bell geometry, mounting vibration and process reflections. These effects add harmonic content and broadband sound. The fundamental usually carries the design cleaning duty, while harmonics shape the sound character and local vibration response.

Practical meaning

Harmonics can help excite smaller structures or deposits that do not respond strongly to the long fundamental wavelength. They can also affect external noise measurements because hearing-weighted sound levels may be more sensitive to higher-frequency content than to low-frequency cleaning energy. This is why a horn with the same sound-pressure level can be perceived differently depending on its spectrum.

Measurement context

Octave-band or one-third-octave measurements are more informative than a single overall dB value when evaluating acoustic cleaners. They show whether the horn is producing its expected fundamental, whether excessive high-frequency noise is present and whether structural panels are resonating. A damaged diaphragm or incorrect air pressure can shift energy away from the intended spectrum.

Troubleshooting notes

Unexpected harmonic content can be a maintenance clue. A loose mount, cracked diaphragm, worn piston, damaged bell or unstable air supply can add rattling or high-frequency components that were not present at commissioning. Conversely, a horn that has lost its fundamental may sound loud to workers but clean poorly. For this reason, acoustic troubleshooting should combine process symptoms with spectral checks and mechanical inspection instead of relying on subjective sound alone.

Measurement and plant context

A harmonic is a frequency component at an integer multiple of a fundamental frequency. In acoustics, a horn may produce a strong fundamental plus harmonics that shape the audible tone and the pressure pattern in a vessel. In electrical systems, harmonics from drives, rectifiers or furnaces can heat transformers, distort waveforms and interfere with controls. In vibration, harmonics can point to looseness, rubbing or repeated impacts.

For acoustic cleaners, harmonics are useful to understand but the cleaning design usually starts with the fundamental, sound pressure and vessel geometry. A measured spectrum with new or missing harmonics can indicate a damaged diaphragm, blocked horn throat, changed air pressure or a structural resonance. Noise assessments should consider harmonic content because higher components can be more noticeable to workers even when the fundamental carries the cleaning energy.

Troubleshooting use

Harmonic patterns help separate a normal tone from a developing fault. In acoustic equipment, a weakened or distorted harmonic pattern can point to a cracked diaphragm, damaged piston, blocked throat or changed air supply. In rotating equipment, harmonics of running speed can suggest looseness, rubbing or structural resonance. In electrical systems, harmonic distortion can come from variable-speed drives, rectifiers, arc furnaces or large non-linear loads.

The practical rule is to interpret harmonics with the physical system. A harmonic peak is not automatically a problem; it becomes important when it aligns with a resonance, increases over time, creates noise exposure, overheats equipment or correlates with poor cleaning performance.

Trend history is often more useful than a single spectrum.