Infrasound

Professional Definition

Infrasound is sound whose spectrum lies in the frequency range from 1 Hz to 20 Hz.

From a physical point of view, these are acoustic waves with very long wavelengths (even up to several meters), which are below the threshold of hearing of the average human. Due to their low frequency, these waves poorly attenuate in the air, allowing them to propagate over significant distances without much loss of energy. In acoustic engineering, the analysis of infrasound is crucial for assessing the impact of wind turbines, heavy transport, or ventilation systems on building structures and people's well-being.

Acoustics in Simple Words

Imagine standing on the beach. A typical sound (e.g., a whistle) consists of fast, tiny waves hitting the shore. Infrasound, on the other hand, resembles a slow, powerful ocean surge. Although you do not hear the wave striking (because the pressure change occurs too slowly for your ear), you can feel the water lifting and lowering you. In a similar way, infrasound generated by, for example, a passing truck – you may not always hear the low tone itself, but you feel the vibration of the windows or pressure in your chest.

Summary

Infrasound is acoustic waves below 20 Hz, inaudible to the ear, but felt by the body as vibrations. Their sources are natural phenomena (e.g., storms) and technical ones (machines). Due to weak attenuation, they pose a challenge in terms of vibro-acoustic insulation in buildings.