The belief that inaudible sounds have no effect on humans has been disproven by the results of a recent study conducted in Canada. Researchers found that infrasound—sound waves with frequencies below 20 hertz, which the human ear cannot detect—can cause irritation, physiological stress, and alter the emotional perception of music, making it seem sadder and more melancholic.

The Nature and Sources of Infrasound

Infrasound occurs both in nature (for example, during storms and earthquakes) and as a result of human activity (such as the operation of ventilation systems, large machinery, and wind turbines). For a long time, it was believed that if infrasound is not heard, it poses no health risk.

Previous Observations and Contradictions

There have been reports of people experiencing anxiety, fatigue, and irritation when exposed to areas with high levels of infrasound. However, scientific data on this topic has been inconsistent: some studies found no significant effects, while others noted discomfort and sleep disturbances.

Experimental Study

In the experiment, 36 volunteers were randomly assigned to four groups. Each group experienced different combinations of two factors: the presence or absence of infrasound and the type of musical accompaniment (calming or unsettling music). Infrasound was generated at a frequency of about 18 hertz and a volume of 75–78 decibels, similar to the noise level of industrial or ventilation equipment near residential areas. The music tracks were filtered to remove low frequencies to avoid distortion, and speakers were placed out of the participants’ line of sight. None of the participants were informed about the possible use of infrasound, but after the experiment, they were asked if they had noticed its presence.

Assessment of Condition and Results

After the experiment, participants evaluated their own state and the music they heard. Their saliva cortisol levels were also measured before and after exposure, providing an objective measure of stress.

Main Findings

Participants were unable to consciously determine whether infrasound was present, confirming that it cannot be consciously perceived. Nevertheless, music accompanied by infrasound was rated as sadder and provoked increased irritation and decreased interest in what was happening, regardless of the type of music. Infrasound gave any auditory stimulus a negative emotional tone.

Additionally, those exposed to infrasound showed a significant increase in cortisol levels compared to the control group. This indicates a direct physiological response to infrasound, rather than a subjective feeling of discomfort. While there were no clear signs of panic or intense fear, physiological indicators suggested that the environment was perceived as unpleasant and discomforting.