A hidden sound with visible effects

Infrasound sits below the lower limit of typical human hearing, at frequencies under 20 hertz. People generally do not consciously hear it, yet it is common in everyday settings, from storms and traffic to ventilation systems and industrial machinery. New research highlighted by Frontiers in Behavioral Neuroscience suggests that this near-invisible part of the acoustic environment may still affect the body and mood.

The study points to a simple but unsettling idea: people may react to infrasound without recognizing what is causing the shift. That matters because unexplained feelings of unease, agitation, or discomfort are often interpreted through context. In a building already framed as eerie or haunted, for example, a real physiological response could be misread as something supernatural.

What researchers tested

The experiment involved 36 participants who sat alone in a room while listening to either calming or unsettling music. For half of them, hidden subwoofers also played infrasound at 18 hertz. Afterward, the participants reported their feelings, rated the emotional tone of the music, and said whether they believed infrasound had been present. Researchers also collected saliva samples before and after the session.

The design was meant to separate conscious perception from bodily response. If participants could identify the sound, then any mood effect might partly reflect expectation. If they could not, but their bodies still reacted, that would suggest the response was happening below conscious awareness.