Some people are bothered by low-frequency noise, such as that from ventilation systems, heat pumps, wind turbines, and electrical transformers, while others are unconcerned by it.
A new scientific study has revealed the reason behind this difference, as researchers found that the brain perceives these low-pitched sounds in a completely different way than normal sounds.
Sounds with a frequency below 16 Hz are known in scientific circles as "infrasound" (or infrasound waves), and it was long believed that they were inaudible to humans.
But researcher Carlos Jurado from the Norwegian University of Science and Technology asserts that this belief is inaccurate, noting that humans can indeed perceive these sounds if the sound level is high enough, but they perceive them more as a hum or bodily vibration than as a traditional sound, making them difficult to measure.
To understand this phenomenon, Jurado collaborated with researcher Torsten Marquardt from University College London, and they published their findings in the journal Scientific Reports. They concluded that the inner ear processes infrasound in a way that is completely different from how it processes ordinary sounds.
Within the inner ear are specialized sensory hair cells responsible for transmitting sound signals to the brain. However, at very low frequencies, the signals reaching these cells become extremely weak. This is where other supporting cells come into play. Previously known to regulate hearing sensitivity by receiving signals from the brain, these cells are now capable of generating electrical fields strong enough to send neural signals to the brain, thus enabling the perception of infrasound.
This may explain why low-frequency sounds seem different in nature from other sounds, since a small increase in sound pressure is enough to make them suddenly much louder, a phenomenon that can now be easily explained in light of these new findings.
An important application of this discovery is that it may help explain why some people are bothered by low-frequency noise while others do not, because the newly discovered mechanism may vary from person to person, opening the door to a better understanding of individual interaction with these sounds, and perhaps the development of engineering or health solutions to reduce their impact on the most sensitive groups.
