The Mysterious Hum Heard Around the World May Finally Have an Explanation
Researchers may have found an explanation for the phenomenon known as The Hum – a low-frequency sound perceived by only a small percentage of people. Scientists suggest that in most cases, it is not an external noise but rather low-frequency tinnitus.
Origin of the Phenomenon
The mysterious low-frequency hum, experienced by an estimated 2 to 4 percent of the global population, first gained widespread attention in the mid-1970s in Bristol, England. The Bristol Evening Post received numerous letters from residents reporting an unexplained sound. Although initial speculation pointed to industrial fans in a department store warehouse, the reports continued even after the warehouse closed. Similar accounts later emerged in other parts of the United Kingdom, as well as in the United States, Canada, Australia, and Europe. In 2012, the interactive World Hum Map and Database Project was created to collect reports from around the world.
Possible Causes: External or Internal?
Researchers have examined several hypotheses. One suggests that The Hum originates from external sources such as industry, infrastructure, or natural processes that emit low-frequency sounds. However, because these sound waves have long wavelengths, their source is extremely difficult to locate. Professor Markus Drexl of the Norwegian University of Science and Technology (NTNU) and his team studied 28 people in Germany who reported hearing an unexplained hum. Most participants did not have exceptional low-frequency hearing – only two showed slightly better-than-average ability in certain low frequencies.
Internal Noises of the Auditory System
The cochlea in the inner ear naturally produces faint sounds at various frequencies, known as otoacoustic emissions. Most people do not hear these sounds, but some individuals can perceive them. However, Drexl's study did not confirm this hypothesis – participants did not show such emissions in the low-frequency range. Therefore, scientists conclude that for most people, The Hum is a form of low-frequency tinnitus, a subjective perception of sound without an external source. Only a small number of individuals may have genuinely heightened sensitivity to low-frequency sounds.
Need for Further Research
Drexl notes that hearing research has primarily focused on higher frequencies. To properly assess the impact of low-frequency sounds and infrasound, a better understanding of how sensory systems process these frequencies is needed.
