For more than half a century, people in different countries have reported hearing a low, mysterious sound similar to a “constant buzz or hum”, while those around them have been unable to hear it.
The phenomenon, known as the “global hum”, has remained one of the most puzzling scientific mysteries. A recent study suggests that the source of the sound may not be external, but could instead come from within the hearing system itself.
Researchers from the German Centre for Vertigo and Balance Disorders, in cooperation with the Norwegian University of Science and Technology, examined the phenomenon in a study published in the journal PLOS One.
The study concluded that many cases of the “global hum” may actually be an uncommon form of low-frequency tinnitus rather than a real sound coming from the surrounding environment.
A decades-old mystery
Tinnitus can cause people to hear different types of “phantom noises” in their ears, including buzzing, roaring, clicking, hissing and humming. It is a common condition affecting around 15 to 20 per cent of people and is more frequent among older adults, according to the Mayo Clinic.
The phenomenon gained attention in the 1970s after residents of Bristol, Britain, reported hearing a low-frequency sound of around 50 hertz.
Years later, similar reports emerged from Australia, New Zealand and several parts of North America. Those affected described the sound as a low buzz, roar or hum that continued for long periods, while people nearby could not hear it.
In many cases, the sound appeared in specific locations, such as bedrooms at night, and disappeared in other places, making it extremely difficult to identify its source.
What lies behind the phenomenon?
Instead of searching for the source of the sound in the surrounding environment, researchers studied the people who reported hearing it.
The study included 28 volunteers who reported experiencing the phenomenon. They underwent tests to examine two main possibilities.
The first possibility was that these individuals had unusually high sensitivity to low-frequency sounds.
The second suggested that they were hearing sounds produced inside their own ears, known as cochlear emissions. These are faint sounds naturally produced by the inner ear but usually not noticed by most people.
