Researchers point to tinnitus in many reports of the global Hum
A small study found little evidence that most people who hear the Hum have unusually sharp low-frequency hearing or measurable ear-generated sounds.
By Tom Brennan · Health & Medicine Correspondent
3 min read
A long-reported low buzzing heard by some people around the world may often begin inside the auditory system rather than in the outside environment, according to researchers at the Norwegian University of Science and Technology. In a study of people who report hearing the sound, the team found limited support for two common explanations: unusual low-frequency hearing and measurable sounds produced by the ear itself.
The phenomenon, widely known as the Hum, has been described for decades as a low, persistent noise that some people hear while others nearby do not. NTNU said an estimated 2% to 4% of people worldwide report experiencing it, with some describing it as a nuisance and others as a sound linked to discomfort, illness or a bodily vibration.
According to NTNU, reports often involve indoor settings and nighttime conditions, when background noise is lower and people are trying to sleep. People who hear the Hum may look for engines, machinery or other nearby causes, only to find no clear source, the university said.
A phenomenon reported across countries
NTNU said the Hum drew broad public attention in Bristol, England, in the mid-1970s, when the Bristol Evening Post received letters from residents describing an unexplained noise. One proposed cause was industrial fans in a department store warehouse, but NTNU said complaints continued after the warehouse later closed.
Similar accounts later appeared in other parts of the United Kingdom, including coastal communities such as Hythe, Plymouth, Southampton and Swansea, as well as London, according to NTNU. The university said reports also emerged in the 1990s in Taos, New Mexico, and Kokomo, Indiana, and have since been documented in Canada, Australia, New Zealand, South Africa and European cities.
The Norwegian Broadcasting Corporation has reported unexplained humming complaints around Oslo in recent years, according to NTNU. The university also cited Canadian teacher Glen MacPherson, who created the World Hum Map and Database Project in 2012 after hearing the sound while living on Canada’s west coast.
Testing two leading ideas
Markus Drexl, a professor at NTNU, studied 28 people in Germany who said they heard an unexplained hum or buzz. The study, by Bonifaz Baumann, Andrej Voss, Carlos Jurado and Drexl, was published in PLOS One under the title “On the potential sources of a low-frequency sound percept that only a few can perceive.”
The researchers considered whether the sound could be a real low-frequency noise from industry, infrastructure or nature that only some people detect. NTNU said possible outside sources include ventilation systems, heat pumps, traffic, wind turbines, waves and wind.
The team also tested whether participants were especially sensitive to low-frequency sound. NTNU said most were not, though two showed better-than-average hearing at certain low frequencies.
Drexl told NTNU that the small sample still weakened the idea that exceptional low-frequency hearing explains most cases. He also noted a caveat: standard tests may miss very narrow hearing differences, such as sensitivity between closely spaced frequencies.
The researchers then examined whether the inner ear could be producing the perceived sound. NTNU said the cochlea can generate faint sounds known as oto-acoustic emissions, usually in the range of about 500 to 5,000 hertz, and those sounds can be measured with a microphone in the ear canal.
According to NTNU, the participants did not show low-frequency oto-acoustic emissions that would explain the Hum. Drexl’s team therefore pointed to low-frequency tinnitus as the most likely explanation for many cases, while saying physical external sources have not been ruled out in all reports.
Tinnitus is the perception of sound without an outside source, often first mistaken for a noise in the surrounding environment, according to NTNU. Drexl said more research is needed on how humans perceive low-frequency sound and infrasound, especially as concern grows about low-frequency noise from modern technologies.
This story draws on original reporting from ScienceDaily.