Glen MacPherson heard it when he was living on Canada's west coast. A low, persistent drone he couldn't locate or explain. When he moved to another city, it stopped. He became so preoccupied with understanding what he had heard that in 2012, he built an entire interactive database to collect reports from others around the world who had experienced the same thing.
He is not alone. For roughly 50 years, people around the world have reported an unexplained low-frequency hum, often heard indoors, difficult to detect outdoors, audible to some and completely inaudible to others. Now, a new study published in PLOS One tested 28 people in Germany who experience the sound and points to a surprising possibility that, for many, the source may not be outside at all.
“We believe people in this category have a form of low-frequency tinnitus,” study lead Markus Drexl, a professor at the Norwegian University of Science and Technology, said in a press release.
Read More: A Rare Hearing Disorder Can Make Sounds Loud and Uncomfortable
Tracking the Mysterious Hum
The Hum first surfaced in public consciousness in Bristol, England, in the mid-1970s, when a local newspaper began receiving letters from residents describing an unexplained droning sound. One theory suggested that industrial fans in a nearby warehouse were to blame. But when the warehouse closed, the sound stayed.
Explore All OptionsSince then, The Hum has been reported across the U.K., the U.S., Canada, Australia, New Zealand, South Africa, and several European cities. In the 1990s, it appeared in Taos, New Mexico, and Kokomo, Indiana, attracting significant media attention. Theories have ranged from industrial noise and ventilation systems to natural sources such as ocean waves, as well as more colorful explanations involving government agencies and extraterrestrials.
What made The Hum particularly strange was its selectivity. In the same room, one person could be driven to distraction by it while another heard nothing. Some found it merely irritating. Others reported it made them feel sick.
Testing Whether The Hum Comes From the Ear or the Outside World
Drexl’s team tested the most plausible scientific explanations. One was that people who hear The Hum may have unusually sharp hearing for low-frequency sounds that genuinely exist in the environment. Another was that the sound might come from the ear itself.
The inner ear is not just a passive receiver. The cochlea can produce faint sounds of its own, usually as a byproduct of the amplification process that enables hearing. Most people never notice them, but for some, these sounds can register as a persistent tone.
“Most of us don’t hear these sounds. However, a few people can actually hear the sounds that the ear itself produces. And these sounds can be measured objectively,” Drexl said.
Testing showed that two of the 28 participants had better-than-average hearing at certain low frequencies, meaning they may be picking up real environmental sounds that others simply cannot detect. But most participants did not show unusually sensitive low-frequency hearing. They also did not show measurable low-frequency sounds produced by the ear itself.
That left another possibility: the sound may be coming from inside the auditory system, even if it seems external. Drexl’s team suggests that, for many, The Hum may be a low-frequency form of tinnitus.
“Even though the group we tested was small, it still means that the hypothesis of having especially good hearing for low-frequency sounds does not hold for most people,” Drexl said in the press release.
The Hum Still Has Some Unanswered Questions
The study doesn’t close the book entirely. External sound sources haven’t been ruled out in every case, and Drexl points to a broader gap in scientific understanding.
“What we know about the hearing system is mainly based on how we capture and process sound with higher frequencies. We know less about how the auditory system handles and processes low-frequency sound, or infrasound,” Drexl explained.
For people who have spent years being told they were imagining things, the study offers some confirmation that the experience is real. For many, the source may simply be somewhere they weren’t looking.
Read More: How the Brain Processes Music for Those With Hearing Loss
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
- This article references information from a study published in PLOS One: On the potential sources of a low-frequency sound percept that only a few can perceive
