A new study published in PLOS One offers what researchers say is the most evidence-supported explanation yet for “The Hum” — an unexplained low-frequency droning reported by people around the world — pointing to subjective tinnitus in the low-frequency range as the likely culprit for most sufferers.
A research team led by Markus Drexl, a professor at the Norwegian University of Science and Technology (NTNU), has examined the auditory mechanisms behind a globally reported phenomenon in which a small subset of the population perceives a persistent, low-frequency buzzing or humming sound — one that no one else around them can hear, and no external source can explain.
The study, published in PLOS One in March 2026, enrolled 28 participants in Germany who reported hearing an unexplained humming sound and evaluated two primary hypotheses: that these individuals possess exceptional low-frequency hearing sensitivity, or that the perceived sound originates internally within the auditory system.
Testing Exceptional Hearing Sensitivity
The team began by assessing whether participants had unusually acute hearing for low frequencies that are objectively measurable. The vast majority did not. Only two participants demonstrated above-average hearing sensitivity at certain low-frequency ranges.
“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,” says Drexl.
He does note an important caveat: conventional hearing tests may not capture narrow-band microstructural differences in hearing thresholds — variations that could theoretically allow some individuals to perceive a very tight frequency range, such as between 50 and 51 Hz, with unusual sensitivity.
Ruling Out Otoacoustic Emissions
The researchers also evaluated whether participants might be perceiving spontaneous otoacoustic emissions — weak sounds the cochlea itself produces as a byproduct of physiological sound amplification, typically ranging from about 500 to 5,000 Hz. In rare cases, these emissions can be experienced as tinnitus and detected with a sensitive microphone placed in the ear canal.
“One hypothesis was that the participants in our group could hear oto-acoustic emissions at low frequencies. That’s why we tested whether they had them,” says Drexl. The answer was no.
Low-Frequency Tinnitus as the Leading Explanation
With the measurable-source hypotheses largely ruled out, the researchers concluded that the most plausible explanation for most Hum perceivers is subjective tinnitus — specifically, a phantom sound originating within the auditory system in the low-frequency range.
“Then there are people who hear something that cannot be measured objectively. We believe people in this category have a form of low-frequency tinnitus,” says Drexl.
This framing aligns with what is known about tinnitus more broadly: individuals initially attribute the sound to an external source, but as it persists across different environments, they eventually recognize it as internal. The key distinction with low-frequency tinnitus is that it mimics the character of environmental sounds — a hum from machinery, a distant engine, a subsonic vibration — making it more difficult to recognize as an auditory system phenomenon.
“Based on our results, although we haven’t ruled out cases of physical external sound sources, we suggest that subjective tinnitus in the low-frequency range is often the cause of hearing pulsations of low-frequency sound perceptions,” says Drexl.
A Gap in Audiology’s Understanding of Low-Frequency Processing
Drexl says the study underscores a broader gap in audiology research. The field’s understanding of how the auditory system captures and processes sound is heavily weighted toward higher-frequency ranges, leaving the low-frequency and infrasound domains comparatively understudied.
“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,” says Drexl.
That gap has practical implications. Over the past decade, growing concerns have emerged around noise exposure from technical sources operating in the low-frequency range (approximately 20–250 Hz) and infrasound range (below 20 Hz) — sources that include wind turbines, ventilation systems, and traffic infrastructure.
“If we want to conduct a thorough assessment of low-frequency sounds and infrasound, we first need a better understanding of how sensory systems process low-frequency sound and infrasound,” says Drexl.
Background on The Hum
The Hum phenomenon was widely discussed in Bristol, England in the mid-1970s, after residents began reporting an unexplained droning sound. Similar reports have since emerged in coastal UK cities including Hythe, Plymouth, Southampton, and Swansea, and later in Taos, New Mexico, and Kokomo, Indiana, in the US. The phenomenon has been documented in Canada, Australia, New Zealand, South Africa, and several European cities.
In 2012, Canadian Glen MacPherson launched the World Hum Map and Database Project, an interactive platform that aggregates data from people who experience the phenomenon worldwide.
The full study, “On the potential sources of a low-frequency sound percept that only a few can perceive,” is available in PLOS One at https://doi.org/10.1371/journal.pone.032681.
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