The “Hum” is a persistent, low-frequency buzzing or droning sound reported by an estimated 2 to 4 percent of the global population. While some observers attribute the noise to industrial machinery or environmental factors, researchers at the Norwegian University of Science and Technology (NTNU) suggest that for the majority of cases, the phenomenon may be a form of internal, subjective low-frequency tinnitus rather than an external acoustic disturbance.
Origins and Geographic Spread of The Hum
The phenomenon first entered the public consciousness in the mid-1970s in Bristol, England. According to reports from the Bristol Evening Post, residents complained of a constant, unexplained hum. While early theories blamed large industrial fans in a local warehouse, the reports persisted long after the facility closed. Similar accounts soon surfaced in other coastal UK communities, including Southampton, Plymouth, and Swansea.
The phenomenon eventually went global. In the 1990s, residents in Taos, New Mexico, and Kokomo, Indiana, began reporting identical experiences. Since then, the sound has been documented across Canada, Australia, New Zealand, South Africa, and various European cities. In 2012, Canadian teacher Glen MacPherson launched The World Hum Map and Database Project to aggregate reports, noting that the sound is most frequently observed in densely populated areas and is often more noticeable indoors at night.
Did you know?
The Hum is notoriously difficult to localize. Because low-frequency sound waves have long wavelengths, they can travel over significant distances, making it nearly impossible for residents to identify a specific source.
Testing the External Source Hypothesis
To determine if the noise is an external, measurable phenomenon, Markus Drexl, a professor at NTNU, led a study involving 28 participants in Germany who reported hearing the sound. The researchers aimed to identify if the hum originated from infrastructure, traffic, or natural environmental processes.
The investigation yielded two primary findings:
- No exceptional sensitivity: Most participants did not possess superior hearing capabilities in the low-frequency range. Only two individuals showed above-average sensitivity, effectively ruling out “super-hearing” as a general explanation.
- Lack of oto-acoustic emissions: The team tested whether participants were hearing sounds produced naturally by the cochlea. While the ear does generate faint, measurable sounds—known as oto-acoustic emissions—these were not present at the low frequencies reported by the study group.
The Link to Low-Frequency Tinnitus
Because external sources and physiological sound production were largely ruled out, researchers are focusing on subjective tinnitus. According to Professor Drexl, many individuals likely experience a form of low-frequency tinnitus where the auditory system perceives a sound that has no external source.
Tinnitus is typically associated with ringing in the ears, but it can manifest as a persistent hum or pulse. Unlike external noise, this perception remains constant even when a person changes locations. Drexl notes that while physical external sources—such as ventilation systems or heat pumps—cannot be ruled out in every instance, the scientific consensus is shifting toward internal auditory system malfunctions for the majority of persistent cases.
Future Research in Auditory Processing
The study of The Hum has highlighted a significant gap in scientific knowledge regarding how the human ear processes infrasound and low-frequency noise. Most existing audiology research focuses on higher frequencies, leaving the mechanisms of low-frequency sound perception poorly understood.
As technological noise pollution from road traffic and industrial fans increases, researchers are calling for more rigorous studies on how these frequencies impact the human auditory system. Understanding these processes is essential for distinguishing between environmental noise pollution and the subjective experience of tinnitus.
Frequently Asked Questions
Is The Hum a sign of a medical condition?
Researchers suggest that for many, it is a form of low-frequency tinnitus. It is not generally considered dangerous, but it can cause physical discomfort or sleep disruption.
Can the hum be recorded with a microphone?
In most documented cases, the sound cannot be captured by standard recording equipment, which supports the hypothesis that the sound is subjective rather than environmental.
Why do some people hear it while others in the same room do not?
If the cause is low-frequency tinnitus, the sound is perceived internally by the individual’s brain and auditory system, meaning other people present will not hear it.
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