Researchers tested 28 people in Germany who reported an unexplained low-frequency hum, finding that most did not have unusually sensitive low-frequency hearing and measurable sounds produced within the ear did not explain most reports, so the team proposes low-frequency tinnitus for many participants. [1]

That is narrower than a solution to the Hum reported around the world, because although ScienceDaily's headline says the mystery may finally have an explanation, the page carries edited material from the Norwegian University of Science and Technology about one small diagnostic study that does not establish how common any cause is among all hearers. [1]

Only two participants showed better-than-average hearing at certain low frequencies, and even that test has limits because standard measurements may miss sensitivity within a very narrow band, such as a difference between 50 and 51 hertz, while tests for low-frequency otoacoustic emissions, faint sounds generated by the inner ear, also did not support that proposed explanation. [1]

Tinnitus remains a plausible account when someone perceives a sound that cannot be measured externally, yet real external sources also exist, as ventilation, heat pumps, traffic, wind turbines, ocean waves and wind can produce low-frequency sound that travels far and is hard to locate, and the researchers did not rule out such cases. [1]

Recruitment, controls, environmental monitoring, diagnostic criteria and treatment response remain open, so the 28-person result weakens two explanations within its sample and advances another without making every distant machine imaginary or every worldwide Hum report a symptom.

-- KENJI NAKAMURA, Tokyo