Hums - low frequency noises - cause much annoyance and may have other non-auditory effects on health. The issue is one of the most enigmatic factors in the assessment and control of environmental noise.

Over the past 20 years both scientific and lay publications have repeatedly drawn attention to mysterious hums, for which there often seems to be no explanation.1, 2 Universities, government departments, research establishments, and industrial and public companies have all been concerned,3, 4 as have learned societies, charities, and sufferers' associations. 5, 6 What are these hums, and why are there no clear explanations?

Audible sound is in the frequency range 20-20 000 Hz. “Infrasound” is inaudible sound in the frequency range 1-20 Hz - and if it is sufficiently intense it is sensed rather than heard. “Low frequency sound” is audible sound in the range 20-150 Hz. Hums seem to be perceived in the range 1-150 Hz, in which physical measurement is difficult.

Hums are …