Those with exceptional hearing have long been plagued, but so few people could hear the mysterious low rumbling sound that their complaints fell on deafer ears.

Now Tom Moir, a Scottish engineer and signals processing expert living in New Zealand, has succeeded in recording the hum — finally validating the complaints of many affected people from New Zealand to England and America, some of whom believed that they were losing their minds to the noise.

“People are deeply troubled by this sound,” said Dr Moir, of Massey University Institute of Information and Mathematical Sciences. “It is not just a little thing. It is really quite a major thing in their life,” he told The Times.

Using a high-sensitivity digital sound recorder and aided by a student who could hear the noise, Dr Moir visited about 30 homes in Auckland, the largest city in New Zealand, where the hum can be heard. Last week he succeeded in making a recording that he wants to share with people in other parts of the world — particularly in Bristol and in New Mexico, where the phenomenon is known to have occurred.

He has established that the sound is at a frequency of 56Hz. Although within the standard range of human hearing — which can range from 20 to 20,000Hz — it is too low for many people to detect. His testing of those able to hear the sound has revealed that their ability to detect low-frequency noise is about three times better than that of most people.

The sound, often described as being similar to the sound of air being blown over a bottle top, has troubled sensitive ears in Auckland’s northern suburbs and isolated parts of New Zealand’s far north for several years. One man who contacted Dr Moir became so frustrated by the sound that he deliberately damaged the hearing in one of his ears — by holding it close to a chainsaw engine — so that he could sleep.

Marie Peard, the Auckland designer, said that after having frequently left her home because of sleep deprivation, she now plays a CD of the sound of falling rain to mask the noise while she sleeps. “I tried Verdi, I tried Mozart but the hum would still wake me,” she said yesterday.

Unlike many others troubled by the sound who fear ridicule, Ms Peard is happy to be identified, saying: “For a long time I felt on my own and wondered whether I was going quite crazy because nobody else could hear it. I feel, by being identified, that at least I may be able to help others.”

Having succeeded in recording the sound, Dr Moir is anxious to know the cause but believes that an answer will be elusive. He is convinced that the sound is acoustic, not electromagnetic. The frequency is also too high for the sound to be produced by New Zealand’s 240-volt electricity home supply, which produces 50Hz.

Dr Moir emphasises that his expertise enabled him to find and record the sound; tracing the source will be a matter for other scientific disciplines. His research has shown that the sound is most often heard in homes located in a dip in the land or valleys which, he believes, might provide a shell-like effect that magnifies the sound.

In the mid-1960s the Bristol hum gained much attention. A group from London University studied the noise and recommended that those suffering from its effects wear a specially designed aluminium helmet.

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