http://www.abc.net.au/news/ In 1985 a ringing sound was recorded in a boy’s ear, and it was not tinnitus. It’s actually the kind of sound a healthy inner ear makes all day every day. In fact your inner ear (or cochlea) is probably making its own sound right now. And your ‘ear song’ is as individual as your fingerprint. It’s called spontaneous otoacoustic emission (SOAE), and it’s a sign that your hearing is in the normal range. But almost 40 years after it was first discovered we still don’t know exactly what causes it. “It’s pretty uniformly agreed that the noise is caused by the hair cells on the cochlea vibrating, but no one knows exactly what makes them vibrate” says Dr Andrew Bell, who made the recording as part of his Masters research at the Australian National University. “It could be feedback between the rows of hair cells like ripples sloshing in a bathtub and resonating”. Unlike tinnitus, SOAE is usually so quiet you can’t hear it yourself at 10 to 20 decibels this sample was the loudest Bell ever recorded. “The sounds are usually fainter than this and often below the threshold of hearing (less than zero dB)”. “Each person has their own sound signature, with unique frequency and number of tones” says Bell. As well as being loud, the recording of the boy’s ear, is made up of about six pure tones between 1 and 3 kHz. “Most people have one to two tones”. It’s detectable in about 70-80 per cent of people, “but it really depends on how low you set the threshold (for the recording)” says Bell. And it’s more common in women’s ears and left ears. Bell’s research showed that a person’s signature tone was remarkably consistent over time, although it did vary a tiny bit with time of day and menstrual cycle. Bell has been tinkering away with the mysterious cause of the sound since his masters led to a PhD, and he’s shown no signs of giving up on it yet. “I don’t think it’ll be finally solved in my lifetime”.
ABC Science News, 25 June 2015 ;http://www.abc.net.au/news/ ;