HUMAN EAR MORE SENSITIVE THAN INITIALLY THOUGHT
Researchers have found that the human ear is more sensitive than it was thought to be earlier. There are many sounds – both natural and man-made – that are outside the dynamic range of the ear: which means that they’re either too quiet or too loud for us to hear. All these years, it has been ‘commonly accepted’ that the ‘too quiet’ sounds are innocuous and harmless, but a new study has confirmed that they’re not.
Humans can generally sense sounds at frequencies between 20 and 20,000 Hertz. Sounds under 250 Hz, though strictly present in the dynamic range, are difficult to make out, and most people don’t know when they’re exposed to sounds in this range. Therefore, their impact on how hearing changes as human beings age has been less than forthcoming.
Now, researchers at the Ludwig Maximilian University in Munich, Germany, have tested twenty-one volunteers with low-intensity sound such as a 30 Hz sound for 90 seconds. Then, they used probes to record the natural activity of the ear after the noise ended, by observing a phenomenon called spontaneous otoacoustic emissions (SOAEs), in which the ear itself emits fait whistling sounds.
SOAEs are generally stable over short time periods. But surprisingly, after being exposed to low-frequency sounds, participants’ SOAEs started oscillating, becoming alternately stronger and weaker. The fluctuations lasted about three minutes.
This is a groundbreaking discovery, because what this is means is that we’re liable to expose our ears unwittingly to low-level noise and permanent damage. So far, these low sounds were thought to be harmless. Whatever we cannot hear, we thought, cannot possible harm us.
Future research in this area will look at how wind turbine noise can affect the human ear.
