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The Ear

Our world is full of sounds such as someone talking, music, a car engine, a cat purring, an aircraft flying overhead, a ball being hit and thousands more. The sound makes the air molecules vibrate and this vibration (actually a longitudinal wave) travels through the air until it reaches your ear.

The sound is "received" by your outer ear, rather like a dish aerial, and then travels along the outer ear canal until it reaches the eardrum. The eardrum is just what its name suggests a thin membrane like the skin of a drum. This vibrates when the sound waves hit it. Pressing on the other side of the eardrum are the middle ear bones.

These bones act like a series of levers, magnifying the movement produced by the eardrum until the final bone called the stirrup bone because of its shape, starts vibrating.

The stirrup bone transmits the vibrations to the inner ear a hollow organ filled with liquid and with the inside covered in fine hairs. The hairs are sensitive to movement and convert it to a series of electrical impulses. These signals are then carried by the nerve to the brain you can hear the sound.

The inner ear is also important in giving you a sense of balance. The movement of the fluid in the three semicircular canals tells you whether your head is upright or not and if not what position it is in.

The ear is a remarkable organ your ear can detect a range of loudness from the loudest to the softest sound of about a million million. This is about 1000 times greater than the range of intensity that your eyes can detect.

Your eardrum vibrates when the sound waves hit it but only very slightly. At the threshold of hearing for a sound of 3000 Hz it only vibrates about a hundred millionth of a millimetre and even for loud sounds it will only move a ten thousandth of a millimetre. Using a stethoscope or an old fashioned ear trumpet helps to collect and concentrate the vibrations and so makes it possible for you to hear fainter sounds than if you just used your ears with no extra help.

The human ear is also sensitive to a large range of frequency from about 20 Hz to 20 000 Hz a difference of 1000 times. As you get older the upper limit of hearing drops. You can notice a difference between the ages of 11 and 19 and adults cannot usually hear any sound above a frequency of 17 500 Hz.

People exposed to loud sounds for long periods (like pop groups or those working with very noisy machine tools) are likely to find that their hearing is getting worse more quickly. The ability of your ears to detect high frequencies (say around 4000 Hz) drops off much more than their ability to pick up low frequency sounds.


© Keith Gibbs 2020