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Wherever we are – no matter how tranquil it seems – we are constantly surrounded by sound.

Sound is simply vibrations in the air. When something makes a noise – like a ringing bell for example - it moves the air particles around it. Those air particles then move the air particles around them, carrying the pulse of the vibration through the air.

Ears are incredibly sensitive – and can hear even the faintest of sounds
Super Senses

Our ears are brilliant at detecting these vibrations. Sound waves enter the ear canal and make the ear drum vibrate. This moves the tiny chain of bones (ossicles) in the middle ear. The last bone in this chain ‘knocks’ on the membrane window of the cochlea and makes the fluid in the cochlea move. The fluid movement then triggers a nerve impulse to the brain.

Human ears are incredibly sensitive – and can hear even the faintest of sounds. They can detect pressure variations of less than one billionth of atmospheric pressure. The intensity or loudness of sound is measured in decibels.

Below are the rough sound levels of some everyday sounds you may encounter:

  • Human whisper 15 - 20 decibels (db)
  • Human speech 60-70 db
  • A lawnmower 90 dB
  • A car horn 110 dB
  • Jet plane take off 120 dB
  • A gunshot 140 dB

The distance you are from the sound source affects its intensity or loudness -- if you are far away, it sounds quieter. The levels above were recorded near the sound.

Our ears also hear a great range of pitches – or frequencies – of sound. This is measured in hertz. The human range is commonly given as 20 to 20,000 Hertz, though there is lots of variation between individuals, especially at high frequencies.

In the Sound episode, we journey through the spectrum from the very lowest frequencies below our hearing range to the very highest. Over millions of years animals have tapped into different properties of sound in extraordinary ways. Using giant speakers and cameras that can ‘see sound’, we enter a sensory world way beyond human hearing