Sound — How Does a Voice Reach Our Ears?
We speak, a friend hears us, and we rarely stop to wonder what actually happened between the two.
Sound begins with a vibration. When we speak, our vocal cords vibrate and make the surrounding air vibrate. That vibration travels outward as a sound wave.
When the wave reaches another person's ear, it makes the eardrum vibrate. Tiny bones inside the ear pass the vibrations onwards, and eventually the inner ear converts them into electrical signals. The brain then interprets those signals as sound.
Sound therefore needs a medium—such as air, water or a solid—to travel through. That is why sound cannot travel through the vacuum of outer space.
Two properties we learnt in school help explain what we hear:
Frequency determines the pitch—whether a sound is high or low.
Amplitude is related to how loud the sound seems.
And there is a wonderful demonstration of how differently sound travels: place your ear against a railway track and a distant sound can sometimes be heard through the metal before it reaches you through the air.
So when someone speaks to us, what reaches our ears is not the person's voice itself travelling through space.
It is a pattern of vibrations travelling through a medium, which our remarkable ears and brain transform into something we experience as sound.
Another school lesson suddenly becomes rather magical.
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