When I hear my mother’s voice, it sounds different from my father’s voice, and different from a bird or a drum. Why are the sounds we hear so varied, and how do they travel to our ears?
Sound is created when something moves rapidly, and creates a wave in the air around it. Our vocal cords do this, as does the skin on a drum, pushing the wave out into the world. This wave is made up of bands of air: more pressure, less pressure, high and low, back and forth as long as the sound lasts. Sound can only travel through something whose pressure can be changed, like air and water. So if you’re floating in space: perfect quiet.
But have you ever noticed how sound changes as it echoes around a gym? That’s because sound waves change when they bounce off things. A musical note will sound differently in a glass room than in one lined with velvet cushions. This affects musical instruments too! And the size of an instrument influences the sound it makes, from the deep growl of the tuba to the light chirp of a flute. Generally, bigger instruments make deeper sounds, with fewer waves per second.
And sound is not just high or low. Of course, it’s also soft or loud. But more interesting are differences that lead to a new tone or feel. For example, a violin and a flute might play the same note at the same volume, but they still won’t sound the same. Waves have amazing abilities to send subtle differences within a sound. And luckily for us, our ears use delicate hairs to detect these waves as they move through the air. Nerves connect the hairs to our brain, connecting us to the full orchestra of sound.