Loud, Soft, High, Low: The Science of Sound

Put your fingertips gently on your throat and hum. Can you feel something buzzing under your fingers? That buzz is called a vibration — a very fast back-and-forth movement. Every sound you have ever heard was made by something vibrating. Now try humming loudly, then very quietly. Try humming a high note, then a low note. Did the feeling in your throat change? In this lesson you will find out exactly why it changes.

All sounds are made by vibrations travelling through the air as sound waves. Sound waves are invisible ripples that move outward from the vibrating object and reach your ears. VOLUME Volume describes how loud or quiet a sound is. Volume depends on how much energy is in the vibration — in other words, how big the vibration is. A big vibration has large waves and produces a loud sound. A small vibration has tiny waves and produces a quiet sound. If you strum a guitar string very hard, it vibrates with a lot of energy and the sound is loud. If you pluck it gently, the vibration is smaller and the sound is quiet. PITCH Pitch describes how high or low a sound is. A bird tweet is high-pitched. A rumbling thunderclap is low-pitched. Pitch depends on how fast something vibrates — this speed is called frequency. A high frequency means the object vibrates very quickly, producing a high-pitched sound. A low frequency means it vibrates more slowly, producing a low-pitched sound. You can see pitch in action on a guitar. A thin, tight string vibrates quickly — high pitch. A thick, loose string vibrates slowly — low pitch. The string's thickness and tightness control how fast it moves, and that controls the pitch. Real-world example: Blow across the top of an empty bottle, then fill it halfway with water and blow again. The water makes the air column inside shorter. A shorter air column vibrates faster, so the pitch goes up. You have changed the pitch just by adding water!