Loudness and amplitude
The loudness of a sound tells us how strong or soft it is. Loudness depends on the amplitude of the sound wave. A large amplitude means the source is vibrating strongly and gives out more energy, so the sound is loud. A small amplitude means a weak vibration, so the sound is soft.
Key idea
Loudness is controlled by amplitude: larger amplitude → louder sound. Pitch is controlled by frequency: higher frequency → higher pitch.
Pitch and frequency
The pitch of a sound tells us how high or low it is. Pitch depends on the frequency of the vibration. A source that vibrates quickly has a high frequency and produces a high-pitched sound, like a whistle or a bird's chirp. A source that vibrates slowly has a low frequency and produces a low-pitched sound, like a big drum or a lorry engine.
| Change | Effect |
| Bigger amplitude | Louder sound |
| Smaller amplitude | Softer sound |
| Higher frequency | Higher pitch |
| Lower frequency | Lower pitch |
Example
On a guitar, a thin, tightly stretched string vibrates fast and gives a high pitch. A thick, loose string vibrates slowly and gives a low pitch. Plucking any string harder increases the amplitude and makes it louder, without changing the pitch.
Hearing range
A healthy young person can usually hear sounds with frequencies between about 20 Hz and 20 000 Hz. Sounds above this range are called ultrasound and cannot be heard by humans, although animals such as bats and dogs can hear them.
Remember
- Loudness ↔ amplitude.
- Pitch ↔ frequency.
- Human hearing: about 20 Hz to 20 000 Hz.