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How does amplitude affect the loudness of a sound?

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Watch a suspended vibrating spring to learn about the propagation of sound waves — sound Learn about the propagation of sound waves from a point source by observing the motion of a suspended vibrating spring.

In physics, the amplitude of a sound wave is defined as the magnitude of the fluctuation of pressure from its equilibrium position. This amplitude directly determines the sound's intensity, which the human ear perceives as loudness.12

When a sound source vibrates with greater force—such as plucking a guitar string harder—it causes a larger displacement of air particles. This increased displacement results in a higher amplitude, which translates to a more intense wave and a louder sound. Conversely, a smaller amplitude corresponds to a quieter sound.21

Acoustic intensity, which is the rate of energy transmission per unit area, is mathematically related to the square of the amplitude. While the human ear can detect a vast range of pressure variations, the amplitude remains the fundamental physical property governing how loud a sound is perceived to be.12