How loud?

The idea

Loudness is how humans perceive amplitude: larger amplitude sounds louder and loudness falls farther from the source; unlike intensity, which is measurable, loudness depends on the listener's hearing.

Near and far

A temple bell rings. You stand close to it, then far from it.

What do you think happens to the loudness as you move away?

• It decreases
• It increases
• It stays the same

Amplitude and distance

Change the size of the vibration (the amplitude) and the distance of the listener. The bar is a picture, not a measurement.

What we perceive

We perceive the amplitude of a sound wave as loudness. Larger amplitude sounds louder, smaller amplitude softer, and the loudness decreases as we move away from the source. Intensity can be measured. Loudness depends on how well the listener hears.

Loudness is how humans perceive amplitude: a larger amplitude sounds louder, and loudness decreases farther from the source. Intensity is measurable, but loudness depends on the listener's hearing ability.

Notes

Loudness is how we perceive amplitude. It falls with distance from the source. Intensity is measurable; loudness depends on the listener's hearing.

Check yourself

What do humans perceive as loudness?

Two sounds differ only in amplitude. How is the one with the larger amplitude heard?

What happens to the loudness as you move farther from the source?

Which of these can be measured, and which depends on the listener's hearing?

• The frequency of a sound wave. Humans perceive frequency as pitch. Loudness is how we perceive amplitude.
• The wavelength of a sound wave. Wavelength is a distance. Loudness is how we perceive amplitude.
• The amplitude of a sound wave — correct. Yes!
• Louder — correct. Yes!
• Softer. Sounds with larger amplitude are heard louder.
• With a higher pitch. A larger amplitude changes the loudness, not the pitch. Pitch comes from frequency.
• It increases. The loudness decreases as we move farther away from the source.
• It decreases — correct. Yes!
• It stays the same. The loudness decreases as we move farther away from the source.
• Loudness can be measured. Intensity depends on the listener. It is the other way round. Intensity is measurable, whereas loudness depends on the listener's hearing ability.
• Both depend on the listener. Intensity is a measurable quantity. Only loudness depends on the listener's hearing ability.
• Intensity can be measured. Loudness depends on the listener — correct. Yes!