Loudness and amplitude

What does the loudness of sound depend on?

Sounds vary not only in terms of the pitch or frequency but also in their relative loudness.

Louder sounds are produced by larger vibrations of the source. Moving to-and-fro more makes a bigger disturbance and so a louder sound.

Just like pitch, the loudness heard depends on the person. A comfortable loudness for TV or music for someone might be painful for you. But not for everyone.

The amplitude of the vibration is measured in a way that everyone agrees on.

The human ear is sensitive to sounds over a huge range of loudness. The loudest sound that the ear can safely detect without suffering any physical damage is more that one billion times more intense than the threshold of hearing (where sounds can just be heard).

The ear reports huge increases in amplitude as small increases in loudness.