What property affects the loudness of a sound?

The loudness of a sound is primarily influenced by its amplitude. Amplitude refers to the height of the sound wave; higher amplitude means more energy is carried by the wave, which translates to a louder sound for listeners. Essentially, when sound waves have a greater amplitude, they cause more significant pressure changes in the air, which our ears perceive as increased volume.

In contrast, frequency relates to the pitch of the sound, determining whether it is perceived as high or low. While speed and wavelength also describe properties of sound, they do not directly affect loudness. Speed is related to how fast sound travels through different mediums, while wavelength is the distance between consecutive peaks (or troughs) of the wave. Therefore, amplitude is the key determinant of how loud a sound is perceived.