An increase in the range of molecular oscillations (Intensity) will be perceived as an increase in loudness.
Intensity and Loudness: If the energy producing a sound is increased, the frequency may stay the same, but the range of oscillations of the molecule will increase.
Hence, the molecules striking the ear drum will have more intensity and will be perceived as being a louder sound.
A curious feature of hearing is the range of degrees of loudness to which the ear can respond.