Question

Why does the multiple reflection of sound amplify it?

Answer 1

Sound is a form of wave.
So a sound from a source contains a collection of waves.
Sound waves have a property called superposition.
Due to superposition when two sound waves meet together (constructive interference) their amplitude adds up and form a new wave with more amplitude.

​​​​​​So during multiple reflection, sound waves superimpose and produces a new wave with greater amplitude and this increase in amplitude makes it louder.

Eg:

Loudspeaker, Megaphone and bulb horn are devices used to send the sound in desired direction without spreading the sound all around. These devices act on the laws of reflection of sound wave.

In such devices, a funnel like cone shaped tube is used. Sound is introduced at the narrower end of tube and let to come out from wider end. Because of successive reflections, the amplitude of sound is added up which makes the sound louder. The name ‘Loudspeaker’ is given as it is used to make the sound louder.