Question

Sound is said to be produce due to vibration of matters in a material .
but why is it so that harder the material stronger or larger is the sound .

Answer 1

Vibrating objects produce sound. The distance which a vibrating object moves is known as the amplitude of vibration. The larger the amplitude of vibration, the louder is the sound produced.
The number of vibrations per second is known as the frequency of vibration of an object. Increasing the frequency of vibration of an object increases the perceived pitch of the sound produced. Decreasing the frequency of vibration of an object decreases the perceived pitch of the sound produced.