The walls of a hall built for musical concert should

How do the frequency and amplitudes affect a musical sound?

Give one example each of natural vibration,forced vibration,and resonance.

State three conditions necessary for sound to be heard.

Define the following characteristics of sound:
$(a)$
$(i)$ Pitch
$(ii)$ Loudness
$(iii)$ Quality or Timbre
$(b)$ $A$ boy receives his echo $3 \, s$ later. Find the distance of the reflecting surface from the boy. Speed of sound in air is $342 \, m s^{-1}$.

Infrasound can be heard by