When two sound waves of same amplitude are superposed, beats are produced.
Let the amplitude of each wave be:
\[
a.
\]
At maximum intensity, the two waves interfere constructively.
So, resultant amplitude becomes:
\[
A=a+a=2a.
\]
Now, intensity is proportional to the square of amplitude:
\[
I\propto A^2.
\]
Intensity due to one source is:
\[
I_1\propto a^2.
\]
Maximum intensity due to two sources is:
\[
I_{\max}\propto (2a)^2.
\]
\[
I_{\max}\propto 4a^2.
\]
Therefore:
\[
\frac{I_{\max}}{I_1}=\frac{4a^2}{a^2}.
\]
\[
\frac{I_{\max}}{I_1}=4.
\]
Hence, maximum intensity is four times that of one source.