$S_1$  and  $S_2$  are two identical sound sources of frequency 656 Hz. The source  $S_1$  is located at O and $S_2$  moves anti-clockwise with a uniform speed  $8\sqrt{2}m{s}^{-1}$ on a circular path around O, as shown in the figure. There are three points P, Q and R on this path such that P and R are diametrically opposite while Q is equidistant from them. A sound detector is placed at point P. The source  $S_1$  can move along direction OP. [Given: The speed of sound in air is  $324m{s}^{-1}$]