Two loudspeakers ( L_1 and L_2 ) are placed with a separation of 10 m, as shown in figure. Both speakers are fed with an audio input signal of same…

Two loudspeakers ( $\displaystyle L_1$ and $\displaystyle L_2$ ) are placed with a separation of $\displaystyle 10$ m , as shown in figure. Both speakers are fed with an audio input signal of same frequency with constant volume. A voice recorder, initially at point $\displaystyle A$, at equidistance to both loud speakers, is moved by $\displaystyle 25$ m along the line $\displaystyle A B$ while monitoring the audio signal. The measured signal was found to undergo $\displaystyle 10$ cycles of minima and maxima during the movement. The frequency of the input signal is $\displaystyle \_\_\_\_$ Hz (Speed of sound in air is $\displaystyle 324 \mathrm{~m} / \mathrm{s}$ and $\displaystyle \sqrt{5}=2.23$ )