Imagine you are in an open field where two loudspeakers are set up and connected to the same amplifier so that they emit sound waves in phase at 688 Hz. Take the speed of sound in air to be 344 m/s.
(A) If you are 3.00 m from speaker A directly to your right and 3.50 m from speaker B directly to your left, will the sound that you hear be louder than the sound you would hear if only one speaker were in use?

Explanation:

frequency of sound waves = 688 Hz

wavelength = 344 / 688 = .5 m

The problem is based on interference of sound waves

For the observer , path difference of sound waves reaching his ear

= 3.5 - 3.00

.5 m

= wavelength

Path difference is equal to wavelength so there will be constructive interference and hence louder sound will be heard by the listener than normal sound as sound waves interfere constructively.