You are standing at the midpoint between two speakers, a distance D away from each. The speakers are playing the exact same sound of frequency 170 Hz in phase with each other. Describe what happens when you walk 1.5 m directly toward one of the speakers. Assume the speed of sound is 340 m/s. Also assume you can't hear any sounds except those produced by the speakers.
A. You begin by hearing a loud sound that gets quieter until you can't hear it anymore. Then it gets louder again until it is as loud as where you started. Then it gets quieter again until you can't hear it anymore.
B. You begin by hearing nothing, but the sound gets louder.
C. You begin by hearing nothing, but the sound gets louder. Then it gets quieter again until you can't hear it anymore.
D. You begin by hearing a loud sound that gets quieter until you can't hear it anymore.
E.You begin by hearing a loud sound that gets quieter until you can't hear it anymore. Then it gets louder again until it is as loud as where you started.
F. You begin by hearing nothing, but the sound gets louder. Then it gets quieter again until you can't hear it anymore. Then it gets louder again.

When the position of man is exactly at the meddle point between the speakers , sound waves from the speakers reaching man are in same phases ( path difference is zero. ) so intensity of sound is maximum .

Now , the man starts moving towards one of the speakers , his distance from one speaker becomes closer than the other creating path difference for the sound waves reaching his ears.

If he walks a distance of .5 m towards one speaker , path difference created

= .5 x 2 = 1 m

So , path difference = λ /2 ,

there will be destructive interference so minimum sound will be heard there.

When he walks a distance of 1 m , path difference created = 2m

path difference = λ

so there is constructive interference and maximum sound will be heard there.

Again we he walks a distance of 1.5 m , path difference created = 3 m

path difference = 3 λ /2

So there will be destructive interference so minimum sound will be heard there.

In this way we see that man starts from a point of maximum sound intensity , reaches a point of minimum sound intensity , then reaches a point of maximum sound intensity . At last he reaches a position of minimum sound intensity.