Two loudspeakers at an outdoor rock concert are located 3.5 meters apart. You ar

Question

Two loudspeakers at an outdoor rock concert are located 3.5 meters apart. You are standing 16.1 meters from one of the speakers and 20.8 from the other. During a sound check, the technician sends the exact same frequency to both speakers while you listen. The technician starts at 20Hz and slowly increases it to 30,000Hz.

1) What is the lowest frequency where you will hear a minimum signal ?

Hz

2) What is the second lowest frequency where you will hear a minimum signal ?

Hz

3) What is the lowest frequency where you will hear a maximum signal ?

Hz

4) What is the second lowest frequency where you will hear a maximum signal ?

Hz

Explanation / Answer

the path length difference, ( L = L1 - L2).

L/ = / 2

The problem says nothing about the initial phase difference, so I assume that the initial signals coming out of the loudspeakers are in phase. is the phase difference,
1 - Now what would be if it's maximum? And if it's minimum?
2 - Let's take the sound speed v=340m/s.
You have L . So from the above equation
f = v / = v /(2 L)
Subtitute for each case (max/min), you will get f.   

Reference https://www.physicsforums.com/threads/interference-frequency.411699/

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