@Abhisar
Two audio speakers produce, in step, the same sinusoidal sound of wavelength λ. A listening device is positioned at point Q in the room and registers no sound from the speakers. What characterizes the two sound waves as they arrive at point Q? Assume the room is anechoic (produces no echoes.)

One wave has twice the frequency of the other wave.
The two waves are a full cycle out of step.
One wave has twice the amplitude of the other wave.
The two waves are a half-cycle out of step.

Question

@Abhisar 
Two audio speakers produce, in step, the same sinusoidal sound of wavelength λ. A listening device is positioned at point Q in the room and registers no sound from the speakers. What characterizes the two sound waves as they arrive at point Q? Assume the room is anechoic (produces no echoes.) 
  
 One wave has twice the frequency of the other wave. 
 The two waves are a full cycle out of step. 
 One wave has twice the amplitude of the other wave. 
 The two waves are a half-cycle out of step.

anonymous · Answer

One wave has twice the amplitude of the other wave.