Chapter 2: Q39E (page 540)
Two small stereo speakers are driven in step by the same variable-frequency oscillator. Their sound is picked up by a microphone. For what frequencies does their sound at the speakers produce (a) constructive interference and (b) destructive interference?
Short Answer
Any frequency which is an integer number of 819 will produce constructive interference.
The frequency that will produce the destructive interference is n409.5Hz.