# PHYS 2211 Module 15.4

## Interference of Sound Waves

15.4 Interference of Sound Waves

### Learning Objectives

By the end of this section, you will be able to:

• Explain the mechanism behind sound-reducing headphones

### Interference of Sound Waves

Discuss!

Two loudspeakers, A and B, are driven by the same amplifier and emit sinusoidal waves in phase. Speaker B is 2.00 m to the right of speaker A. Consider point Q along the extension of the line connecting the speakers, 1.00 m to the right of speaker B. Both speakers emit sound waves that travel directly from the speaker to point Q. What is the lowest frequency for which

(a) constructive interference occurs at point Q;

(b) destructive interference occurs at point Q?

Suppose that speaker A emits a sinusoidal sound wave of frequency 500 Hz and speaker B emits a sinusoidal sound wave of frequency 1000 Hz. What sort of interference will there be between these two waves?

Two small stereo speakers (black dots) are driven in step by the same variable-frequency oscillator. Their sound is picked up by a microphone arranged as shown. For what frequencies does their sound at the microphone produce (a) constructive interference and (b) destructive interference?