## Destructive Interference

Two speakers, separated by a distance x = 4.24m are driven in phase by the same amplifier. A listener is located at point A, a distance L = 2.20 directly in front of one of the speakers. What is the lowest frequency for which there is a minimum signal at A due to destructive interference? The speed of sound can be taken as 343m/s

66.6 Hz .

66.6 Hz .

**Approach**

Destructive interference occurs when the crest of one wave lines up with the trough of the second wave. Since the waves coming out of the speakers are in phase, this implies that for destructive interference to occur at the listener, the path difference of the two waves must be equal to odd half-integer (n = 1/2, 3/2, 5/2, ..) number of wavelengths. For lowest frequency, n = 1/2.

## **Solution**

Given quantities:

- L = 2.20 m
- x = 4.24 m