A pair of in-phase stereo speakers is placed side by side, 0.85 m apart. You stand directly in front of one of the speakers, 1.1 m from the speaker. What is the lowest frequency that will produce constructive interference at your location?

Answer 1

For lowest-order constructive interference, the two distances from speaker to listener must differ by one wavelength.

Wavelength = sqrt[0.85^2 + 1.1^2] = 1.39 m

Frequency = (sound speed)/(wavelength) 340m/s/1.39m = 245 Hz