Standing Sound Waves

Sound levels are loudest at positions where standing sound waves exist between the speaker and the reflecting barrier.

Discussion

As the speaker is moved toward and away from the reflecting surface, it passes through several positions at which standing waves can be established. At these positions, sound levels are greatest, because energy from the speakers is most efficiently absorbed by the sound wave, resulting in increased wave amplitudes and corresponding loudness. This demonstration is a three-dimensional version of interference of waves from two point sources.