Final answer:
When audio waves are 180° out of phase, they produce pure destructive interference, resulting in a wave with an amplitude of zero.
Step-by-step explanation:
When audio waves are 180° out of phase, they are said to be exactly aligned crest to trough, producing pure destructive interference. This means that the disturbances of the two waves are in opposite directions, causing them to completely cancel each other out and resulting in a resultant wave with an amplitude of zero.