Interference

Professional Definition

Interference is the superposition of sound waves of the same frequencies.

The result of this process is the creation of a new wave with a changed amplitude. We distinguish two extreme cases: constructive interference (when the crests of the waves meet, summing their amplitudes and amplifying the sound) and destructive interference (when the crest of one wave hits the trough of another, leading to sound cancellation). In room acoustics, this phenomenon is closely related to the occurrence of the room's eigenmodes and comb filtering.

Acoustics in Simple Words

The best way to understand interference is by example of a swing. If you push the swing at exactly the same moment it is coming back (phase alignment), it swings harder – this is amplification. However, if you start pushing it in the opposite direction to its motion (opposite phase), you will slow it down – this is cancellation. In a room, waves reflected from the walls “collide” with waves coming from the speakers, creating loud (amplified) and dead (cancelled) zones in different places.

Summary

Interference is a physical phenomenon of the summation of sound waves, leading to local amplifications or cancellations of the signal. It is a key factor affecting the uniformity of sound reinforcement and frequency characteristics in listening rooms.