Beats and Interference in Acoustics

• To understand the phenomena of interference and beats in acoustics

Wave interference is the phenomenon which occurs when two waves meet while travelling along the same medium. If we consider two waves of the same amplitude travelling in different directions, the individual waves are drawn in red and blue and the resulting displacement of the medium is drawn in green.

This type of interference is sometimes called constructive interference.

Destructive interference is a type of interference which occurs at any location along the medium where the two waves have a displacement in the opposite direction.

The result is that the two pulses completely destroy each other when they are completely overlapped.

The beat frequency refers to the rate at which the volume is heard to be oscillating from high to low volume, and it is obtained as the difference of the sources’ frequencies. So if two sound waves with frequencies of 256 Hz and 254 Hz are played simultaneously, a beat frequency of 2 Hz will be detected.

• Pair of La tuning forks with resonance boxes, hammer and clamps — 4317.40

• What do you think will happen if we repeat the same experience removing the clamp placed on one of the forks?
• A tuning fork with a frequency of 440 Hz is played simultaneously with a fork with a frequency of 437 Hz. How many beats will be heard over a period of 10 seconds?