University of Auckland/Department of Physics/Physics 102/Beats

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'Beating' is a phenomena where sound waves of different frequencies interfere with each other, and to the human ear they create a rhythmic beating noise. This is a result of the alternating constructive and destructive interference caused by the two sound waves being at different frequencies.

Wave diagram for a Beat Frequency, and a diagram of the two individual sound waves that it comprises of

Unlike a normal interference pattern the resulting wave is not a standing wave, which means the nodes and anti-nodes are not in fixed positions. As a result of this the nodes and anti-nodes periodically reach our ears, which causes the rhythmic beating pattern; when we hear the anti-node we hear a beat and then the relative quiet of the node follows, followed again by a beat caused by an anti-node.

When we have two waves that interfere but with different frequencies.

E.g. strumming 2 or more strings of gutitar simultaneously or hitting 2 or more keys on a piano until the waves reasonate or else form a harmonic; (harmonising, Laman description) tune.

Beat Frequency Calculations

The beat frequency is defined as

fbeat = | f1 - f2 |

Beat Period

The period of a beat is related to the beat frequency by: Tbeat=1/fbeat

Practical Example

Beats can be further understood by two people walking in different strides (one taller and one shorter person). At some point in time their individual step will be in time with the others step and out of step.

Adding waves with different frequencies

External Resources

Beats simulation (*Beware*)

Beats simulation (Java Applet)


Heres a link thats like an online interactive textbook. Will answer any questions you might have..: (dhic014)

This link is an interactive way of learning, but isnt very unique. THere are other external links that i find are more useful for learning. klit014

Fun and interactive resource, good for experimenting different theories. crav005

I found this page to be similar to other external links, but with less information. Not as informative and somewhat unclear. vaio002

Personally I find this whole wiki idea to be kind of annoying and unhelpful to my learning, does not motivate me to learn whatsoever.

this page is helpful as it helped me in my assignment and understanding more abouts beats.(kpat122)