BEAT FREQUENCYKathy Macarayan

WHAT IS A BEAT FREQUENCY IN SOUND?

“The sound of a beat frequency or beat wave is a fluctuating volume caused when you add two sound waves of slightly different frequencies together. If the frequencies of the sound waves are close enough together, you can hear a relatively slow variation in the volume of the sound. A good example of this can be heard using two tuning forks that are a few frequencies apart.”

Ron Kurtus, October 2013 (http://www.school-for-champions.com/science/sound_beat_frequencies.htm#.VQZWZUJupFI)

APPLICATIONS OF BEAT FREQUENCY

• The phenomenon of beats is most renowned for its influence in tuning instruments. When two frequencies are played simultaneously, instruments are tuned to match the correct frequency of the note; in other words, you are listening for beats. When beats can no longer be detected, the instrument is in tune.

BEAT FREQUENCY FORMULA

• Beat frequency can be solved by using the equation

• fbeat= | f1 -f2 |

• where f1 and f2 are the frequencies of the two sources

THE BEAT ENVELOPE “If you add two waves of slightly different frequencies, the resulting

amplitude will vary or oscillate at a rate that is the difference between the frequencies. That beat frequency will create a beat envelope around the original sine wave.”

Ron Kurtus, October 2013 (http://www.school-for-champions.com/science/sound_beat_frequencies.htm#.VQZWZUJupFI)

F1 (slightly slower frequency)

F2 (slightly faster frequency)

Because the frequencies are so close, you would hear a frequency that is the average of the two as well as the modulation of the amplitude as the beat frequency defined

by the previous formula.

EXAMPLE

A tuning fork with a frequency of 560 Hz is sounded together with a note played on a piano. Twelve beats are

heard in 4 seconds. What is the frequency or pitch of the piano note?

SOLUTION

• First, you must figure out how many beats are heard per second

• Beats per second = 12 beats/ 4 seconds = 3 Hz

SOLUTION

• Second, use the beat frequency formula to solve

• fbeat= | f1 -f2 |

• 3 Hz = |560 Hz- f2|

• There are two possible answers, f2= 557 Hz, 563 Hz

MORE HELP

• If you are still confused about beat frequency, check out this helpful youtube video by Brightstorm

• https://www.youtube.com/watch?v=ylBne5guWOc&spfreload=10

THANKS FOR WATCHING

• Images: http://www.taylorguitars.com/sites/default/files/hero-acoustic-guitars-browse-by-wood-taylor-guitars.jpg

http://avstrings.com/sites/default/files/imagecache/fullscreen/Metal%20Tuning%20Fork%20with%20Wood%20Block.jpg

http://www.uaudio.com/media/blog/2012/05/tune_hero.jpg