Understanding Beat Frequencies in Sound Waves

In summary, the conversation discusses the frequency of a resultant tone created by summing two tones of the same amplitude. It is explained that the resultant tone is the average of the two tones, and this can be seen mathematically by writing the sum as a product of trigonometric functions. The product has one frequency as the average and the other as a much lower frequency, resulting in the beat phenomenon.
  • #1
Sho Kano
372
3

Homework Statement


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Homework Equations


##f_beat=f_1-f_2##

The Attempt at a Solution


Why are the two different answers? Is it because the first question is asking for how often it fluctuates, and the other is actually asking for the frequency of the sound? Why is the resultant tone the average of the two?
 
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  • #2
Sho Kano said:
Is it because the first question is asking for how often it fluctuates, and the other is actually asking for the frequency of the sound?
Yes.
Sho Kano said:
Why is the resultant tone the average of the two?
Consider summing two tones of the same amplitude, A sin(ωt)+A sin(ψt). Do you know a way to write that as a product of trig functions?
 
  • #3
haruspex said:
Yes.

Consider summing two tones of the same amplitude, A sin(ωt)+A sin(ψt). Do you know a way to write that as a product of trig functions?
##2A[sin(\frac{wt+ \varphi t}{2})cos(\frac{wt-\varphi t}{2})]## There's an average in the sine, but not in the cosine, how does this relate to an average freq?
 
Last edited:
  • #4
Sho Kano said:
##2A[sin(\frac{wt+ \varphi t}{2})cos(\frac{wt-\varphi t}{2})]## There's an average in the sine, but not in the cosine, how does this relate to an average freq?
Assuming ψ and ω are similar in value, that product has one frequency as the average of those and the other factor a much lower frequency. Mathematically that does not make them fundamentally different, but to a human observer it will sound and look like a wave of the average frequency with an amplitude varying at the much lower (beat) frequency.
 

Related to Understanding Beat Frequencies in Sound Waves

1. What is beat frequency?

Beat frequency is the difference in frequency between two sound waves that are slightly different in frequency. This difference in frequency creates a pulsing or beating sound.

2. How is beat frequency calculated?

Beat frequency is calculated by subtracting the lower frequency from the higher frequency. For example, if one sound wave has a frequency of 400 Hz and another has a frequency of 405 Hz, the beat frequency would be 5 Hz.

3. What causes beat frequency?

Beat frequency is caused by the interference of two sound waves with slightly different frequencies. When these waves overlap, they create areas of constructive and destructive interference, resulting in the pulsing or beating sound.

4. How does beat frequency affect music?

Beat frequency can be used to tune musical instruments by adjusting the frequency of one note until it creates a beat with the other note. It can also create interesting effects in music when used intentionally, such as in the use of tremolo or vibrato.

5. Can beat frequency be harmful?

No, beat frequency is not harmful. It is a natural phenomenon that occurs in nature and is often used in music and sound engineering. However, prolonged exposure to loud sound waves, including those with beat frequency, can damage hearing. It is important to protect your ears from loud sounds and take breaks from exposure to loud noises.

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