1. 1. Beats in Music Gillian Trotter Physics 101 203
2. 2. What is a beat? When two waves of similar amplitude, but different frequency interfere, there is a resulting wave. The resultant wave has a fluctuating amplitude, due to areas of constructive and destructive interference.
3. 3. What is a beat? By definition, a beat is a periodic variation of sound or amplitude due to the combination of two waves having similar but not identical frequencies.
4. 4. What do beats actually sound like? https://www.youtube.com/watch?v=V8W4Djz6jnY
5. 5. What do beats actually sound like? In the video on the previous slide, the pulsations that could be heard when both tuning forks were struck were the beats! The two waves were interfering and creating different resultant amplitudes.
6. 6. What do beats actually sound like? In the next video, we can see on a visual app how the resultant amplitude of two similar frequencies is the same. However, as the frequency of one of the sine generators is changed, a difference in amplitudes can be seen and heard. As the disparity between the two frequencies increases, the number of beat frequency also increases.
7. 7. What do beats actually sound like? https://www.youtube.com/watch?v=I9f6bP3x_yo
8. 8. Beat Frequency In the last video we heard that as the difference in angular frequency between the two waves increased, so did the beat frequency. Beat frequency is the number of pulsations heard in one second when two sound waves of different frequencies interfere.
9. 9. Beats in Music Beats are especially important in music. Different beat frequencies can be heard when instruments are being tuned, like at the beginning of an orchestral performance.
10. 10. Tuning The tuning of most stringed instruments is done using an electric tuner, but pianos used to be tuned with tuning forks. A key would be played, the hammer would strike the string, and a tuning fork would be struck at the same time. A note was in tune when the beat frequency was heard to be zero.
11. 11. Tuning Tuning a stringed instrument is usually done by increasing or decreasing the tension in the strings. When we think about this mathematically, this is because v = and v = (T/) Therefore = (T/) As tension is altered, so is frequency.
12. 12. A Question About Beat Frequency An A (440 Hz) is played on the piano at the same time as a tuning fork of 446 Hz is struck. 1. What is the beat frequency you hear? 2. How many beats will be heard in one second? 3. How many beats will be heard in 10 seconds?
13. 13. Answers 1. What is the beat frequency you hear? The beat frequency is equal to the difference between the two frequencies being played. To solve this question we simply have to subtract 440 Hz from 446 Hz, with the result being 6 Hz. 2. How many beats will be heard in one second? The number of beats heard in one second is equal to the beat frequency. This is because the measurement of Hz is actually equal to s-1. Therefore the answer is 6 beats per second, or 6 beats s-1. 3. How many beats will be heard in 10 seconds? Since we know how many beats are produced in one second, we can multiply 6 beats/second by 10 seconds to obtain 60 beats.