Dr. Jie Zou
• Noise corresponds to an irregular vibration of the eardrum produced by some irregular vibration.
• The sound of music has a different character, having periodic tones-or musical
“tones”.
• Musicians usually speak of musical tones in terms of three principal characteristics: pitch, loudness, and quality.
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Dr. Jie Zou
• The pitch of a sound relates to its frequency.
• Rapid vibrations of the sound source (high frequency) produce a high note, whereas slow vibrations
(low frequency) produce a low note.
• Different musical notes are obtained by changing the frequency of the vibrating sound source.
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• The intensity of sound depends on the amplitude of pressure variations within the sound wave.
– Sound intensity is a purely objective and physical attribute of a sound wave and can be measured by various acoustic instrument.
• Loudness is a physiological sensation.
The ear senses some frequencies much better than others.
– For example, a 3500-Hz sound and a 125-
Hz sound with the same intensity, the
3500-Hz sound sounds about twice as loud to most people as the 125-Hz soundhumans are more sensitive to the 3500-Hz range of frequencies.
Dr. Jie Zou PHY 1071 3

• Conventional musical instruments can be grouped into one of three classes:
– Those in which the sound is produced by vibrating strings
– Those in which the sound is produced by vibrating air columns
– Those in which the sound is produced by percussion-the
Dr. Jie Zou vibrating of a two-dimensional surface.
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• In a stringed instrument such as a violin, the vibration of the strings is transferred to a sounding board and then to the air.
Dr. Jie Zou PHY 1071 5

Dr. Jie Zou
• In a wind instrument, like a flute, the sound is produced by a vibrating air column in the instrument. The musician blows air against the edge of a hole to produce a fluttering stream that sets the air column into vibration.
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• In percussion instruments, such as a drum, a twodimensional membrane or elastic surface is struck to produce sound.
Dr. Jie Zou PHY 1071 7

• Chapter 21, P. 406-408, Exercises: 8, 26, 27,
30.
• The above problems are assigned from the
10 th edition of the textbook by Hewitt.
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