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Chapter 21 Musical Sound• 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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Pitch

• 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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Sound intensity and loudness• 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 sound-humans are more sensitive to the 3500-Hz range of frequencies.

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Musical instrument

• 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 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.

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• 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 two-dimensional membrane or elastic surface is struck to produce sound.

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Homework

• Chapter 21, P. 406-408, Exercises: 8, 26, 27, 30.

• The above problems are assigned from the 10th edition of the textbook by Hewitt.