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12-5 Sources of Sounds: Vibrating Strings and Air Columns

12-5 Sources of Sounds: Vibrating Strings and Air Columns. Notice that a chromatic scale …(p355) runs from a primary frequency, to the second harmonic, which is 2f 1 …this pattern continues for the next harmonic . We have discussed standing waves on a string… f=v/2L.

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12-5 Sources of Sounds: Vibrating Strings and Air Columns

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  1. 12-5 Sources of Sounds: Vibrating Strings and Air Columns Notice that a chromatic scale…(p355) runs from a primary frequency, to the second harmonic, which is 2f1 …this pattern continues for the next harmonic. We have discussed standing waves on a string… f=v/2L. …also v= …because tension and makeup of the string are important. See Example 12-6 and 12-7 Higher frequency standing waves are called overtones or harmonics.

  2. Tubes…open and one or both ends… • A tube open at both ends uses the same main equation as a standing wave in a string. • A tube closed at one end has the equation … • Fn = n=3,5,7… • See page 358 and 359 for diagrams and equations…

  3. 12-6 Quality of sound, and Noise • We have discussed loudness, and pitch, …but a 3rd characteristic of sound is quality, timbre or tone color. • The quality of sound depends on the number of overtones or harmonics. • Noise is sound pollution or additional sounds not desirable. • Noise can cause hearing loss…if it is in the range of 2000 Hz to 5000 Hz…this is critical because this is the range of music and speech. • A composite waveform is the composite of several harmonic waves…see pg 361.

  4. 12-7 Interference of Sound Waves: Beats • Much like interference in other waves can be constructive and destructive, when two sounds that are close, but different frequencies overlap there are bigger compressions and lesser rarefactions because the two waves cause interference. • This causes a perceivable ‘beat’ that can be heard and used. • Beat frequency equals the number of Hz difference between two waves or sources. • See page 363-364. See Example 12-12 p365

  5. 12-8 Doppler Effect • The Doppler effect is caused when either the source or the listener is moving which causes a change in the frequency. • There are equations to calculate the 4 situations… • If the source is moving toward the stationary observer 12-2a • If the source is moving away from the stationary observer…12-2b • If the observer is moving to the source…12-3a. • If the observer is moving away from the source…12-3b …See examples 12-13 and 12-14.

  6. HOMEWORK • Page 377 Pr# 26-32, 36, 41, 42-44,51-53 due Monday BOP. • Finish notes Monday • Lab Friday on Sound characteristics.

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