Chapter 21 Musical Instruments

1. Lecture 22 Chapter 21Musical Instruments CR/NC Deadline Oct. 19

2. Musical Instruments Now that we understand some of the physics of sound, let’s analyze how musical sound is produced by different types of musical instruments. Physics 1 (Garcia) SJSU

3. String Instruments Standing wave on the vibrating string causes forced oscillation of the sounding board. • Frequency for a string depends on: • Length of string • Thickness and composition • Tension in the string Modern piano has many long, massive steel strings under high tension (hundreds of pounds) on a large sounding board. • Loudness depends on: • Amplitude of oscillation • Size of sounding board • Flexibility of sounding board

4. Standing Waves; Resonance Frequencies of standing waves on a particular string are called resonant frequencies. The lowest resonant frequency f1 is referred to as the fundamental and the higher resonant frequencies fn = nf1 as the nthharmonics.

5. Standing Waves of Guitar Strings Thin string In order for different strings to have different fundamental frequencies, they must differ in length and/or mass/unit length. A guitar has strings that are all the same length, but the mass/unit length varies. We change the effective length of a string by pressing it against the fingerboard. Thick string

6. Standing Waves - Piano In a piano, the strings vary in both length and density. This gives the sound box of a grand piano its characteristic shape. Once the length and material of the string is decided, individual strings may be tuned to the exact desired frequencies by changing the tension.

7. Musical Pipe Instruments Physics 1 (Garcia) SJSU

8. Standing Waves: Open/Open Pipe If the tube is open at both ends, both ends are antinodes, and the sequence of harmonics is the same as that on a string. All harmonics appear.

9. Demo: Whirly Tube Whirl a corrugated tube to produce a pure tone at the tube’s natural frequency. Bernoulli principle creates low pressure at the moving end, drawing air through the tube. L A

10. Playing Simple Horns Standing waves of different frequencies (different notes) are produced, depending on how musician blows into the horn. Simple bugle is just a long pipe wrapped in a coil so it’s compact.

11. Brass & Woodwind Vibrations Vibrations in a pipe instrument created by: • Vibrating one’s lips (e.g., trumpet) • Blowing past an opening (e.g., flute) • Blowing & vibrating a reed (e.g., clarinet)

12. Harmonic Series Music for natural horns and bugles is limited by harmonic series, the frequencies of the fundamental and overtones. Fundamental Physics 1 (Garcia) SJSU

13. Changing the Length To play notes beyond the harmonic series requires changing the frequency of the fundamental by changing the length of tube. Crooks Finger-holes Disadvantage: Reduced amplitude Disadvantage: Clumsy

14. Changing the Length Trombone uses a continuous slide to vary its length Cornett Physics 1 (Garcia) SJSU

15. Changing the Length Valves used in trumpet, tuba, and French horn Cornett Similar to using a crook but easy to open & close

16. Woodwind Instruments Resonant standing waves also produced in a pipe but the pipe length varied by air holes (finger-holes, keys, or pads). Flute Oboe Cor anglais Saxophone Clarinet Bassoon Meter stick Using air holes reduces amplitude of the sound

17. Percussion Instruments Create oscillations by striking an object, such as: • Stretched drumhead • Metal rod or disk • Wooden object

18. Drum Heads Drum heads are stretched membranes that vibrate at different frequencies depending on the membrane’s oscillation pattern. Note: These animations are not accurate because complex patterns should oscillate faster. Physics 1 (Garcia) SJSU

19. Key Points of Lecture 22 • Musical Instruments • Before Wednesday, read Hewitt Chap. 22 (first half). • Homework #16 due by 11:00 PM Friday Oct. 22.