Download
physics 1251 the science and technology of musical sound n.
Skip this Video
Loading SlideShow in 5 Seconds..
Physics 1251 The Science and Technology of Musical Sound PowerPoint Presentation
Download Presentation
Physics 1251 The Science and Technology of Musical Sound

Physics 1251 The Science and Technology of Musical Sound

121 Views Download Presentation
Download Presentation

Physics 1251 The Science and Technology of Musical Sound

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

  1. Physics 1251The Science and Technology of Musical Sound Unit 3 Session 28 MWF Clarinets and Other Reeds

  2. Physics 1251 Unit 3 Session 28 Clarinets et cetera What pitch (frequency) does a flute play if the length from the embouchure to the finger hole is 67.5 cm [∼26½ inches] (including end corrections) when the temperature in the tube is 37 C? f = v/2L′; v =343 + 0.6 (T-20C) v = 343 +0.6(37-20) = 343 + 0.6 (17) = 353 m/s f = 353/(2 ‧ 0.675) = 262 Hz. With no warm up: f ′ = 344/354 f = 255. Hz, Δf = f ′– f = 262 –255 = 7 Hz. ₧ = 3986 Log (255/262) = - 47¢, ∼1/4 tone ♭

  3. Physics 1251 Unit 3 Session 28 Clarinets et cetera With what velocity should the flautist blow to produce a stable tone of 262 Hz if the embouchure is about 0.01 m? f = 0.2 vjet / b 262 Hz = 0.2 vjet /0.01 vjet = 262 ‧ 0.01/0.2=13.1 m/s (≈ 30 mph)

  4. Physics 1251 Unit 3 Session 28 Clarinets et cetera 1′ Lecture: • Reed instruments are stopped pipes. • The clarinet has a cylindrical bore and is a stopped pipe; consequently, only odd harmonics are significant. • Conical pipes exhibit all harmonics, even in stopped pipes. • The saxophone, oboe and bassoon‒all have conical bores.

  5. Physics 1251 Unit 3 Session 28 Clarinets et cetera Comparison of Flute and Clarinet Registers • Overblown flutes jump from a fundamental f1= v/2L to an octave f2 = 2f1 in the second register; an octave (2x) and a perfect fifth (3/2) f3 = 3 f1 =3 (v/2L) in the third register. • Overblown clarinets jump from a fundamental f1 = v/4L to an octave (2x) and a fifth (3/2)‒“the twelfth‒” in the second register, because only odd harmonics produce standing waves in a stopped cylindrical pipe.

  6. f1 f2 f3 f4 ♩ ♪ ♫ fn ~ ~ Physics 1251 Unit 3 Session 28 Clarinets et cetera Reed Instruments • The reed produces a pulsation in the pressure admitted to the pipe; the pressure standing wave feeds back to control the oscillations of the reed. Standing wave frequencies Reed pulsations Feedback

  7. Physics 1251 Unit 3 Session 28 Clarinets et cetera The Clarinet: Bell Body Reed The clarinet has a cylindrical bore.

  8. Air flow Tonguing Physics 1251 Unit 3 Session 28 Clarinets et cetera The Single Reed 80/20The reed opens and closes like a valve, pressurizing the pipe when open, closing due to the Bernoulli effect when the air flows. Reed

  9. Physics 1251 Unit 3 Session 28 Clarinets et cetera Hard and Soft Reeds 80/20A hard reed is one for which the frequency is determined by its stiffness and dimensions. A soft reed flexes easily and vibrates at the frequency of external pressure fluctuations. Soft Reeds Hard Reed: Harmonica Clarinet Oboe

  10. Physics 1251 Unit 3 Session 28 Clarinets et cetera Harmonium or Reed Organ Hard or soft reed?

  11. Air flow Physics 1251 Unit 3 Session 28 Clarinets et cetera The Double Reed 80/20The reed opens and closes like a valve, pressurizing the pipe when open, closing due to the Bernoulli effect when the air flows. Pressure Pulses Reed Tip

  12. Physics 1251 Unit 3 Session 28 Clarinets et cetera Bassoon Reeds Double Reed The Bassoon uses a double reed, as does the Oboe and English Horn. Reed Double Reed

  13. Physics 1251 Unit 3 Session 27 Flutes et cetera Bernoulli Effect • 80/20The pressure in a fluid decreases as the velocity increases. • Thus, as the air flows past the reed, it is forced closed. Bernoulli Effect

  14. Pressure inverts Physics 1251 Unit 3 Session 28 Clarinets et cetera 80/20Feedback from the pressure standing wave locks the frequency of the oscillation of the reed. f2n-1 = (2n-1) v/ 4L′ Pressure wave L′ = L + 0.3 d 0.3 d

  15. Physics 1251 Unit 3 Session 28 Clarinets et cetera Other Bore Shapes: Conical‒ Pressure node Pressure anti-node Pressure anti-node

  16. Physics 1251 Unit 3 Session 28 Clarinets et cetera 80/20For a stopped conical pipe: fn≈ nv / 2(L′ + c) if c << λ L′ = L + 0.3 d L′ d c 0.3 d

  17. Physics 1251 Unit 3 Session 28 Clarinets et cetera Why? Z changes along the length of the pipe. Weighted String Analogy

  18. Physics 1251 Unit 3 Session 28 Clarinets et cetera Saxophone: Conical bore English horn: Other Reed Woodwinds: Conical bore Oboe: Conical bore Bassoon: Conical bore

  19. Physics 1251 Unit 3 Session 28 Clarinets et cetera The Reed Pipes of Organs: • Conical • Voiced by Reeds • Tuned by Spring Pipe Shallot Reed Tuning Spring

  20. Physics 1251 Unit 3 Session 28 Clarinets et cetera Reed Pipes

  21. Reed Physics 1251 Unit 3 Session 28 Clarinets et cetera Bicycle Horn

  22. Physics 1251 Unit 3 Session 28 Clarinets et cetera Edge versus Reed Cylinder versus Cone

  23. Physics 1251 Unit 3 Session 28 Clarinets et cetera Summary: • Reed Instruments are stopped pipes. • L′ = L + 0.3 d • f2n-1 = (2n-1) v/4L′ for stopped cylindrical pipes such as the clarinet. • fn = n v/ 2(L′+c) for stopped conical pipes such as the saxophone, oboe, bassoon, etc. • Soft reeds act as pressure valves that respond to the frequency fed back from the standing waves of the pipe.