Course:PHYS341/2018/Calendar/Lecture 27

Phys341 Lecture 27: Summary and web references

2018.03.16

Textbook Ch.18.1-18.6

Woodwind

1. Energy input: air reed, single/double reed
2. Closed and open pipes
   • An air-reed instrument like the flute - with all holes closed - behaves like a cylindrical pipe open at both ends.
   • It has a full range of harmonics – 1:2:3:4...
   • A single (or double) reed instrument like the clarinet - with all holes closed - behaves like a cylindrical pipe open at one end.
   • The fundamental frequency is an octave lower than that of a flute for the same length.
   • It has only odd-harmonics – 1:3:5:7...
   • The fundamental (1) is called the chalumeau register.
   • The next harmonic (3) is a called the clarion register (an octave and a fifth higher).
3. Bore shape
   • A non-uniform bore changes the position of pressure nodes.
   • Variation gives the instrument builder some leeway in correcting tuning problems caused by the tone holes.
   • Extreme case: conical bore.
   • Has same frequency spectrum as a cylindrical pipe open at both ends!
   • Saxophone, oboe show full 1:2:3:4... spectra.
4. Recorder
   • Air reed (textbook uses phrase “edge tone”).
   • Air jet deflected into or out of the instrument depending on resonance in tube.
   • (The resonating object controls the energy input – “feedback” - like the violin bow mechanism but not like a plucked string).
   • Cylindrical air column (approximately).
   • Tone holes
   • Distance between open holes define the playing length – approximately.
   • The bigger the hole, the better it defines the end of the column.
5. Cross-fingering
   • Because the small holes don’t completely “open” the tube, the pitch can be changed by closing holes downstream of the first open hole.
6. Textbook cases and reality
   • Bores are never perfectly cylindrical or conical.
   • Pressure nodes are never quite at the open end, nor exactly at an air reed opening.
   • Single/double reeds are never quite define a pressure antinode.
   • Open holes affect but don’t define the position of a pressure node.
   • Small holes don’t do much.
   • Big holes distort the spectrum.
   • Wind instrument design and manufacture is every bit as subtle and nuanced as lutherie.
7. Clutes and flarinets http://newt.phys.unsw.edu.au/jw/clarinetacoustics.html
8. Gershwin: Rhapsody in blue https://youtu.be/ss2GFGMu198