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Pitch and Range in Wind Instruments - Learning Object 6

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Pitch and Range in Wind Instruments - Learning Object 6

An explanation of how wind instruments produce music, and what determines the range of notes that a wind instrument can play.

An explanation of how wind instruments produce music, and what determines the range of notes that a wind instrument can play.

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Pitch and Range in Wind Instruments - Learning Object 6

1. 1. PITCH AND RANGE IN WIND INSTRUMENTS By Yong Jia Bu Physics 101 203
2. 2. • music produced on wind instruments come from the vibrations of air through the instrument • we can approximate most wind instruments as cylindrical tubes through which air is blown area of high pressure area of low pressure • this may look very much like normal sound waves in air, but because they are confined to the cylindrical tube (or air column), vibrations of air inside the instrument actually become standing waves • To understand these standing waves, we need to first look at how air at the ends of the air column interact with atmosphere
3. 3. Flute: open-open tube Clarinet: closed-open tube It is probably easy to understand that the clarinet is closed at one end (mouthpiece completely covered by player’s lips when playing), but it may not seem obvious that the flute is an open-open tube. When playing, a flautist does not cover the hole in the mouthpiece entirely, but blows air across the mouthpiece. Air can still come in contact with atmospheric air this way. • most wind instruments are of either the open-open tube or the open- closed tube type • open ends are parts of the tube where air inside the tube makes contact with the outside, atmospheric air
4. 4. • It is relatively easy for a player to change the air pressure inside the wind instrument by blowing air into it • it is NOT easy to change atmospheric pressure outside the instrument • as vibrations in the instrument reaches the inside air and atmospheric air interface, it is almost as though the vibrations “hit a wall” and then sends sound waves in all directions • the waves that are reflected back into the instrument after bouncing off the atmospheric “wall” now travel through the instrument in the opposite direction To audience
5. 5. • standing waves are formed when two waves of the same amplitude, wavelength, and frequency travel in opposite directions and interfere with each other Fixed end Fixed end node Anti-node Anti-node • standing waves only form if they can vibrate along a length of medium that is some integer multiple of ½ of the wavelength; otherwise, when the wave is reflected, the amplitude doesn’t quite add up to something that stays constant! • the pitches (frequencies) that wind instruments can produce depend on the length of the instrument
6. 6. Fixed end Fixed end • The fundamental frequency of a note produces a standing wave like the one below: • the fundamental frequency has no nodes between the fixed ends, and it isn’t possible to fit any longer wavelengths into the medium without disrupting the standing wave • Think of how instruments with lower ranges are larger, longer, so that they may play notes with longer wavelengths Bassoon Range: A1–E5 Flute Range: C4–C7
7. 7. Open (hits atmosphere) Open (hits atmosphere) • Open-open tube, e.g. flute: both ends open to the atmosphere, a wave is sent out every time the vibrations reach either end Open (hits atmosphere) Closed (no vibrations sent out) • Closed-open tube, e.g. clarinet: one end is a closed, dead end with zero air movement (air pressure is always at a maximum at this end because air has nowhere to expand) Longest possible wavelength λ = 2*length of tube Fundamental frequency f = v/2*length of tube Longest possible wavelength λ = 4*length of tube Fundamental frequency f = v/4*length of tube This shows why the clarinet can play in a lower range than the flute although the two are about the same length.
8. 8. • A note that is an octave above another note has exactly double the frequency of the other note C5: f = 523.23 Hz C4: f = 261.63 Hz • The piccolo is designed to be an instrument that plays everything at one octave higher than a regular flute. If we measure the distance from the piccolo’s mouthpiece to its bell, we can see that this distance is about ½ of the distance on flute (ignoring end corrections). The piccolo’s fundamental frequency is therefore an octave higher. Piccolo Flute
9. 9. 1. Suppose you accidentally dropped your flute during practice and one of the keys has gotten twisted so it no longer closes completely. What would this mean in terms of the range of notes you can/can no longer play (assume the flute is a simple open-open air column and ignore modern designs on the instrument that change its properties)? 2. Because your flute is broken you are practicing your clarinet instead. But there seems to be a leak on your clarinet as well. You identify that the leaky key is 2/3 down the length of your clarinet (measured from the mouthpiece). Assuming that your clarinet is a simple closed-open air column of length L, calculate the difference in frequencies between the original lowest note that you could play and the lowest note that you are able to play while there is a leak (the answer is in terms of L).
10. 10. 1. If the flute is a simple open-open air column, then its length is effectively only as long as its last closed key. Theoretically, if there is a key in the middle that refuses to close, air can contact the atmosphere at this leaky point, making it the new “fixed end” of the air column and rendering all keys past it useless. And so notes with wavelengths greater than two times the length of the mouthpiece to the leaky key are no longer playable. The closer the leaky key is to the mouthpiece, the fewer notes will be left playable. 2. A closed-open tube has the fundamental frequency f = vair/4L, so the normal fundamental frequency should be about 86L Hz. The new fundamental frequency is f = vair/(4*(2/3)L), which is 129L Hz. The difference between the original frequency and the new frequency is 43L Hz.
11. 11. Wolfe, Joe. Poetics. “Open vs. Closed Pipes (Flutes vs. Clarinets).” The University of New South Wales School of Physics. The University of New South Wales, n.d. Web. 7 Mar. 2015. <http://newt.phys.unsw.edu.au/jw/ flutes.v.clarinets.html>.