Flute Physics PowerPoint Presentation

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1 Flute Physics

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2 Normal modes of a column No motions, large pressure variations No pressure variation, large motions

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3 Is the flute -an open column -a closed column or -one end open and other end closed? How can we find out?

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4 Experiments on the open pipe Blocking the end Half blocking the end How are high notes made easier to play? Harmonics of Flute Frequency f is speed of sound c divided by wavelength λ Fingering and pitch change. Effectively shortening the pipe. Comparing the flute and the recorder lengths

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5 Oscillating Air Stream

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6 Pitch What changes the pitch? -Speed? -Distance from mouth to edge? -Covering of hole?

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7 Blowing Breathy sound: How do you get rid of it? High notes vs low notes: What does the flutist do to change octave? (whirly tube?) Vibrato: How does it change the sound? (dynamics, timbre, pitch) How does the flutist do it?

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8 Thumb hole Favors the higher overtones allowing the flutist to play an octave higher without over-blowing. However the thumb hole is not in the correct place for every note in the octave.  fingering changes from octave to octave

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9 Dynamics As the vibration becomes larger, more harmonics appear. Loudness in most instruments is accompanied by a change in strength of overtones. The flute does not have a big dynamic range. Why? How do flutists compensate?

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Perceptual fusion and voicing Voices stand out if their overtones move together. If overtones don’t move in pitch then the sound does not sound like a voice. Tones with no variation in pitch sound dull. Demo from Perry Cook’s book. A bell has many overtones. 3 groups of overtones are given different vibratos. As the vibrato grows three voices are heard separately. 10

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11 Adjusting pitch The distance between the mouth and edge is fixed for a recorder. When you blow harder the note is sharper. Flutists can compensate by turning the flute. Some recorder players compensate with different fingerings for louder notes! If you add vibrato exact pitch is less precise (add vibrato to allow louder notes to still be effectively in pitch)– vocalists do this too

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12 Material of Flute Does it matter? Wood vs metal. Silver vs. steel. How about with recorders? What part of the instrument mostly affects the tone? Timbre, temperature and humidity. Experiments with Heads Record wooden flutes vs metal flutes

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13 Wood vs metal flutes wood flute – metal flute –

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14 The modern flute (Boehm) Larger holes and covering system Key rings and coupling of keys Cylindrical body and tapered head How do these characteristics improve or change the sounds of the flute? F# experiment, low high notes flute+recorder Moving crown while playing low notes and then high notes

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15 Recorders and tapered barrel Taper improves higher octave tuning at the expense of some tonality and loudness Experiment: octaves with penny whistles and recorder

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16 End correction Effective length of pipe is L+Δ Δ~0.61a where a is the diameter of the pipe For a flanged pipe Δ~0.85a As the end correction depends on wavelength, a flute is not in pitch across octaves. This leads to the design of tapered ends.

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17 End correction Width of the barrel does make a difference. Experiment: diameter barrel End of flute does change the pitch (see Chinese flute). Placement of rice paper near mouth so all notes have extra vibration Dizi

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18 Chinese flute Rice paper has its own vibrating frequencies and also adds noise

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19 Design of Mouthpiece depth of mouthpiece determines pitch range for a single note

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What sets diameter of bore? Short fat bores are poorer in high overtones. If the bore is too thin, the low overtones are difficult to excite (e.g. thin whirly tube). This would suggest that one uses the same ratio of bore diameter to length for all instruments. However for low notes the sound is dull unless the high overtones are strong. In organs the lower pipes tend to be narrower. (2/3 diameter increase for a pipe twice as long). 21

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Narrow vs Wide Flutes Narrow flutes are better for high registers Wider flutes louder and have richer timbre e.g. Indian flutes vs penny whistle, piccolo, Japanese flute 22

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Wide holes vs narrow holes recorder vs bamboo flutes 23

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Hole size and Flared ends Louder sound if holes are larger The sound that escapes through a hole depends on the wavelength. If the wavelength is much larger than the hole then not much sound radiates. Low instruments tend to have bells at the end Instruments with finger holes (meaning not brass) tend to lack bells. Bells on instruments with holes (clarinets, oboes) tend to primarily affect notes played with nearly all holes closed. Exceptions: bassoon (bass but no bell), sax (large holes and large bell), trumpet (has bell but is soprano) 24

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Flared ends and buildup of sound The shape of the end sets boundary condition as a function of frequency. If radiation is too efficient then sound won’t build up inside instrument. Trade off between build up and radiation. 26

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27 Calculating pitch In practice it is difficult to calculate the pitches played by a flute as a function of positions and size of holes

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Trends in pitch To raise the pitch: Larger holes Decrease distance between holes and blow hole Additional holes outside the last open hole Decrease distance of cork from blow hole Thicker barrel requires larger holes for same pitch The smaller first open tone hole is, the more effect subsequent ones have in raising pitch Subsequent holes have less effect on higher registers 28

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Calculating effective lengths with corrections 29

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30 Octaves Low octave overtones are present even in the higher note

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31 Differences between plastic and wood recorders

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32 Wooden flutes Differences: Diameter Holes, size, placement Types of mouthpieces Material/type of wood Additional compromises Requiring fingers to cover holes No additional mouthpiece Material Restriction to one register

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33 Pan Pipes Solomon Islands – Pan pipes – from musical instruments of the world Breathy sound Closed end so an octave lower than a transverse flute

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34 End blown flutes- Algoza (Rajasthan) end blown, beveled end one drone one melody flute continuous blowing (circular breathing like the digeridu)

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35 Reed Instruments www.tufts.edu/as/wright_center/physics_2003_wkshp/book/

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36 www.tufts.edu/as/wright_center/physics_2003_wkshp/book/

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Harmonica Length of reeds set pitch Two sets of reeds, one for blow, other for draw 40

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41 Sardinian triple clarinet -- Launeddas

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42 Spectrum of oboe vs flute red is flute, green is oboe

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Excitation for reed instruments For excitation of tube of air trap door analogy for clarinet reed converting DC pressure into AC flow 43 image from http://www.phys.unsw.edu.au/jw/clarinetacoustics.html#reed

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Timbre depends on how hard you blow Blow pressure affects the shape of the airflow curve and so the timbre. Blowing harder increases the strength of higher harmonics. 44 image from http://www.phys.unsw.edu.au/jw/clarinetacoustics.html#reed

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Excitation of digi 45

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Other noises 46 sound recorded near mouth sound recorded in room

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47 Note: the shape of the mouthpiece is important as it affects the high frequency response of the instrument!

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48 Wooden trumpets Central African Republic Ongo ensemble of the Banda people consists of wooden and antelope horn trumpets

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49 Closed/open pipe Which instruments behave like closed ends? Clarinet, oboe, brass, some pan pipes? Which ones have open/open ends? Organ, flute, recorders, organ pipes We might expect odd integer overtones from the brass, however the bell at their end shifts the overtone spectra to nearly all integers

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Wavelength shift due to conical bore Easiest way to think of this is in terms of volume and air piling up at anti-nodes. Mouthpiece cuts off the end of the cone but is an approximate match to volume of that cone. 50

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51 Ocarinas More like Helmholtz resonators. Pitch is changed by adding holes

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52 Organ pipes Technological innovations led to improved air pumps in the late middle ages showcased in churches

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53 Types of organ pipes open/closed flue type – acoustics similar to flute but airflow is very important Reed type– tuned by adjusting length of reed – like the quack caller hunters use but with a more interesting resonator.

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Voicing of Craighead-Saunders Organ Christ Church (Episcopal) Eastman Rochester Organ Initiative by Munetaka Yokata (2008) Adjusting the depth and shape of the lip 54 The organ is a reproduction of a 1776 organ from Vilnius Lithuania this image from Oberlin to illustrate voicing

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Organ Pipe Voicing Delay of fundamental harmonic 55