Class Notes November 7. Reed instruments; The woodwinds

Transcription

1 The Physics of Musical Instruments Class Notes November 7 Reed instruments; The woodwinds 1

2 Topics How reeds work Woodwinds vs brasses Finger holes a reprise Conical vs cylindrical bore Changing registers Role of the bell Woodwind timbre Clarinet demonstration 2

3 Return to the Water Trumpet The critical component is the pressuresensitive valve a reed works exactly this way 3

4 Reeds and Mouthpieces Single reed on a mouthpiece Clarinet, saxophone, basset horn Double reed mounted on a tube Oboe, bassoon, English horn 4

5 Clarinet Mouthpiece We pass around a clarinet mouthpiece with a reed attached See how easily the reed can be pressed to close the gap BUT When the air pressure inside the instrument is at its maximum, it can force the reed to open up a little and let in some air an ideal example of the pressure-activated valve. 5

6 Topics How reeds work Woodwinds vs brasses Finger holes a reprise Conical vs cylindrical bore Changing registers Role of the bell Woodwind timbre Clarinet demonstration 6

7 Two kinds of reeds Lip reeds Brass instruments The lips have a huge influence on which tone is reinforced, and can even select the tone with ease Wooden reeds Woodwind instruments The instrument cavity has the greatest influence on which tone is reinforced more in this later The reed is essential, but it is not tone-selective without a lot of work by the player (I will demonstrate later) 7

8 Topics How reeds work Woodwinds vs brasses Finger holes a reprise Conical vs cylindrical bore Changing registers Role of the bell Woodwind timbre Clarinet demonstration 8

9 Impedance Again Tiny discontinuity in impedance; weak reflection Big discontinuity in impedance; strong reflection Resonance determined by pipe length Resonance determined by hole position 9

10 Side Holes add Reflections The side holes add small cavities that makes the resonator no longer a simple ideal pipe Added volume and mass, like Benade s assembly of bottles Impedance bumps even when the hole is closed 10

11 How Many Holes are Needed? Enough to span from the lowest note to the first important harmonic that can be made to sound And that depends on the BORE of the instrument 11

12 Topics How reeds work Woodwinds vs brasses Finger holes a reprise Conical vs cylindrical bore Changing registers Role of the bell Woodwind timbre Clarinet demonstration 12

13 The Clarinet has a Cylindrical Bore Behaves like a pipe closed at one end High pressure at the mouthpiece Low pressure at the bell 13

14 Closed Cylindrical Bore A cylindrical bore woodwind (ie the clarinet) only supports the odd harmonics It cannot support even harmonics, as that would require a node at the mouthpiece and air is injected only at pressure maximum, not at a node. 14

15 The Interval is a Twelfth The third harmonic of a pitch is an octave plus a fifth above the fundamental pitch The interval is called a twelfth When you include the half-steps, it takes a lot of holes to cover the twelfth. You need 18 separate lengths to get a complete chromatic scale that covers a twelfth. That s a lot of holes 15

16 Conical Bores are Different In a conical bore, a supported vibration can have a node very close to the end As a result, a conical bore supports both even and odd harmonics of the fundamental Only one octave worth of holes is needed, just like on the flute. Oboe, saxophone, and bassoon have conical bores 16

17 Conical Bore Cross Sections Oboe, saxophone, and bassoon cross-sections, with the diameters greatly exaggerated Each of these instruments have the octave as the first harmonic that can sound 17

18 Making Scales Clarinet Oboe Flute 18

19 Topics How reeds work Woodwinds vs brasses Finger holes a reprise Conical vs cylindrical bore Changing registers Role of the bell Woodwind timbre Clarinet demonstration 19

20 How to Change Registers Brass dominated by the player s lips Tighten, and one can select a harmonic Reed instruments dominated by the cavity The technique is to add one or more holes, called speaker holes (or octave keys ) near the reed that tends to suppress the fundamental, and allows the next register to sound. The clarinet has one such key; the oboe has three 20

21 Topics How reeds work Woodwinds vs brasses Finger holes a reprise Conical vs cylindrical bore Changing registers Role of the bell Woodwind timbre Clarinet demonstration 21

22 Bell Affects Lowest Notes We will examine this when we do the demonstration, but when enough holes are open, the bell has little impact on the sound The sound emanates from the open holes except when most of the holes are closed We will compare the clarinet played with and without a bell, but first, we examine the recipe differences of the reed woodwinds 22

23 Topics How reeds work Woodwinds vs brasses Finger holes a reprise Conical vs cylindrical bore Changing registers Role of the bell Woodwind timbre Clarinet demonstration 23

24 Recipes Low Register Middle Register Oboe Saxophone Saxophone Clarinet Clarinet 24

25 Topics How reeds work Woodwinds vs brasses Finger holes a reprise Conical vs cylindrical bore Changing registers Role of the bell Woodwind timbre Clarinet demonstration 25