PH 105

1
PH 105
Percussion Follow-up, Woodwinds
Dr. James van Howe Lecture 13
2
Name the Artist

• Dr. Dre
• Pfunk
• Snoop
• Eazy-E

3
What mode is this?

• 1,2
• 2,1
• 3,2
• 2,3

4
True or False
Hitting a drum in the center produces long
ringing sound
5
True or False
Timpanis, and Tom-toms have enough whole number
overtones (harmonics) which is why they seem to
have pitch
6
A closed tube can support which harmonics?

• Even only
• Odd only
• Both even and odd
• Closed tubes cannot support whole number partials

7
A string can support which harmonics?

• Even only
• Odd only
• Both even and odd
• strings cannot support whole number partials

8
Below shows how the impedance curve changes when
tone-holes are added to a Clarinet.

True or False
When tone-holes are added we dont hear
frequencies above cut-off
9
The closer a tone hole becomes to the bore of the
instrument

• The more effect it has on shortening the length
• The less effect it has on shortening the a

10
High input impedance on an impedance curve means
that the particular frequency

• Has strong pressure wave at the bell
• Radiates well
• Has a strong pressure wave at the mouthpiece
• None of the above

11
True or False
Most of the sound from a wind instrument comes
from vibration of the brass or wood
12
True or False
Most of the sound energy from a violin or guitar
comes from the wood plates
13
Hint Waveforms of the Timpani for a center
strike.
122.7
147.3
245.5
Numbers show frequency in Hz of corresponding
partials (peaks)
387.8
186.5
314.2
Ratios using 147.3 Hz as principle
Close to textbook Timpani!
14
Instrument 3 Approximately 30 ms after the
strike.
147.3
216
417.3
466.4
289.6
353.5
392.7
Ratios using 147.3 Hz as principle
Almost textbook Timpani!
-Though textbook, ratios arent that great.
-Based on whole number rule, pitch should be
unclear
Fundamental is same frequency as the principle in
the hint, good clue that this is Timpani for
normal strike
15
Instrument 2 Approximately 30 ms after the
strike. Unlike instrument 1, the spectrum does
not change very much as the sound decays.
314.2
1261.7
Numbers show frequency in Hz of corresponding
partials (peak)
628.4
937.7
Ratios using 314.2 Hz as principle and
fundamental
Very harmonic, throughout ring indicates pitch
through whole duration, most likely Marimba
Fundamental 1st mode in spectrum Principle mode
the mode you hear
16
Instrument 1 Just after the strike.
157.1
333.8
Numbers show frequency in Hz of corresponding
partials (peaks)
697.1
481.1
618.6
Ratios using 157.1 Hz as principle and
fundamental
Very harmonic, indicates pitch at the beginning
17
Instrument 1 Approximately 30 ms after the
strike.
157.1
294.6
417
319.1
Numbers show frequency in Hz of corresponding
partials (peaks)
471.3
378
240.5
Ratios using 157.1 Hz as principle and
fundamental
Not as harmonic as right after strike, some
integer ratios slightly messier than Timpani near
mode 3 and 4 indicates Tom Easy to confuse with
Timpani were it not for 0.85 ratio of principle
to fundamental mode in Timpani.
18
Summary of Activity
Hypothesis If instruments spectra contain
enough harmonic content this indicates that
they have definite pitch

• Hint gives away Timpani center strike this means
  that the very first mode is 0,1 and so mode 1,1
  must be at 147.3 Hz
• For a normal strike, we should see very little
  (maybe no 0,1) and a strong 1,1 mode at 147.3 Hz,
  this is shown in instrument 3
• Sure enough ratios of frequencies in hint and
  Instrument 3 are pretty close to what text has
  for Timpani
• Instrument 2 very harmonic for entire duration
  indicates Marimba
• That mean Instrument 1 must be the Tom
• Interesting is that spectrum is very harmonic at
  the beginning
• Secondly, though spectrum looses harmonic content
  after Tom rings, it is unclear with the brief
  analysis whether it has a better or worse
  harmonic relationship than Timpani

19
Reeds
Blowing over reed causes it to flap up and down,
letting puffs of air in and out at a regular
frequency like lips of brass player
Bernoulli Effect Increase flow in velocity
results in lower pressure
Self demo take two strips of paper and blow
between them, What happens?
Ever notice this when passing a big semi-truck on
the highway?
20
Vibration of Pipe-Reed
Puff air lowers pressure reed brought up-wards
negative pressure under reed pushes it down-wards
Positive pressure
negative pressure
One cycle of reed
negative pressure pulse closes reed
Positive pressure pulse opens reed so that
another puff can be introduced
21
Lips vs. Pipe-reed

• Lips more versatile, pipe-reed cant easily be
  set into motion at any frequency
• Play a tune on trumpet (brass) mouthpiece
• Now try clarinet (reed instrument) mouthpiece

Clarinet needs tube an bell much more than trumpet
22
Air reed flute, whistle
Flow control valve rather than pressure-control
reed
reed
Oscillation of the air reed on bottle
reed
reed
flute cross section
Oscillation of the air reed on a flute
Air jet is like reed. To play fundamental, air
reed sweeps across opening twice for one full
cycle of the pressure wave
23
Changing register on flute

• Blowing pressure higher pressure, higher pitch-
  whistling tea kettle
• Length of air jet smaller length higher pitch
• Lip opening reduce for higher pitch

reed
reed
Insert 12.3
flute cross section
Oscillation of the air reed on a flute
24
Valves, slides, tone holes

• Used to dynamically change the effective length
  of tube and therefore pitch

Mouth Piece
Bell
L
Demo slide whistle
25
Acoustic Impedance
Impedance sort of like density, if there is a
mismatch, waves reflect back
Example because of a density mismatch between
glass and air, light reflects off glass this is
why you can see a faint reflection of yourself in
a window pane
If impedance changes over length of tube,
reflection occurs
Bell sends pressure wave back to mouth piece
since impedance mismatch
Inside trumpet reflected waves build up, 100x
louder than a jet
26
Valves
On trumpet without valves, eight notes can be
played few more for skilled players
No valves, 8 strong notes
longer tube
shorter tube
Pushing down valves make tube longer, so
wavelength longer, or pitch lower
27
Slides
-Note how seven positions give you all the notes,
but there are twelve notes on a scale, and the
trombone can even hit multiple octaves.
What must a trombonist do to play additional
notes/octaves?
-Note how the seven positions are not equally
spaced, scaling is logarithmic!
28
Valve length problems
- If valves add same length, cant get all notes,
but if not same length certain valve combos
make notes sharp or flat
Solution For trumpet, corrector on third valve
during playing player must lip the rest to be in
tune
29
Tone-Holes
- Tone holes not only help change pitch, but
radiate sound along with bell
- When tone-hole diameter matches bore diameter
tube effectively ends at hole
- Larger tone-hole shorter tube shorter
wavelength higher pitch
Bell
L
L
Mouthpiece
30
Many periodic tone-holes make up tone hole
lattice
Tone-hole lattice filters acoustical frequencies
Tone-hole
Bore
Tone-hole spacing
Effect of tone holes is to radiate out higher
frequencies
31
Impedance Curves for Clarinet
All tone holes closed closed pipe
Rest of curves tone-hole lattice radiates away
higher harmonics
32
A closed tube can support which harmonics?

• Even only
• Odd only
• Both even and odd
• Closed tubes cannot support whole number partials

33
A string can support which harmonics?

• Even only
• Odd only
• Both even and odd
• strings cannot support whole number partials

34
Below shows how the impedance curve changes when
tone-holes are added to a Clarinet.

True or False
When tone-holes are added we dont hear
frequencies above cut-off
35
The closer a tone hole becomes to the bore of the
instrument

• The more effect it has on shortening the length
• The less effect it has on shortening the a

36
High input impedance on an impedance curve means
that the particular frequency

• Has strong pressure wave at the bell
• Radiates well
• Has a strong pressure wave at the mouthpiece
• None of the above

37
True or False
Most of the sound from a wind instrument comes
from vibration of the brass or wood
38
True or False
Most of the sound energy from a violin or guitar
comes from the wood plates