Phys 1240: Sound and Music
LAST: resonance, and percussion
instruments
TODAY: string, and wind instruments
NEXT: Exam. See web for details
READ: Nothing new for Thursday.
For a week from now, 4.1, then 4.5
(though, we won’t really discuss
refraction much. We’ll come back
to 4.2/4.3 NEXT).
CT 3.3.1a
Which lasts longer, the vibration of a
string on an electric guitar, or on an
acoustic guitar?
(Assume the same string, plucked
the same)
A) Electric guitar strings vibrate
longer
B) Acoustic guitar strings vibrate
longer
C) Both should vibrate the same
D) ???
Study session - Ramaley
RAMY C-250 Wed evening, 7-9!
CT 3.4.3a
CT 3.3.2
If I shorten the string of this instrument what
happens?
How do you raise the pitch of a string
instrument by exactly one octave?
a)
b)
c)
d)
e)
a)
The pitch goes up
The pitch goes down
The sound gets louder
The sound gets quieter
More than one of these
What if I increase the tension?
b)
c)
d)
Put your finger down exactly halfway
along the string
Put your finger down somewhere else
Increase the tension by a factor of 2
More than one of these
Freq (SHM) = const * √ (K/mass)
λ * freq = speed of wave
= const* (√ Tension/mass)
Does this same idea work for percussion
instruments (like a drum head?)
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Octaves
Doubling the frequency produces a tone which is
“the same” (sort of!)
=> It’s one octave higher
Same NAME (e.g. middle C, go up by a factor of 2
in frequency, you’re back to C again)
WHY?
CONNECTION TO LENGTH?
(metal bars: speed of transverse waves depends
on wavelength!)
Strings
Things to think about:
• Effect of tension (or string
mass, or string length)
• Frets
• Extra (resonating) strings (e.g.
triple strings on piano)
• Coupling vibrations to air (!!)
• Plucking vs sustaining (bows)
CT 3.4.3b
How do you raise the pitch of a wind instrument
by exactly one octave?
a)
b)
c)
d)
e)
Halve the effective length of the tube
Change the length, but not by 1/2 (!)
Halve the diameter of the tube
Blow half as hard
More than one of these
CT 3.4.1
A long tube produces a sound
If I cut the tube in half, the pitch will be…
compared to the original
a)
b)
c)
d)
e)
Higher by an octave
Higher, but not by an octave
Lower
Lower, but not by an octave
the same as
What if I make the diameter of the tube larger?
What if I blow harder?
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CT 3.4.2
What is the function of finger holes in a flute?
a)
b)
c)
d)
e)
To create an edgetone
To shorten or lengthen the pipe
Emphasizes the affects of the reed
Mostly aesthetic
More than one of these
CT 3.4.3
If we halve the length of a tube in a wind
instrument what will happen?
a)
b)
c)
d)
e)
The period is halved
The frequency is doubled
Raises the pitch one octave
Both a and b
a, b, and c
CT 3.4.4
f * λ = speed
CT 3.4.x
If “f” refers to the vibrational
frequency of the string, and λ is
the wavelength of the wave on
the string, what is the relevant
“speed” for a string instrument?
A) 344 m/s
B) Something totally different!
What is the function of the flared bell on the end
of a recorder?
a)
b)
c)
d)
e)
It aids in projecting the music
It slows the speed of the sound being
produced
It lowers pitch of the note
It is mostly for visual effect
Some other important function
Same question, but referring to the
Pressure vibrations inside a wind
instrument?
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CT 3.5.1
Winds
What is the key difference between a flute and
a recorder?
•Resonating chamber
Cylindrical
vs
conical
a)
b)
c)
d)
e)
• Edgetones (flute, recorder, organ)
vs Reeds
single (clarinet: cylindrical sax: conical)
or double (oboe, bassoon)
One of them has a reed and the other does not
One makes use of an edgetone and the other does
not
One of them has a double reed and one has a
single reed
Something else
More than one of the above
What is the key difference between an oboe
and a clarinet?
• Woodwinds (all the above) vs
Brass (mouthpiece/lips)
• Voice (kind of like brass!)
CT 3.3.1b
The sound that you hear from a violin
is produced by:
a) Mostly strings
b) Mostly the wood in the back
c) Both equally
d) None of the above
“You can’t fan a fire
with a knitting needle”
CTR
• What is sound? How do you describe it
microscopically? How do you represent it
graphically?
• How are frequency, wavelength, period,
amplitude, speed, loudness, pitch,
pressure,… Defined? Related? What
do they depend on? Why?
• Simple harmonic motion, and the
(metaphorical?) connections to sound
• What experiments have we done to
demonstrate/make sense of these
properties and relations?
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CTR1.2
CTR1.1
A traveling wave moves along a
string. A given “peak” moves along
the full 5 m long string in 1 sec
Amplitude
A singer holds a note, singing into a
microphone which is plugged into an
oscilloscope. The trace is shown below.
What is the frequency of the sung note?
Volts
0.1
.1 m
0
Time (sec)
1
2
3
3
This graph shows the height of a
small spot on the string as the
traveling wave moves along. What’s
the wavelength of this wave?
A)10 m
D) 0.1 m
B) .67 m
E) 2.5 m
C) 2 m
CTR1.3
You’re clapping in front of a wall, a
distance “D” away from you. The
pattern is
clap-pause-echo-pause-clap-pause-echo…
(evenly spaced… picture it!)
Your friend times your claps (not the
echos!) and counts 6 claps in 10
seconds.
What’s the speed of sound?
m sec
A)1 Hz
B)2 Hz
C)500 Hz
D)1000 Hz
E)Something else/not sure
TR1.4
A singer is singing into a
microphone which is plugged into
an oscilloscope. They are singing
at a constant pitch (“concert A”)
but getting steadily louder and
louder. What would the ‘scope
trace look like?
What if they are singing at a
Steady volume, but getting
higher and higher in pitch?
A) 4 D / (0.6 sec)
B) 2 D / (0.6 sec)
C) D / (0.6 sec)
D) 10 D / (.6 sec)
E) D / (1.2 sec)
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Physlets
Physlet: periodic motion
Physlet: waves/superposition
Physlet: sound
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