Phys 1240: Sound and Music
www.colorado.edu/physics/phys1240
LAST TIME: Exam.
TODAY: Ears and Hearing
NEXT TIME: Hearing and sound perception
READ: finish chapter 6
• Homework 8 and Reading Question 10 due
Thursday.
• Midterm grades (including all work pre-exam
2) posted to D2L.
– Clicker question score included.
• Exam 2 scores and answers posted to D2L.
Exam 2 scores
• Median score: 69
• Standard deviation: 14
• Curved scale:
– 89-100 A
– 77-88 B
– 65-76 C
– 53-64 D
– 0-52 F
• LAs are writing up solutions to parts
of exam – will be posted to D2L
OUTER
MIDDLE
INNER
Middle ear
http://www.cochlea.org/en/the-ear.html
Amplification in the middle ear
Eardrum ~20 times larger (in area) than
oval window.
If the force is same on either end of the
ossicles, the pressure on the oval
window is ~20 times larger than on the
eardrum.
Lever effect:
The malleus moves 30% more than
the stapes
Force on the oval window is 30%
more than force on the eardrum.
Even more pressure amplification!
Inner ear
• Vibrations from
oval window
transmitted to
fluid of inner ear
• Basilar
membrane
oscillations
• Positiondependent
resonance!
http://www.cochlea.org/
Spatially dependent frequency
response of basilar membrane
http://www.blackwellpublishing.com/matthew
s/ear.html
Hair cells in basilar membrane
http://www.cochlea.org/en/the-ear.html
http://www.beyonddiscovery.org/content/view.page.asp
?I=259
Hair cells
Clicker question
What physical mechanism most helps you
perceive “pitch”?
A) Direct coupling of vibration rate of hair cells
to signal strength
B) Location of vibrating hair cells carries
frequency information
C) Amplitude of vibration of hair cell carries
frequency info
D) Entirely done at the level of “brain signal
processing”
Sound perception
JND = “just noticeable difference”
(psychophysics)
JND in sound level (which depends on
frequency and sound level!)
JND in frequency (which depends on
frequency and sound level!)
http://www.phys.unsw.edu.au/jw/dB.html
A typical JND is about 1 dB.
What percent change is that in the intensity?
A) 1%
D) 30%
B) 1.3%
E) 100%
S IL difference
(in decibels)
1 dB
2 dB
3 dB
4 dB
5 dB
6 dB
7 dB
8 dB
9 dB
C) 13%
Intensity
ratio
1.3
1.6
2.0
2.5
3.2
4.0
5.0
6.3
7.9
JND curves
0.5
JND (dB)
1.5
8 kHz
200 Hz
1000 Hz
40
Sound Intensity Level (dB)
80
JND (dB)
1.5
8 kHz
0.5
200 Hz
1000 Hz
40
80
Sound Intensity Level (dB)
If a singer has trouble holding the loudness of a note
perfectly, but she still wants to impress her audience
with a demonstration of steady loudness, it’s better for
her to:
A) Sing quietly and low pitched
B) Sing quietly and high pitched
C) Sing loudly and low pitched
D) Sing loudly and high pitched
JND (dB)
8 kHz
200 Hz
1000 Hz
40
80
Sound Intensity Level (dB)
If a singer has trouble holding the loudness of a note
perfectly, but she still wants to impress her audience
with a demonstration of steady loudness,, it’s better for
her to
A) Sing quietly and low pitched
B) Sing quietly and high pitched
C) Sing loudly and low pitched
D) Sing loudly and high pitched
E) Something else
Hearing response curves
• http://www.phys.unsw.edu.au/jw/hearing.ht
ml
• What are some limitations of the way we
have done this experiment?
SIL (deciBels)
100
0
100
1000
Frequency (in Hz)
10k
What loudness and frequency are at this point
indicated by the dot and arrow on the graph?
A) 100 Hz, 100 dB
B) 1000 Hz, 100 dB
C) 10,000 Hz, 100 dB
D) 1000 Hz, 50 dB
E) 100 Hz, 50 dB