PH 105

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PH 105
Hearing, power, loudness, auditory perception
Part 1
Dr. James van Howe Lecture 16
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Announcements
Lab make up sign up after class today
Two time slots Wednesday February 6, 400-600
pm Thursday February 7,
230-430 pm
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Name the Artist

• Dr. Dre
• Pfunk
• Snoop
• Eazy-E

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Going up in sound intensity by 3 dB means

• Going up by a factor of 3
• Going up by a factor of 2
• Going up by a factor of 1.5
• Not going up at all

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True or False
Elephants communicate at ultrasonic frequencies
too high for the human ear to hear
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The incredible human ear
Dynamic range of 1 trillion (120 dB)
Sound Level (dB)
Air displacement only a tenth the diameter of an
atom
Frequency range 20-20,000 Hz 10 octaves
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Frequency Range
20 Hz
20,000 Hz
Range of human hearing
Infrasound
ultrasound
Elephant communication (5-30 Hz)
Bat navigation 39-78 KHz
Bioacoustics lab Cornell
Very rare for a human to hear over entire
20-20,000 Hz range
Presbycusis age related hearing loss in high
frequency range
Many adults over 50 have trouble hearing past
12,000 Hz
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The mosquito a 17,000 Khz shrill sound device
was originally marketed by a Welsh security
company for shopkeepers to rid themselves of
loitering teenagers
Now used for text ring tones adults cant hear
A Ring Tone Meant to Fall on Deaf Ears New York
Times, June 12, 2006.
Presbycusis demo how high a frequency can you
hear?
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Intensity
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Sound Intensity
Units
Aside
Sound can radiate spherically just like light
from a light bulb
Note that if you move twice as far away from a
speaker, the intensity goes down by a factor of
four because of the 1/r2 dependence
Since the human ear can just barely hear 1
trillionth of a W/m2, all the way up to 1 W/m2
(one trillion times more!!!), we need a new
scaling system.
Otherwise we would need very long graph paper!!!
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Log scale saves the day

• Loge scale scrunches big numbers so we can view
  them on same graph as teeny ones
• Addition in log scale is just multiplication in
  linear scale
• Subtraction in log scale is just division in
  linear scale

Heres how they work
On your calculator Type 100 Type Log Should
show 2
Hint Just count the number of zeros (if on
bottom like 1/100, insert a minus sign)
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What is ?

• 3
• 4
• 5
• 6

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Now to Sound Level
Sound Level on the log scale is quoted in
decibels (dB)
Named for Alexander Graham Bell
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What do the dB mean?
Sound Intensity level (dB)
Example 0 Threshold of hearing 10
Rustling Leaves 20
Whisper 35 Library 45

Living Room 55
Office 68

Normal Conversation 74 Vacuum
Cleaner 85 Outboard Motor 95

Heavy Traffic 108 Motor Cycle
115 Rock Concert 120

Threshold of Pain 128
Machine
Gun 145
Jet at Take-off 155

Can burn skin 200
Noise Weapon
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Noise Weapon?
Long range acoustic device
Used for crowd control in Iraq
From CNN.com Troops get high-tech noise maker
March 3, 2004

• 33 inch dish points 2-3 kHz sound beam that is
  150 dB at 300 yds

• Meant as non-lethal crowd control, for no more
  than 2-3 second exposure

Unfortunately this is a sensitive region for
hearing loss more than a few seconds could give
permanent damage
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decibels in music
Sound Intensity level (dB)
Example 0 Threshold of hearing
30 ppp 50 p
(piano) 70
f
(forte) 90

fff 120

Threshold of Pain
Would seem to say that the dynamic range of
instruments is 60 dB
Not exactly true, Clarinet, trumpet, and violin
win in dynamic range 40-45 dB
Not all instruments can play both loud and soft
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Some tricks for Logs
Multiplying by 2 in the linear scale is the same
as adding 3 dB in the log scale
Twice as much
Twice as much as before (four times the original)
Twice as much as before (eight times the
original)
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Multiplying by 10 in the linear scale is the same
as adding 10 dB in the log scale
Ten times as much
Ten times as much as before (100 times the
original)
Ten times as much as before (1000 times the
original)
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The threshold of pain is 120 dB. What represents
twice as much intensity.

• 123 dB
• 126 dB
• 240 dB
• 243 dB

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The threshold of pain is 120 dB. What represents
half this intensity?

• 117 dB
• 123 dB
• 126 dB
• 60 dB

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The threshold of pain is 120 dB. What represents
ten times this intensity?

• 130 dB
• 140 dB
• 150 dB
• 1200 dB

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To make matters more confusing
Sometimes we reference sound to a pressure level
rather than intensity
Again referenced to threshold of hearing, in
pressure this time
Ten times much as before
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Logs on your stereo
The decibel scale is used on your stereo as well,
though not necessarily referenced to anything,
just gain (amount increased)
Turning volume up from -40 dB to -30 dB (adding
10 dB) means increasing the gain by 10 dB or
increasing the intensity by a factor of 10
Turning volume up from -30 dB to -27 dB (adding 3
dB) means increasing the intensity by a factor of
two
Weird thing about our ears is that what sounds
twice as loud doesnt correspond to 3 dB, but
more like 10 dB
Rule of thumb what sounds like twice as loud to
our ears is really ten times increase in
intensity (need 10 violins to sound twice as loud)
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Auditory perception experiment
Function generator, speaker, decimeter
(alternately stereo)
When does the tone sound twice as loud?
Is the rule of thumb ? it is subjective and not
universally agreed upon
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Frequency Sensitivity of human auditory system
Ears are more sensitive in certain frequency bands
40 dB SPL at 1,000 Hz sounds just as loud as 90
dB SPL (more than 300 times more) at 20 Hz
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The phon equal loudness unit
40 phons is actually 40 dB SPL at 1,000 Hz, and
the equivalent loudness of this tone everywhere
else (though actually higher and lower in SPL)
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Lets test our frequency sensitivity
Demo Function generator, speaker, decimeter
When does 50 Hz sound as loud as 1000 Hz?