Transcript Introduction to Audiology Chapter 2 Sound

Sound
Audiology
Perry C. Hanavan, Au.D.
Audiologist
Sound
Vibration
Perception
Propagation of Sound
Condensations
____________
Example of molecular motion
Components of sinusoid
Transverse wave simulation
Applet: Square, triangle, simulation
Components of Sound
Physical
Psychological
------------------------------------Intensity
Loudness
Frequency ________
Duration
Length
Intensity
Decibel
– Unit of measure of intensity
– dB = 10logR
(R=ratio)
– dB = 20logR
Problem
Human hearing intensity dynamic range is
quite broad
1
1,000,000,000,000
Softest sound
Loudest sound
Intensity Dynamic Range
1
10
100
1000
10000
100000
1000000
10000000
100000000
1000000000
10000000000
100000000000
1000000000000
10000000000000
100000000000000
Honey I Shrunk the Kids
1,3,5 or 1, 4, 8, 12 etc. reduces dynamic
range somewhat
1, 10, 100, 1000 shrinks a bit more
– Yet, dynamic range is quite large
Solution
Ratio
Compare intensity value (number) to
reference
8:4 (really 2:1)
Aha! Ratio Compare 2 Numbers
1/1 =1
10/1 =10
100/1 =100
1000/1 =1000
10000/1
100000/1
1000000/1
10000000/1
100000000/1
1000000000/1
10000000000/1
100000000000/1
1000000000000/1
10000000000000/1
100000000000000/1
Logarithms!!
Now that a ratio has been converted
Next step: Convert ratios to logs (base 10)
Lets Work with Logs!!!
1=0
10 = 1
100 = 2
100000000000000 = ?
14
.1 = -1
.01 = -2
.00000000001 = ?
-11
So is that a decibel?
So far we have
1. Converted a ratio to a number (10:1=10)
2. Converted the ratio to a log (10=1)
We have created a ____ (A.G. Bell)
There are 10 decibels in a bel
2 bels = 20 decibels
8 bels = 80 decibels
WOW!!!
Decibel = 10 log _____
A decibel consists of:
1. Ratio
2. Log
3. X10
That was easy, let’s practice:
Integer: 10 X 10 = 100
Log:
1+1 = 2
Integer: 1000 X 1000 = ?
Log:
3+3=6
Now take the log times 10 to convert to
decibels
Not bad, let’s try this:
Integer:
Log:
100 / 10 = 10
2-1 =1
Integer:
Log:
1000000 / 100 = ?
6–2=4
Now take the log times 10 to convert to
decibels
Ok, I can do that, but…
Some numbers are quite easy to work with
in logs
However, some numbers you need to use
a calculator or look in a CRC book of
tables
Or you can memorize several numbers
and calculate lots of logs
Hint: log = bel
Oh, one more thing:
Measures of ________ are often made in
Sound Pressure Level (SPL) rather than
Intensity Level (IL)
IL: amount of energy flowing thru a 1cm2
surface area
SPL: amount of pressure exerted on a
1cm2 surface area
IL = SPL2
dBIL=10logR equals dBSPL=20logR
dB Intensity Level
Measure of energy
Reference
1.0 X 10 -16 watts/cm2
or
.0000000000000001 watts/cm2
dB Sound Pressure Level
Measure of force or pressure
Reference
20 microPA
Ratios in IL and SPL
Sound Pressure Level
20/20 = 1:1
40/20 = 2:1
60/20 = 3:1
Intensity Level
1.0x10-16/1.0x10-16
2.0x10-16/1.0x10-16
3.0x10-16/1.0x10-16
4.0x10-16/1.0x10-16
200/20 = 10:1
1.0x10-15/1.0x10-16
dBIL=10logR or dBSPL=20logR
Ratio
1:1
2:1
3:1
4:1
5:1
6:1
7:1
8:1
9:1
10:1
No.
1
2
3
4
5
6
7
8
9
10
Log
0
.3010
.4771
.6020
.6990
.7781
.8451
.9030
.9542
1.000
dBIL
0
3.0
4.8
6.0
7.0
7.8
8.5
9.0
9.5
10.0
dBSPL
0
6.0
9.6
12.0
14.0
15.6
17.0
18.0
19.0
20.0
Can you do this?
Double SPL?
Double IL?
Triple SPL
Triple IL?
Quadruple SPL?
Quadruple IL?
What about this?
Halve IL?
Halve SPL?
Practical Applications of dB
If a child’s ear canal is ___ times as small
as an adult, what happens to the SPL in
the child’s ear canal?
If a student is 3 times closer to the
teacher’s voice than another, how much
more SPL reaches the child sitting near
the teacher?
Hearing Level
Converting SPL to HL (HTL)