sound audiology perry c. hanavan, au.d. audiologist
TRANSCRIPT
Propagation of Sound
Condensations____________
Example of molecular motionComponents of sinusoidTransverse wave simulationApplet: Square, triangle, simulation
Components of Sound
Physical Psychological
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Intensity Loudness
Frequency ________
Duration Length
Problem
Human hearing intensity dynamic range is quite broad
1 Softest sound
1,000,000,000,000 Loudest sound
Intensity Dynamic Range110100100010000100000100000010000000100000000100000000010000000000100000000000100000000000010000000000000100000000000000
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
Aha! Ratio Compare 2 Numbers1/1 =110/1 =10100/1 =1001000/1 =100010000/1 100000/1 1000000/110000000/1 100000000/1 1000000000/1 10000000000/1100000000000/11000000000000/110000000000000/1100000000000000/1
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 bel2 bels = 20 decibels
8 bels = 80 decibels
That was easy, let’s practice:
Integer: 10 X 10 = 100Log: 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: 100 / 10 = 10Log: 2 - 1 = 1
Integer: 1000000 / 100 = ?Log: 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 areaSPL: amount of pressure exerted on a 1cm2 surface areaIL = SPL2
dBIL=10logR equals dBSPL=20logR
dB Intensity Level
Measure of energy
Reference 1.0 X 10 -16 watts/cm2
or
.0000000000000001 watts/cm2
Ratios in IL and SPL
Sound Pressure Level
20/20 = 1:1
40/20 = 2:1
60/20 = 3:1
200/20 = 10:1
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
1.0x10-15/1.0x10-16
dBIL=10logR or dBSPL=20logR
Ratio No. Log dBIL dBSPL 1:1 1 0 0 02:1 2 .3010 3.0 6.03:1 3 .4771 4.8 9.64:1 4 .6020 6.0 12.05:1 5 .6990 7.0 14.06:1 6 .7781 7.8 15.67:1 7 .8451 8.5 17.08:1 8 .9030 9.0 18.09:1 9 .9542 9.5 19.010:1 10 1.000 10.0 20.0
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?