SoundAudiology

Perry C. Hanavan, Au.D.

Audiologist

Sound

Vibration

Perception

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

Intensity

Decibel– Unit of measure of intensity– dB = 10logR (R=ratio)– dB = 20logR

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

Solution

Ratio

Compare intensity value (number) to reference

8:4 (really 2:1)

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

Logarithms!!

Now that a ratio has been converted

Next step: Convert ratios to logs (base 10)

Lets Work with Logs!!!

1 = 010 = 1100 = 2100000000000000 = ?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 bel2 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 = 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

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

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

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)