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 PhysicalPsychological IntensityLoudness Frequency________ DurationLength
Intensity Decibel –Unit of measure of intensity –dB = 10logR (R=ratio) –dB = 20logR
Problem Human hearing intensity dynamic range is quite broad 1Softest sound 1,000,000,000,000Loudest sound
Intensity Dynamic Range
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 = /1 = / / / / / / / / / / /1
Logarithms!! Now that a ratio has been converted Next step: Convert ratios to logs (base 10)
Lets Work with Logs!!! 1 = 0 10 = = = ? 14.1 = = = ? -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: = 2 Integer: 1000 X 1000 = ? Log: = 6 Now take the log times 10 to convert to decibels
Not bad, let’s try this: Integer:100 / 10 = 10 Log: = 1 Integer: / 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 1cm 2 surface area SPL: amount of pressure exerted on a 1cm 2 surface area IL = SPL 2 dB IL =10logR equals dB SPL =20logR
dB Intensity Level Measure of energy Reference 1.0 X watts/cm 2 or watts/cm 2
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 1.0x /1.0x x /1.0x x /1.0x x /1.0x x /1.0x10 -16
dB IL =10logR or dB SPL =20logR Ratio No.Log dB IL dB SPL 1: : : : : : : : : :
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)