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What is power?
 the rate at which energy is transferred; energy transferred per unit time
 energy per second

What is energy?
the capacity to do work, whereas power is the rate at which energy (the work) is expended (done)

What is a Watt?
 energy transferred per unit time
 1 watt = 1 joule/s

What is a relative measure?
a comparative measure

What is an absolute measure?
an exact number or amount

What unit of measure is power expressed in?
 watts
 sound = 2 x 10^8 watts (.00000002)

What is relative measure of power?
 absolute power in one sound wave is compared with absolute power in another (reference) wave
 A = 2B or B = A/2

What is intensity?
energy per second per square meter

What is the unit of measure of intensity?
watt/m2

What is I_{x}?
absolute intensity

What is I_{r}?
reference intensity

What is the ratio for the level of intensity?
I_{x}/I_{r}

What is a Bel?
 the log of the ratio I_{x}/I_{r}
 Bels = log_{10}(I_{x}/I_{r})
 if the base is not give, assume it is 10

What do positive bels mean?
the absolute measure is bigger than the reference

What do negative bels mean?
the absolute measure is smaller than the reference


I_{x }= 10^{6} watt/m^{2}
I_{r} = 10^10 watt/m^2
What is the absolute intensity?
What is the level of intensity in bels?^{ }

How do you go from bels to decibels?
 bels = log_{10}(2 x 10^{8}/ 10^{12})
 bels = 4.3 = 43 decibels (dB)
 to convert from bels to decibels, multiply by 10

What is the equation for dB?
 10log_{10}(Ix/I_{r})
 a decibel is 10 times the log of an intensity ratio or of a power ratio

Sample dB problems page 53 slide 26

For every 10fold change in I_{x}, dB changes by? Why?
 10 dB
 log_{10}10 = 1; 1 x 10 = 10

For every 2fold change in I_{x}, dB changes by?
3 dB

What do 0 decibels mean?
I_{x} = I_{r}

What is dB IL?
 intensity level
 the reference intensity must always be specified!

What is the standard reference intensity for dB IL?
I_{r} = 10^{12} watt/m^{2}

dB IL problems page 54 slide 31

Sample problems page 54 and 55

What are the four types of intensity problems?
 given an intensity ratio, calculate decibels
 given decibels, calculate intensity ratio
 given I_{x}, calculate dB IL
 give dB IL, calculate I_{x}

What is sound pressure?
force/unit area

What is the unit of measure for pressure?
 N/m^{2} = 1 Pa
 microN/m^{2} = 1 microPa

What is impedance?
an opposition to motion

What is the relationship between intensity and pressure?
 I is directly proportional to p^{2}
 p is directly proportional to the square root of I^{ }

How much does p increase if I increases by some factor?
p increases by the square root of that factor

What is the equation for sound pressure?
20log_{10}(P_{x}/P_{r})

Pressure sample problems page 58 and 59

What are the four types of pressure problems?
 given a pressure ratio, calculate decibels
 given decibels, calculate pressure ratio
 given p_{x}, calculate dB SPL
 given dB SPL, calculate p_{x}

What is the relationship between dB IL and dB SPL?
they are equal

If two sounds have an intensity level of 60 dB IL each thatn what is the total intensity level of them?
63 dB IL

When you double intensities how much does it increase by?
3 dB

Combining intensities page 63

*If intensity doubles, dB increases by 3, which means pressure also increases by 3. If we are ONLY talking about pressure, not intensity, dB increases by 6

What is the equation for equal source intensities?
 dB_{N} = dB_{i} + 10log_{10}N
 i = dB SPL (or dB IL) from one source (only add intensities so use 10logX)
 N = # of sources combined

Two sources each produce 100 dB SPL. What is the total SPL?
 dB = 100 + 10log2
 = 103 dB SPL

Three sources each produce 100 dB SPL. What is the total SPL?
 dB = 100 + 10log3
 = 104.8 dB SPL

Eight sources each produce 91.2 dB SPL. By how many dB is SPL increased?
 dB = 10log8
 = 9 (100.2  91.2)
 *not asking for total
 *talking about ratios

