Comd 3400 Acoustics Exam I

Front 1

a pressure wave which consists of vibrations of an elastic medium (gas-liquid-solid); (exerts pressure on the tympanic membrane)

Back 1

Sound

Front 2

any object with the properties of inertia and elasticity may be set into vibration and therefore create sound; the movement of an object from one point in space to another point and usually back again to the original point

Back 2

Vibration

Front 3

How does sound differ from other vibrating motions

Back 3

Sound waves in free air are THREE DIMENSIONAL.
Sound in air is propagated as a LONGITUDINAL WAVE. (domino effect)

Front 4

waves of greater than atmospheric pressure

Back 4

compression

Front 5

waves of lesser than atmospheric pressure

Back 5

rarefaction

Front 6

number of cycles per second (frequency) is measured in?

Back 6

Hertz

Front 7

a force that will accelerate 1 kg of mass a distance of 1 meter per second
UNIT OF FORCE Measurement

Back 7

Newton
remember eraser across the desk example

Front 8

1 of these - 10 deci of these

Back 8

Bel

Front 9

unit of sound pressure, and is equal to _____

Back 9

Pascals (Pa), 1 Pa = 1 N/M squared
1 pascal = one newton per square meter

Front 10

Range of human hearing is a range of __ Bels or __ decibels

Back 10

14
0-140 deciBels

Front 11

sine wave

Back 11

Simple Sound Wave

Front 12

amplitude is measured in

Back 12

decibels

Front 13

The distance in feet between identical points on 2 adjacent _____ is _________

Back 13

waves is wavelength

Front 14

how often, within a given amount of time, we complete one vibration or one cycle. It is also the number of complete cycles per second.

Back 14

Frequency (f)

Front 15

SPEED at which the energy travels from the source to the ear is the

Back 15

Velocity

Front 16

the ____the wavelength, the higher the frequency; the _____ the wavelength, the lower the frequency

Back 16

shorter, longer

Front 17

What is this formula? 1/T
If T = .001, then what is the computation?

Back 17

frequency
=
1000Hz

Front 18

a disturbance, vibration, that is capable of being heard

Back 18

Sound

Front 19

transfer of energy from one location to another

Back 19

Sound

Front 20

If we hear a vibration, then the sound is ___________

Back 20

audible

Front 21

force on the object to make it move

Back 21

inertia

Front 22

the ability of the object to return to a starting state after it is deformed or moved

Back 22

elasticity

Front 23

almost every object has inertia and elasticity - therefore almost every object can be set into ______________

Back 23

vibration

Front 24

tendency for matter at rest to remain at rest
or
tendency for matter in motion to remain in motion

Back 24

inertia

Front 25

must have mass and be compressible (have elasticity)

Back 25

sound medium

Front 26

types of waves in the air with compressions and rarefactions

Back 26

longitudinal waves

Front 27

disturbance that moves is ____, not the ______

Back 27

sound propagation, medium

Front 28

Simple sound waves have 3 parameters:

Back 28

amplitude, frequency, starting phase

Front 29

size of change from 0 compression and rarefaction

Back 29

amplitude -***

Front 30

one compression and rarefaction =

Back 30

one cycle

Front 31

number of complete cycles per second

Back 31

frequency

Front 32

20 Hz - 20,000 Hz is

Back 32

range of human hearing

Front 33

term used to describe the time required to generate one cycle of a sine wave

Back 33

period

Front 34

T=1/f

Back 34

Period (T = Time)

Front 35

low frequency has a _____ period and a ______ pitch

Back 35

long, lower

Front 36

A high frequency sounds has a _____ period and a _____ pitch

Back 36

short, higher

Front 37

Period of a 10,000 Hz tone

Back 37

T=1/10,000 = .0001 second

Front 38

=C/f
where C = ?

Back 38

wavelength, speed of sound, 1130 feet per second or 344 meters per sec

Front 39

wavelength of 113 Hz tone is?

Back 39

10 feet

Front 40

= C/wavelength (^)
1130/2.26 =

Back 40

Frequency, 500 Hz

Front 41

What is this formula? f * wavelength
and if f is 500
and wavelength is 2.26, then
500 * 2.26 =

Back 41

C (speed of sound), 1130 ft/sec

Front 42

Speed of sound in air

Back 42

velocity, 1130 ft per second or 344 meters per second

Front 43

degrees of angle

Back 43

phase

Front 44

Describe Phase angles on compression and rarefaction period (uniform circular motion)

Back 44

where is 0, 90, 180, 270, 360 (any of these can be starting points)

Front 45

point in the cycle at which the object begins to vibrate

Back 45

starting phase

Front 46

2 or more sine waves or pure tones are combined

Back 46

complex wave (study slide 3 acoustics II)

Front 47

exact same tones maybe combined in different ways depending on _________ ____________

Back 47

phase relationships

Front 48

Tone One: Phase angle = 0, compression is +4, rarefaction is -4
Tone Two: Phase angle = 180, rarefaction = -4, compression = +4
when combined?

Back 48

straight line, ear is not sensitive to this

Front 49

-no repeating pattern of a complex wave
-greater irregularity in wave form
-unwanted, noisy sound
-can have components at all frequencies and no multiple of fundamental frequency

Back 49

aperiod sound, noise

Front 50

all frequencies are represented at equal intensities,
flat spectrum

Back 50

white noise

Front 51

white noise that has been shaped to yield equal intensity per octave (3dB)
-intensity goes down as frequency goes up

Back 51

pink noise

Front 52

good for masking speech in audiometric testing
approximates long time average speech spectrum

Back 52

Speech Spectrum Noise

Front 53

White noise that has been band-pass filtered such that only narrow band of frequencies is presented
-excellent for masking pure tones

Back 53

Noise - Narrow Band

Front 54

not aperiodic
fundamental frequency is 60-60 Hz and a series of harmonics
sounds like humming
-useless in audiometric testing

Back 54

Sawtooth noise

Front 55

-regular repeating waveform
-components are harmonics of some fundamental frequency
-musical in quality and mathematically related

Back 55

Complex Periodic Sound

Front 56

lowest partial of a complex wave is

Back 56

almost always the fundamental frequency of a complex periodic sound
-study slide 12 of Acoustics II

Front 57

any single frequency component of a complex tone

Back 57

partial

Front 58

x axis (frequency)

Back 58

abscissa

Front 59

y axis (intensity/ dB)

Back 59

ordinate

Front 60

-illustration of the complex wave into individual parts of the whole
-usually shows discrete frequencies as part of a larger acoustic event
-frequency distribution

Back 60

spectrum

Front 61

whole number MULTIPLES of a fundamental frequency

Back 61

Harmonic

Front 62

first harmonic is the ____

Back 62

fundamental frequency

Front 63

Second harmonic is _____
Third harmonic is ______

Back 63

2 times the fundamental frequency (f sub zero X 2) (first overtone as well)
3 times the fundamental frequency

Front 64

not the fundamental frequency, the first one of these has a frequency which is 2 times the fundamental frequency or the second harmonic

Back 64

overtones

Front 65

If 125 Hz is the fundamental frequency, then ____ Hz would be the first overtone and the ____ would be the second overtone, etc.

Back 65

250, 375

Front 66

each successive _____ is multiplied by two

Back 66

octave series
Example:
200, 400, 800, 1600, 3200, ...
Study slide 33 in Acoustics II

Front 67

each successive _______ is an addition of the fundamental frequency

Back 67

harmonic series:
Example:
200, 400, 600, 800, 1000, 1200

Front 68

-system vibrates at one specific frequency - natural frequency
-free vibrator will absorb sound energy best when the energy source has a frequency which is the same of the vibrator

Back 68

free vibration

Front 69

-degree of damping occurs
-when enough energy is applied continuously to the vibrator
-makes up for the loss of energy through mechanical resistance

Back 69

Forced vibration

Front 70

-ratio of most intense sound possible tolerated by human ear
AND
-least intense sound pressure detected by the ear is

Back 70

100,000,000,000,000 : 1

Front 71

sound exerts ______ on objects it encounters

Back 71

pressure

Front 72

pressure increases as intensity _____

Back 72

increases and reverse is true -
pressure decreases as intensity decreases

Front 73

1+ 0 = 1
1+ 1 = 2
1+ 2 = 3
Where 1 is the numerical unit

Back 73

Interval Scale, intervals between successive values are equal and linear

Front 74

If 2 is numerical unit:
2 * 0 = 0
2* 1 = 2
2 * 2 = 4
2* 4 = 8

Back 74

Ratio scale, each product is twice the value of it's predecessor

Front 75

we can use 10 to the 14th power instead of

Back 75

100,000,000,000,000

Front 76

convert the ratio scale to an interval scale

Back 76

0-14, remove the bases, keep the exponents

Front 77

Moving from 10 to the 7th to 10 to the 8th is actually

Back 77

90,000,000
10,000,000 -> 100,000,000

Front 78

interval scale for human hearing is how many bels or decibels:

Back 78

14 bels or 140 decibels

Front 79

move from 20 to 30 decibels

Back 79

900 decibels

Front 80

dimensionless quantities

Back 80

ratios

Front 81

dB Intensity Level (IL) = 10 * Log I sub output/I sub reference point

Back 81

0 is output level
R is reference point
IL uses 10

Front 82

dB Sound Pressure Level (SPL) = 20 * Log P sub O/P sub R

Back 82

0 is output level
R is reference point
SPL uses 20

Front 83

Intensity is proportional to pressure ________

Back 83

squared

Front 84

Ratio of 2 sounds:
I output level = 10,000,000: I reference point = 1
then the IL is??

Back 84

70 watts (dB IL)
dB = 10 log 10 to the 7th/1
log of 10 to the 7th is 7
dB = 10 * 7

Front 85

Ratio of 2 sounds:
I output level = 10,000,000: I r = 1
then the SPL is??

Back 85

140 watts (dB SPL)
dB = 20 log 10 to the 7th/1
log of 10 to the 7th is 7
dB = 20 * 7

Front 86

The dB ______ is relative and not absolute

Back 86

scale

Front 87

threshold for starting point

Back 87

sound is the same as freezing water
by convention:
0 dB SPL = 20 μ Pa

Front 88

=force / unit area

Back 88

PRESSURE

Front 89

Smallest unit of sound pressure variation required to produce audible sound to healthy young ears

Back 89

.00002 or 20 μ Pa
μ = 1 millionth

Front 90

Frequency can be found by:

a dividing the frequency by one – f/1

b multiplying the frequency by the period – f x T

c dividing the period into one – 1/T

d dividing one into the period – T/1

Back 90

C

Front 91

1 bel =

Back 91

10 decibels