Exam 1 Basic Acoustics

Front 1

Definition of Sound

Back 1

A condition of disturbance of the particles of a medium which is propagated in the form of a wave outward in all directions from a vibrating body. This disturbance takes the form of displacement of the particles forward and backward from their positions of rest, in the direction of the propagation of the wave.

Front 2

Conditions for sound production

Back 2

1. Energy source (air from lungs)

2. Vibrator (vocal folds)

3. Transmitting medium (air)

4. Receiving mechanism (ears-auditory system)

Front 3

Definition of vibration

Back 3

back and forth movement of a body or object

Front 4

Facts about vibration

Back 4

- key factor in sound production

- all types of sound involve vibrations

- occurs when a body is disturbed by external force so that it moves back and forth around its original rest position

Front 5

For vibrations to occur, a body must have certain physical properties, which are...

Back 5

1. elasticity

2. inertia

3. small damping factor

Front 6

Types of vibration

Back 6

1. periodic

a. simple

b. complex

2. aperiodic

Front 7

Periodic Vibrations

Back 7

1. vibrations that occur in regular pattern so that they repeat themselves in equal (regular) intervals of time; motion of vibrating body (vibrator) occurs over and over again in the same manner

Front 8

2 types of periodic motion

Back 8

1. simple periodic motion (simple harmonic motion) - pure tones

2. complex periodic motion - complex tones (ex. some speech sound and musical tones)

Front 9

Pure tones

Back 9

1. sounds produced by a vibrating body that moves in a simple and periodic manner

2. produced mechanically using tuning forks or electronically generated

3. are used extensively for both measurement and calibration purposes in the acoustics/psychoacoustics lab

4. are also used to determine degree of hearing impairment in audiological testing in the hearing clinic

Front 10

What is an audiometer

Back 10

a fundamental diagnostic instrument for hearing tests; it generates pure tones via oscillator and controls several properties of pure tones: amplitude, frequency, period, and phase

Front 11

Aperiodic vibrations

Back 11

vibrations in a erratic or non-regular (non periodic) pattern; noise and some speech sounds (ex. /s/)

Front 12

All types of vibrations have certain basic properties in common...

Back 12

amplitude, frequency, period, and phase

Front 13

Amplitude

Back 13

- maximum displacement of a vibrator; distance that a vibrator moves during vibration

- the greater the distance of vibrator from rest position, the greater the amplitude

- determines physical characteristic of sound called intensity, and the perceptual aspect of sound known as loudness

- the greater the amplitude, the louder the tone

Front 14

spring-mass model

Back 14

the distance of mass from rest position at any instant in time is called its displacement; maximum displacement=amplitude of the vibration

Front 15

Hz =

Back 15

frequency

cycles per second

Front 16

There _______ a 1:1 ratio between Hz and pitch

Back 16

IS NOT

Front 17

Peak amplitude

Back 17

maximum momentary displacement; in sine waves, peak amplitude occur twice in 1 cycle

Front 18

peak-to-peak amplitude

Back 18

distance between maximum displacement points in both directions around rest position; in sine waves, peak-to-peak amplitude is twice the peak amplitude

Front 19

What is frequency?

Back 19

the number of complete vibrations made by a vibrator in a given unit of time; number of complete cycles of vibration that occur in one second

Front 20

Cycle

Back 20

the movement of a vibrator (or particle within a vibrator) from its position of rest to maximum displacement in one direction, back through its position of rest, to maximum displacement in the opposite direction, and back again to its position of rest

Front 21

Range of frequencies for human hearing

Back 21

20-20,000 Hz

Front 22

Most sensitive range of frequencies to humans

Back 22

1,000-3,000

Front 23

The higher the frequency of the tone...the _______the perceived pitch

Back 23

higher

Front 24

Period

Back 24

- amount of time necessary for completion of one cycle of vibration; the number of seconds for one cycle to occur

- period is reciprocal of frequency of a vibrator

T=1/f

(ex. period of an 8,000 Hz tone is 1/8,000 sec or .0001sec; if 8,000 Hz occur in 1 sec, then it takes 1/8,000 sec. to complete 1 cycle

- frequency is the reciprocal of period

(ex. if the period of a vibration is .01 sec, its frequency is 100 Hz (1/.01))

Front 25

Phase

Back 25

-the portion of a cycle through which a vibrator has passed up to a given instant in time; that portion of a cycle that has elapsed at any instant in time relative to some arbitrary starting point

-usually measured in degrees of a circle

-number of degrees within one completed cycle of vibration = 360

Front 26

In-phase

Back 26

two waves represented by sine curves are said to by "in-phase" at any given point (instant in time) when their degree of advancement from an arbitrary zero point is equal

Front 27

Out-of-phase

Back 27

a condition in which a phase difference exists between vibrating sources; thus, both vibrators do not assume identical phase angles at every instant in time

Front 28

Waves traveling through a medium of air are called...

Back 28

sound waves

Front 29

All kinds of waves involve a....

Back 29

disturbance

-i.e. a back and forth movement, a vibration, caused by various disturbance-producing mechanisms. Differences between different wave types involve differences in vibrator, source of energy, and transmitting medium

Front 30

Sound waves are_________ waves

Back 30

Longitudinal

Front 31

Sound cannot be produced without a _________ between source of vibration and ear

Back 31

medium

(sound cannot be conducted in the absence of matter (sound does NOT travel through a vacuum))

Front 32

The most common medium through which sound is transmitted is ____________

Back 32

air

Front 33

Air has ___________ and_____________ and therefore can serve as a medium for transmission of waves

Back 33

-mass

-elasticity

Front 34

Air is composed of minute particles called ______________

Back 34

molecules

(there are more than 400 billion molecules in every cubic inch of air)

Front 35

Each molecule is assumed to have some average stable position called its___________________

Back 35

rest position

Front 36

Sound waves _______________ transverse waves

Back 36

are NOT

Front 37

The movement of molecules closer together in air produces a _____________________

Back 37

wave of compression (wave of condensation)

Front 38

Each wave of compression is followed by _______________________

Back 38

a wave of rarefaction (wave of expansion)

Front 39

In a state of compression there is ___________ of pressure

In a state of rarefaction there is _____________ of pressure

Back 39

- increase

- decrease

Front 40

What is a sound wave?

Back 40

the movement of a disturbance though a material medium such as air without permanent displacement of molecules

Front 41

Speed of sound wave in air is approximately...

Back 41

340 meters (34,000 cm, 1130ft) per second

Front 42

Sine curves are used to represent...

Back 42

particle pressure, particle velocity, or particle displacement as well as the sound wave itself

Front 43

pressure equals ________ when molecules are in rest position

Back 43

0

Front 44

Particle velocity increases as it approaches middle of swing and it is at its maximum value when it is in its _______ position

Back 44

rest

Front 45

pressure is at its greatest at _______ velocity;

pressure is at its least at its _______ velocity

Back 45

- lowest

- greatest

Front 46

Particle displacement

Back 46

degree of displacement of a particle to right (above line) or left (below line) as it moves away from, or toward, source of sound

Front 47

Sound is not transmitted ______________

Back 47

instantaneously

(it takes time for a sound wave to travel from its source to listener)

Front 48

Velocity

Back 48

distance which a sound wave will be transmitted (propagated) through a given medium in a single unit of time

(velocity is measured in meters, cm, or ft per second)

Front 49

Factors that affect velocity of sound

Back 49

- elasticity

- density

- temperature

Front 50

Elasticity

Back 50

resistance to distortion offered by medium, it is the most important factor in determination of velocity

Front 51

the greater the elasticity of a medium, the _________ transmission of wave

Back 51

more rapid

(i.e. the greater the velocity of sound)

Front 52

Density

Back 52

mass per unit of volume; it is proportional to the number of molecules in a given volume of air

Front 53

The greater the density of a medium, the __________ the speed of wave being transmitted

Back 53

slower

Front 54

the more molecules in a given volume of air (the greater the density) the ____________ it will take the wave to be transmitted through the medium

Back 54

longer

Front 55

velocity of a sound wave increases when elasticity of medium ____________ and when density _____________

Back 55

- increases

- decreases

Front 56

velocity formula

Back 56

velocity = elasticity / density

velocity = wavelength x frequency

Front 57

an increase in velocity of sound occurs with _________ in temperature of medium

Back 57

an increase

Front 58

when temperature increases, molecules .......

Back 58

spread farther apart

Front 59

sounds travel ________ through steel than air because....

Back 59

faster

- steel has more elasticity

Front 60

Normally, all sounds, regardless of pitch or loudness, travel through air...

Back 60

at the same velocity

Front 61

Wavelength

Back 61

distance between points of identical phase in 2 adjacent cycles of a wave; distance between successive compressions (or rarefactions) in space

Front 62

wavelength formula

Back 62

wavelength = velocity / frequency

Front 63

as frequency increases, wavelength ___________

Back 63

decreases (gets shorter)

Front 64

the greater the velocity, the ____________ the wavelength

Back 64

- longer

Front 65

frequency formula

Back 65

frequency = velocity / wavelength

Front 66

frequency of a sound wave (does/does not) change in passing though different transmitting media; but velocity of sound wave (will/will not) vary with different transmitting media

Back 66

- does not

- will

Front 67

Types of interference in the transmission of sound waves

Back 67

reflection, absorption, refraction

Front 68

when a sound wave impinges on any surface, result will be either ____________ or ____________ of wave's energy

Back 68

- reflection

- absorption

Front 69

Reflection

Back 69

is turning back of a wave upon itself when it encounters an abrupt change in nature of medium in which it is traveling

Front 70

2 types of reflection of sound waves

Back 70

1. diffuse reflection

2. regular reflection

Front 71

Diffuse reflection

Back 71

- results when reflecting surface is rough

- only a small portion of sound wave energy is reflected from a rough surface

Front 72

regular reflection

Back 72

- results when sound wave is reflected off a smooth surface

- much or all of sound wave energy is reflected from a smooth surface

Front 73

percentage of energy of a sound wave which will be reflected depends on the ___________

Back 73

-surface

(solid surfaces=up to 100% of sound wave energy;thus giving maximum reflection)

(porous surfaces=minimum reflection; sometimes approaching 0%)

Front 74

Echoes

Back 74

brief periods of reflection which are not sustained

Front 75

Reverberation

Back 75

continual or prolonged reflection

- may produce blurred sound effects, unintelligible speech, or unintelligible music

Front 76

Absorption

Back 76

reduction in reflection of energy of sound waves by dissipation of all or some of sound energy

Front 77

absorption coefficient

Back 77

effectiveness of a given material in absorbing sound energy; percentage of energy that is absorbed, as compared to the total energy available in sound wave

ex. if a material absorbs 60% of incident energy, and reflects 40%, then its absorption coefficient is .6

Front 78

In general, absorption factor is __________ for lower frequencies

Back 78

lower

Front 79

When does refraction of a sound wave occur?

Back 79

when determinants of velocity (elasticity, density, and temperature in a medium) vary

Front 80

Plane wave

Back 80

sound waves tend to move outward from source of sound in the form of a sphere, but after about 6 feet from source, wavefront approaches a plane surface, resulting in a plane wave

Front 81

Refraction (deflection)

Back 81

phenomenon of bending of sound waves form their path of propagation

Front 82

Most sounds in our environment are ___________

Back 82

complex

- vibrating sources not moving in a simple back-and-forth motion

Front 83

2 types of complex vibrations

Back 83

- complex periodic vibration

- complex aperiodic vibration

Front 84

complex periodic vibration

Back 84

a complex vibration that repeats itself over and over again in time; vowels are produced by complex periodic vibration

Front 85

complex aperiodic vibration

Back 85

a complex vibration that does not produce repeatable patterns of vibration; fricatives are produced by complex aperiodic vibration

Front 86

"component" of a complex wave

Back 86

each of the simple pure tones included in complex wave

Front 87

When has the spectrum of a complex wave been described?

Back 87

when amplitude and frequency of complex wave's sinusoidal components have been specified

Front 88

what is a spectrum?

Back 88

graphic representation of frequencies and relative amplitudes of components of a complex wave; graphic representation of the waveform

- vertical axis=amplitude

- horizontal axis= frequency

Front 89

Fourier analysis

Back 89

analysis of complex periodic waves into their sinusoidal components; shows that sum of many sinusoidal waves is equivalent to a wave with a non-sinusoidal (complex) shape

ex. a complex wave

Front 90

2 general types of spectra

Back 90

- continuous

- discrete

Front 91

Continuous spectrum

Back 91

shows energy spread throughout entire frequency range; used to represent aperiodic signals

Front 92

Discrete spectrum

Back 92

shows energy at discrete points in frequency range; used to graphically represent periodic waves

Front 93

spectrum analysis (harmonic analysis)

Back 93

method of analyzing complex waves into their component parts

Front 94

Waveform

Back 94

plot that shows amplitude of a sound at each instant in time

- vertical axis=amplitude

- horizontal axis=time (in seconds)

Front 95

fundamental frequency

Back 95

pure tone component with lowest frequency

Front 96

harmonics

Back 96

other higher component frequencies in complex tone; they are integral (whole-number) multiples of fundamental

Front 97

timbre

Back 97

quality of musical tones; derived from varying amplitude patterns of harmonics (amplitude of harmonic varies in relative intensity from one instrument to another)

-number, distribution, and relative amplitude of harmonics determine quality/timbre

Front 98

Partial tones (partials)

Back 98

component pure tones of a complex periodic signal

Front 99

Overtones

Back 99

partials with frequencies higher than that of fundamental

Front 100

In general, the more harmonics a tone contains, the _________ and __________ it sounds

Back 100

fuller and richer

Front 101

3 factors that influence the shape of a complex wave

Back 101

1. frequency

2. amplitude

3. phase

Front 102

All harmonics are ________________

Not all overtones are ___________

Back 102

- overtones

- harmonics

Front 103

cross hearing

Back 103

when test signal is heard in ear not being tested (white noise or narrowband noise, a complex aperiodic vibration, are used to eliminate this)

Front 104

Resonance

Back 104

the phenomenon whereby a body, which has a natural tendency to vibrate at a certain frequency (its resonant frequency) will exhibit greater amplitudes of vibration when set into vibration by another body whose frequency of vibration is identical, or similar, to the natural frequency of the first body; the closer the frequency of the driving system to the natural frequency of the resonator, the greater the amplitude of the vibrations

Front 105

it is important to note that a resonator gives no tone unless...

Back 105

impulses are received from some other vibrator which, in turn, is activated by a generator

Front 106

The principle of resonance is applied in 3 different ways

Back 106

1. sympathetic vibration

2. "sounding-board" effect

3. cavity resonance

Front 107

Sympathetic Vibration

Back 107

if two tuning forks of equal frequency are placed near each other, and one fork is struck and if its vibration is stopped, a sound will be heard from the second, unstuck tuning fork

Front 108

Sounding Board Effect

Back 108

- a vibrating body (ex. a tuning fork) is placed in direct contact with some large resilient surface

- ex. waves of a oscillating tuning fork are of low amplitude; they only disturb the air a little. But if a stem of fork is placed on a table or some other resilient surface of considerable dimensions, it can set a second tuning fork into vibration, and these vibrations will involve disturbance of the air particles over a larger area

Front 109

Cavity Resonance

Back 109

- a vibrating tuning fork held in the hand will give out a barely audible tone

- but if it is held over open end of a tube of proper length, or over mouth of a jar or bottle of proper size, the resulting tone will be quite strong

- tube or bottle or jar acts as a resonator (waves from fork are added to those from body of air in resonator, thus providing a resultant wave of much greater amplitude than original waves from tuning fork

Front 110

Principle of Frequency Response Curve

Back 110

- if a vibrating tuning fork is placed over one end of a tube that has two open ends (but one is immersed in water) by moving the tube up and down, a point will be reached where maximum amplitude of sound from fork will be heard

Front 111

Resonant (natural) frequency

Back 111

- point of maximum amplitude of the sound

Front 112

Frequency response curve (resonance curve)

Back 112

-spectrum of a complex sound also provides a description of the natural frequencies of vibration of the sound

- frequencies to which a resonator will respond

- shows not only the component (pure tone) frequencies of the complex wave, but also the frequencies at which the wave resonates

- graphic representation

Front 113

damped resonator

Back 113

can be set into vibration by a wide range of frequencies

- damped resonators are described by flat frequency response curves

- sound source whose vibrations die away quickly

- ex. sounding board of a piano and the body of a violin

Front 114

undamped resonator

Back 114

requires a long time for its vibrations to build up and die away; undamped resonators can be set into vibration by only a limited range of frequencies

- ex. tuning forks

Front 115

bandwidth

Back 115

- the range of frequencies to which a resonator will resonate

- effective frequency range of a resonator

Front 116

cavity (acoustical) resonance is analogous to...

Back 116

the air in the vocal tract

the air in the external auditory meatus

Front 117

Acoustic filter

Back 117

a resonator used to transmit or pass on sound

- when a resonator behaves in this manner of making some vibrating forks and not making others audible

- selective with respect to frequency; it transmits some frequencies with greater efficiency than other frequencies

Front 118

a tube with uniform cross-sectional dimensions throughout its length has______________________________________; the values of these resonant frequencies depend on ___________ of tube

Back 118

- regularly spaced resonant frequencies

- length

Front 119

For a tube that is closed at one end and open at the other end, the lowest resonant frequency (natural frequency) is equal to the frequency of a sound wave whose wavelength is .....

Back 119

4 times the length of the tube

Front 120

Coupling

Back 120

occurs when two or more resonators, each capable of resonance, are joined together; when any part of the system vibrates, force will be exerted on the other part(s) of the system, and it (they) will also vibrate

Front 121

loosely coupled system

Back 121

one in which the force that one part of the system exerts on the other part(s) is small

Front 122

tightly coupled system

Back 122

one in which the force that one part of the system exerts on the other part(s) is great

Front 123

Sound frequency is determined by...

Back 123

number of complete cycles per second of sound wave

Front 124

range of audible frequencies that human ear can perceive

Back 124

20-20,000 Hz

Front 125

ultrasonic sounds

Back 125

sounds above 20,000 Hz (in medicine and industry)

Front 126

subsonic sounds

Back 126

sound below human audibility (below 20 Hz)

- often felt via their vibration

Front 127

frequencies important in speech signal

Back 127

100-8,000 Hz

Front 128

There is a very strong relationship between speech production and______________

Back 128

speech perception

Front 129

Doppler Effect

Back 129

-stationary listener & moving sound source (vice versa)

- train moving toward stationary observer the pitch seems to get higher because more sound waves per second reach listener's ear as train gets closer

- train moves away from stationary listener, pitch is perceived as getting lower because fewer sound waves are reaching observer's ear per second

- FREQUENCY OF SOUND REMAINS CONSTANT

- CHANGE IN PERCEIVED PITCH

Front 130

Sound intensity

Back 130

physical measurement related to perception of loudness of a sound; the greater the intensity of a sound, the louder is its perception

- rate at which energy is given off by a sound source, or energy with which a sound wave strikes an object

Front 131

Energy

Back 131

capacity for doing work (force X distance)

Front 132

amount of energy produced depends on what 2 factors?

Back 132

-amplitude

- frequency

Front 133

intensity of a sound is most often measured in _________ and ___________

Back 133

-power

-pressure

Front 134

Pressure

Back 134

force per unit area

- measured in dynes/cm 2 or microbar or Pascal (Pa)

- created when a force is distributed over an area

- .0002 dyne/cm 2 or Pa

Front 135

Pascal

Back 135

most current unit of measurement for sound pressure

- equivalent t dyne/cm 2 or microbar

Front 136

Power

Back 136

amount of work done per unit of time (or rate at which energy is used)

- expressed in watts

Front 137

Intensity is usually measured in....

Back 137

sound pressure

- but it can also be measured in power

Front 138

The energy of individual speech sounds is very small or large?

Back 138

-small

- estimated it would take 4 million people all talking at once to light a single 40-watt light bulb

- however, the human ear is capable of hearing a very wide range of sound intensities

Front 139

Loudest sound that can be heard without pain ________ dynes/cm 2

Softest sound that can be heard ______ dynes/cm 2

Back 139

- 2000 (10 million times the softest intensity)

- .0002

Front 140

Clinical practice intensity of sound is expressed as a ________ rather than as an absolute magnitude

Back 140

ratio

Front 141

Linear Scale

Back 141

all units on the scale are the same size (10 to 11 inches on a ruler is exactly the same distance as 50 to 51 inches)

- inches and pounds are linear scales

Front 142

Logarithmic scales

Back 142

each unit in the scale is larger than the preceding unit

- in the numbers 1, 2, 4, 8, 16, 32, 64 the distance between the numbers is not equal; distance between units gets progressively larger

Front 143

Decibel (dB) scale

Back 143

a logarithmic scale (not linear)

- cannot be added and subtracted in a conventional manner

- 1 to 2 dB is smaller than from 2 to 3 dB

Front 144

Doubling of sound pressure involves the addition of _____ DB

Back 144

6

Front 145

Decibel scale is a ________ scale not an absolute scale

Back 145

relative (ratio)

(it measures intensity of sound in comparison to some other sound)

Front 146

Absolute Scales

Back 146

- zero point of scale represents absence of what is being measured

- a true zero point

- no negative numbers

( ex. 0 inches represents absence of distance; something cannot be -5 inches long)

Front 147

Relative Scale

Back 147

- no true zero point

- zero value is arbitrarily and unanimously selected by users of the scale

- zero point does not mean absence of measure, but rather the base of the scale

(ex.decibel and temperature)

Front 148

Logarithmic scale uses _________ of some constant number

Back 148

exponents

Front 149

constant number =

Back 149

base

Front 150

Logarithm

Back 150

value to which a base must be raised to equal desired number

- exponent

Front 151

Inverse square law

Back 151

describes relationship of intensity and distance: intensity varies inversely as the square of the distance from the sound source