Exam II

Question 1

Complex Vibration:

Answer 1

The sum of two or more simple vibrations. Simple vibrations that make up a complex vibration are called frequency components.

Question 2

Fourier Theorem:

Answer 2

Any complex oscillatory (vibratory) motion is the sum of various sinusoidal motions of varying amplitude, frequency, and phase.

Question 3

Complex vibration can be divided into two basic classes of back and forth motion:
1.
2.

Answer 3

1. Aperiodic Vibration

2. Periodic Vibration

Question 4

Aperiodic Vibration:

Answer 4

vibration without a repeating pattern in time

Frequencies do not have a common factor

Question 5

Periodic Vibration:

Answer 5

vibration in which an object returns to the same point in space periodically (at equal periods of time) during the motion

Question 6

Periodic vibration has:
1.
2.

Answer 6

1. Fundamental frequency and a fundamental period

2. Harmonics

Question 7

A Periodic frequency is composed of _________ that __________.

Answer 7

composed of frequencies that are integer multiples of a fundamental frequency, even if that fundamental frequency is not a part of the vibration (aka missing fundamental)

Question 8

Fundamental Frequency:

Answer 8

The greatest common factor of all the harmonic frequencies (aka overtones) in the complex waveform.

Ex: waveform made up of 1500Hz, 1800Hz, 2400Hz, 2700Hz. Fund. frequency is 300Hz- GCF.

This is an example of a missing fundamental, because it does not start at 300. 5th, 6th, 8th, and 9th harmonics are given.

Question 9

frequency = _______/________

Answer 9

Frequency = cycles/second = Hz
F= 1/T

Question 10

period = _________/_________

Answer 10

Period = seconds/cycle = seconds

Question 11

Waveform Synthesis:

Answer 11

The process of combining several individual sinusoidal motions into a complex waveform.

Question 12

Waveform Analysis:

Answer 12

The process of breaking down a complex waveform into individual sinusoidal waves.

Question 13

Compression

Answer 13

bunching of particles causing increased density (in a wave)

Question 14

Rarefaction

Answer 14

spreading of particles causing decreased density (in a wave)

Question 15

Sound Intensity

Answer 15

the amount of sound power that travels through a specific area of the wave front surface

Question 16

sound intensity = ____________/____________

Answer 16

sound intensity = power/area w/m^2

Question 17

10 dB = ______x Louder
20dB = ______x Louder
30dB = ______x Louder

Answer 17

10 dB = 2x Louder
20dB = 4x Louder
30dB = 8x Louder

Question 18

If sound source is moving toward listener, or listener moves toward sound source, frequency________.

Answer 18

Increases

Question 19

If sound source is moving away from listener, frequency__________.

Answer 19

Decreases

Question 20

The Doppler Effect

Answer 20

a shift in the frequency of a sound wave resulting from the movement of a sound source, the movement of a listener, changes in the medium, or a combination of these factors

Question 21

Frequency depends only on __________, not _______.

Answer 21

Frequency depends only on speed, not distance.

Question 22

Which property of a wave does not change due to the Doppler Effect?

Answer 22

Speed

The speed of a wave is determined by the properties of the medium, not the speed of the source or the observer.

Question 23

Sound Pressure vs Sound Intensity

Answer 23

Sound Pressure: how compressed or rarefied particles are

Sound Intensity = How much sound power is transferred from the sound source to the surrounding area

Question 24

A sound wave propagating through a medium will ultimately lose all of its energy because of _______.

Answer 24

Sound absorption by the medium and surrounding boundaries.

Question 25

Sound absorption is the result of _________.

Answer 25

Internal friction within the medium which converts sound energy into heat as sound passes through a medium.

Question 26

Internal absorption

Answer 26

absorption by the medium. | the dominant factor in sound energy dissipation in open spaces and large sports arenas

Question 27

External absorption

Answer 27

absorption by space boundaries | the dominant factor in sound decrease in enclosed spaces such as auditoriums, living rooms, classrooms.

Question 28

Absorption Coefficient

Answer 28

The ability of the medium and its boundaries to absorb the energy of sound waves.

Question 29

Reflection

Answer 29

when a sound wave strikes the surface of a space boundary, part of its energy is absorbed by the boundary medium and the remaining energy is reflected back to space

Question 30

Refraction

Answer 30

when a sound wave bends (changes direction) after entering a medium with a different density and stiffness.

Question 31

Atmospheric Absorption: | The amount by which air absorbs sound depends on _______.

Answer 31

Frequency, relative humidity, and other factors.

Question 32

Dispersion

Answer 32

If a sound wave hits a smooth, flat surface, all of the waves will reflect in the same direction. If a sound wave hits a curved and rough surface, the sound energy may be reflected in different directions--- this is called dispersion

Question 33

Incident Wave

Answer 33

Original incoming sound wave

Question 34

Angle of incidence

Answer 34

The angle at which the incident wave approaches the boundary compared to the normal line.

Question 35

Attenuation

Answer 35

a decrease in the magnitude of a signal

Question 36

When waves enter a medium of lesser speed (fast to slow) they bend _______ the normal line.

Answer 36

bend toward the normal line

Question 37

When waves enter a medium of faster speed (slow to fast) they bend _______the normal line.

Answer 37

away from the normal line

Question 38

Angle of reflection

Answer 38

angle at which the reflected ray bounces off the wall and into the original medium

Question 39

Law of reflection:

Answer 39

Angle of reflection EQUALS Angle of incidence

Question 40

Reverberation Time

Answer 40

The time required for the sound intensity to decrease to 1 millionth of its original magnitude. Equivalent to sound intensity decreasing by 60 dB.

Question 41

Total Internal Reflection

Answer 41

when 100% of the sound energy reaching a boundary is reflected back into the original medium;

Question 42

When does total internal reflection occur?

Answer 42

Occurs when a sound wave enters a boundary with a denser medium and is traveling at a sufficiently large angle (greater than 90degrees past the normal line)

Question 43

Critical Angle of Incidence

Answer 43

smallest angle at which total internal reflection can occur

Question 44

Lower absorption coefficient (a) = __________ reflectivity (B)

Answer 44

Lower absorption coefficient (a) = HIGHER reflectivity (B)

Question 45

Reverberation

Answer 45

The reflected sound energy within an enclosed space.

Question 46

Sound Diffraction

Answer 46

the phenomenon of sound waves bending around objects and through openings in boundaries.

Question 47

Diffraction increases as wavelength _____________.

Answer 47

increases.

Question 48

Diffraction increases as frequency____________.

Answer 48

Decreases (waves spread out and bend more)

Question 49

Shock Wave

Answer 49

When a moving object travels at or faster than the speed of sound, it compresses the medium in front of it and takes the compressed waveform with it.

Question 50

Sonic Boom

Answer 50

Noise created by a shock wave. Not heard until it reaches the listener.

Question 51

Minimum sound intensity heard by human ear:

Answer 51

20 uPa | 1.0x10^-12 W/m^2

Question 52

Threshold of pain

Answer 52

2. 0x10^7 uPa | 1. 0 W/m^2

Question 53

Intensity Level Decibel (dB IL)

Answer 53

Standard means of measuring the amplitude of an acoustic signal