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Physics: Acoustics > Exam II > Flashcards

Exam II Flashcards

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1
Q

Complex Vibration:

A

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

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2
Q

Fourier Theorem:

A

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

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3
Q

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

A
  1. Aperiodic Vibration

2. Periodic Vibration

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4
Q

Aperiodic Vibration:

A

vibration without a repeating pattern in time

Frequencies do not have a common factor

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5
Q

Periodic Vibration:

A

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

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6
Q

Periodic vibration has:
1.
2.

A
  1. Fundamental frequency and a fundamental period

2. Harmonics

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7
Q

A Periodic frequency is composed of _________ that __________.

A

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)

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8
Q

Fundamental Frequency:

A

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.

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9
Q

frequency = _______/________

A 
Frequency = cycles/second = Hz
F= 1/T
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10
Q

period = _________/_________

A

Period = seconds/cycle = seconds

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11
Q

Waveform Synthesis:

A

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

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12
Q

Waveform Analysis:

A

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

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13
Q

Compression

A

bunching of particles causing increased density (in a wave)

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14
Q

Rarefaction

A

spreading of particles causing decreased density (in a wave)

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15
Q

Sound Intensity

A

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

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16
Q

sound intensity = ____________/____________

A

sound intensity = power/area w/m^2

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17
Q

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

A

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

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18
Q

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

A

Increases

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19
Q

If sound source is moving away from listener, frequency__________.

A

Decreases

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20
Q

The Doppler Effect

A

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

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21
Q

Frequency depends only on __________, not _______.

A

Frequency depends only on speed, not distance.

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22
Q

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

A

Speed

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

23
Q

Sound Pressure vs Sound Intensity

A

Sound Pressure: how compressed or rarefied particles are

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

24
Q

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

A

Sound absorption by the medium and surrounding boundaries.

25
Q

Sound absorption is the result of _________.

A

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

26
Q

Internal absorption

A

absorption by the medium.

the dominant factor in sound energy dissipation in open spaces and large sports arenas

27
Q

External absorption

A

absorption by space boundaries

the dominant factor in sound decrease in enclosed spaces such as auditoriums, living rooms, classrooms.

28
Q

Absorption Coefficient

A

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

29
Q

Reflection

A

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

30
Q

Refraction

A

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

31
Q

Atmospheric Absorption:

The amount by which air absorbs sound depends on _______.

A

Frequency, relative humidity, and other factors.

32
Q

Dispersion

A

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

33
Q

Incident Wave

A

Original incoming sound wave

34
Q

Angle of incidence

A

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

35
Q

Attenuation

A

a decrease in the magnitude of a signal

36
Q

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

A

bend toward the normal line

37
Q

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

A

away from the normal line

38
Q

Angle of reflection

A

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

39
Q

Law of reflection:

A

Angle of reflection EQUALS Angle of incidence

40
Q

Reverberation Time

A

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

41
Q

Total Internal Reflection

A

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

42
Q

When does total internal reflection occur?

A

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)

43
Q

Critical Angle of Incidence

A

smallest angle at which total internal reflection can occur

44
Q

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

A

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

45
Q

Reverberation

A

The reflected sound energy within an enclosed space.

46
Q

Sound Diffraction

A

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

47
Q

Diffraction increases as wavelength _____________.

A

increases.

48
Q

Diffraction increases as frequency____________.

A

Decreases (waves spread out and bend more)

49
Q

Shock Wave

A

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.

50
Q

Sonic Boom

A

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

51
Q

Minimum sound intensity heard by human ear:

A

20 uPa

1.0x10^-12 W/m^2

52
Q

Threshold of pain

A
  1. 0x10^7 uPa

1. 0 W/m^2

53
Q

Intensity Level Decibel (dB IL)

A

Standard means of measuring the amplitude of an acoustic signal

Physics: Acoustics (1 decks)

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