2. Acoustics
The science of sound, including its
production, propagation and effects
The objective study of the physical behavior
of sound in an enclosed space
Sound
A wave motion consisting of a series of
condensations and rarefactions in an elastic
medium produced by a vibrating body
5. AUDIBLE FREQUENCY RANGE
Infrasonic/Subsonic
frequencies below the audible range
Ultrasonic/Supersonic
frequencies above the audible range
Audible Range: 20 Hz– 20kHz
7. General Interpretations of
Sound
1. Physical phenomenon consisting of
wave motion in a transmitting
medium (objective)
2. Sensation due to outside simulation
(subjective)
9. Physical Properties of Sound
1. Amplitude – magnitude of the
vibration (pressure, current, voltage)
2. Period – time it takes to complete a
vibration/cycle
3. Frequency – number of vibrations /
cycle per unit time
10. Physical Properties of Sound
4. Wavelength – physical length of a
vibration
5. Velocity of Propagation
Vsound << VRF
(344 m/sec << 3 x 108 m/sec)
13. Velocity of Sound
Gases
Where:
k = specific heat ratio = hsp/hsv
hsp = specific heat at constant pressure
hsv = specific heat at constant volume
p = gas pressure, dynes/cm2
d = density, g/cm3
17. Velocity of Sounds
Notes
Sounds travel more slowly in gases than in
liquids, and more slowly in liquids than in
solids.
Sounds travels slower with an increased
altitude (elevation if you are on solid earth),
primarily as a result and humidity changes.
18. QUESTIONS
1. Which best describes the sound wave?
a. It may be longitudinal
b. It is always transverse
c. It is always longitudinal
d. All of the above
19. 2. Which of the following cannot travel
through a vacuum?
a. Electromagnetic wave
b. Radio wave
c. Sound wave
d. Light wave
20. 3. Through which medium does sound
travel fastest?
a. Air
b. Water
c. Steel
d. Mercury
21. 4. Speed that is faster than that of
sound.
a. Ultrasonic
b. Supersonic
c. Subsonic
d. Transonic
22. 5. What is the speed of sound in air at
20°C?
a. 1087 ft/s
b. 1100 ft/s
c. 1126 ft/s
d. 200 ft/s
23. 6. Calculate a half wavelength sound
for sound of 16000 Hz
a. 35 ft
b. 10 ft
c. 0.035 ft
d. 100 ft
24. 7. The lowest frequency that a human
ear can hear is
a. 5 Hz
b. 20 Hz
c. 30 Hz
d. 20 kHz
25. 8. Sound that vibrates at frequency too
high for the human ear to hear (over 20
kHz)
a. Subsonic
b. Ultrasonic
c. Transonic
d. Stereo
26. 9. What is the speed of sound in a material
having a density of 1000 kg/cu.m. and
Young’s modulus of elasticity of 2.3 x 10exp
9 N/sq.m.?
a. 1517 m/sec
b. 1571 m/sec
c. 1715 m/sec
d. 1751 m/sec
27. 10. In acoustics, the volume velocity
component is a function of the _____ of the
material.
a. density
b. volume
c. diameter
d. Young’s modulus
28. 11. A sound intensity that could cause
painful sensation to the human ear.
a. threshold of sense
b. threshold of pain
c. hearing threshold
d. sensation intensity
31. Possibilities when a
Propagated Sound is
Obstructed (3)
Sound is Reflected
Echo
Becomes apparent to the listener only when the
distance from the source and the reflecting medium is
great and the difference between the original and
reflected sound is greater or equal to 1/17 of a second.
Flutter
Brought about by a series of reflections between two
parallel surfaces resulting to prolongation of sound
Creates listening fatigue
Interference
Reflection caused by two parallel surfaces, producing
standing waves
32. Possibilities when a
Propagated Sound is
Obstructed
Sound is absorbed
Conversion of sound energy to heat energy
Onward transmission through
obstruction
34. Physiological Characteristics
of Wave Motion (3)
Pitch
Number of cycles a wave goes through in a
definite interval
The higher the frequency, the higher the
pitch
Mel – unit of pitch
1000 mels – pitch of 1000Hz tone at 40dB
Octave – pitch interval 2:1; frequency is twice
the given tone
35. Physiological Characteristics
of Wave Motion (3)
Tone
Timbre quality of sound
Pure Tone – a sound composed of only one
frequency in which the sound pressure varies
sinusoidally with time.
Musical Sound – composed of the
fundamental frequency and its harmonics
36. Physiological Characteristics
of Wave Motion (3)
Loudness
Fluctuation of air pressure created by sound waves
Observer’s auditory impression of the strength of a
sound and is associated with the rate at which
energy is transmitted to the ear.
Depends on the amplitude of the sound
Loudness Level – measured by the sound level of a
standard pure tone or specified frequency which is
assessed by normal observers as being equally loud
37. PHON
Phon is the unit of loudness level
when:
The standard pure tone is produced by a
sensibly plane sinusoidal progressive
sound wave coming from directly in front of
the observer and having the frequency of
1kHz
The sound pressure level in the free
progressive wave is expressed in dB above
2 x 10-5 N/m2
38. SONE
Sone is the unit of loudness of an
individual listener.
Phon = 40 + 10 log2 sone
39. Sound Levels
Sound Pressure (P) and
Sound Pressure Level (SPL)
Sound Pressure
The alternating component of the pressure at
a particular point in a sound field
Expressed in N/m2 or Pa
40. Sound Levels
Sound Pressure Level
Equal to 20 times the logarithm to the base 10
of the ratio of the RMS sound pressure to the
reference sound pressure
SPL = 20 log (P/Po)
Where:
P = rms sound pressure
Po = reference sound pressure
Po = 2 x 10-5 N/m2 or Pa or 2 x 10-4
dynes/cm2
Po = 0.0002 μbar or 2.089 lb/ft2
42. Sound Pressure Levels
Sound Pressure Level (SPL) at any unit of
pressure in dB
SPL = 20log(P+N)
Where:
PN = rms sound pressure expressed in any of
pressure in dB
N = SPL constant corresponding to the unit
at which sound pressure is expressed
45. Sound Levels
Sound Intensity (I) and
Sound Intensity Level (SIL)
Sound Intensity
Defined as the acoustic power per unit area
The basic units are W/m2 or W/cm2
The average rate of transmission of sound
energy through a cross-sectional area of 1
m2 at right angles to a particular direction.
50. Sound Levels
Sound Intensity
I = ρ2 / d v
Where: d – density of the medium (kg/m3)
v – velocity of sound in medium (m/sec)
ρ – rms pressure in Pa (N/m2)
53. Sound Levels
Sound Power (W) and
Sound Power Level (PWL)
Sound Power (W)
The total energy radiated per unit time.
54. Sound Levels
Sound Power Level (PWL)
Where:
W = sound power , W
Wo = reference sound power
Wo = 10-12 w
55. 12. The frequency interval between two
sounds whose frequency ratio is 2.
a. Octave
b. Half octave
c. Third-octave
d. Decade
56. 13. A 16 KHz sound is how many octaves
higher than a 500 Hz sound
a. 2
b. 5
c. 4
d. 8
57. 14. Sound waves composed of but one
frequency is a/an
a. Infra sound
b. Pure tone
c. Structure borne
d. Residual sound
58. 15. Sound wave has two main
characteristics which are
a. Highness and loudness
b. Tone and loudness
c. Pitch and loudness
d. Rarefactions and compressions
59. 16. _____ is the sound power measured over
the area upon which is received.
a. Sound pressure
b. Sound energy
c. Sound intensity
d. Sound pressure level
60. 17. A measure of the intensity of sound in
comparison to another sound intensity
a. Phon
b. Decibel
c. Pascal
d. Watts
61. 18. Calculate the sound intensity level in
dB of a sound whose intensity is 0.007
W/m2.
a. 95 dB
b. 91 dB
c. 98 dB
d. 101 dB
62. 19. What is the sound pressure level for a
given sound whose RMS pressure is
200 N/m2?
a. 200 dB
b. 20 dB
c. 140 dB
d. 14 dB
63. 20. The amplitude of sound waves, the
maximum displacement of each air particle,
is the property which perceive as _____ of a
sound
a. Pitch
b. Intensity
c. Loudness
d. Harmonics
64. 21. If the sound source radiates 1 watt, what
is its sound power level?
a. 0 dB
b. 60 dB
c. 120 dB
d. 240 dB
65. 22. If a note has a fundamental frequency of
100Hz, what is its 5th octave?
a. 6400 Hz
b. 3200 Hz
c. 500 Hz
d. 1600 Hz
66. 23. What is the sound intensity for an RMS
pressure of 200 Pascal?
a. 90 W/m2
b. 98 W/m2
c. 108 W/m2
d. 88 W/m2
67. 24. The sound pressure level is increased by
_____ dB if the pressure is doubled.
a. 3
b. 4
c. 5
d. 6
68. 25. The sound pressure level is
increased by _____ dB if the intensity is
doubled.
a. 3
b. 4
c. 5
d. 6
69. 26. If four identical sounds are added
what is the increase in level in dB?
a. 3
b. 4
c. 5
d. 6
70. 27. A unit of noisiness related to the
perceived noise level
a. Noy
b. dB
c. Sone
d. Phon
71. 28. What is the loudness level of a 1KHz
tone if its intensity is 1 x 10-
5W/cm2?
a. 100 phons
b. 105 phons
c. 110 phons
d. 100 phons
72. 29. What is the unit of loudness of an
individual listener?
a. Sone
b. Phon
c. Decibel
d. Mel
73. 30. It is the weakest sound that average
human hearing can detect.
a. SPL = 0 dB
b. Threshold of hearing
c. Reference pressure = 2 x 10-5N/m2
d. A, b, c
74. 31. When waves bend away from straight
lines of travel, it is called
a. Reflection
b. Diffraction
c. Rarefaction
d. Refraction
75. 32. The amplitude of sound waves, the
maximum displacement of each air particle,
is the property which perceive as _____ of a
sound
a. Pitch
b. Intensity
c. Loudness
d. Harmonics
76.
77. Room Acoustics
Room Acoustics
Concerned with the behavior of sound
within an enclosed space with a view to
obtaining the optimum acoustic effect on
the occupants
79. Room Acoustics
Requirements
Adequate amount of sound must reach all
parts of the room.
Even distribution of sound
Noise must be reduced to an acceptable
level.
Optimum Reverberation time, RT60
80. Reverberation
Reverberation
Tendency for the sound to persist over a
definite period of time after it has been
produced originally and stopped at the
source.
82. Reverberation
Reverberation Time, RT60
Time taken for the density of sound energy
in the room to drop to 1 millionth (60dB)
below of its initial value
85. TYPES OF ROOM
LIVE ROOM
- Little absorption (RT60 > 1 sec)
DEAD ROOM
- Large absorption (RT60 < 1 sec)
ANECHOIC ROOM
- 100% absorption (free field conditions)
86. Room Acoustics
Coefficient of absorption, α
Ratio of incident sound and absorbed sound
Efficiency of sound absorption
89. Reverberation Time
Equations
a. Sabine’s Equation
For actual reverberation time with average
absorption less than or equal to 0.2; (absorption
coefficient, α ≤ 0.2)
Where;
V = room volume,
m3
A = total absorption
units
91. Reverberation Time
Equations
33.Calculate the reverberation time of a
broadcast studio 8 ft. high by 13 ft
wide by 20 ft. long. The material used
has a total absorption of 180.75
sabines.
92. Reverberation Time
Equations
b. Norris – Eyring Equation
For actual reverberation time with average
absorption greater than 0.2; ( α ≥ 0.2 )
Where;
V = room volume, m3
α = average coefficient
of reflecting surfaces
93. Reverberation Time
Equations
34. A lecture room, 16 m. long, 12.5 m.
wide and 5 m. high has a reverberation
time of 0.75 sec. Calculate the average
absorption coefficient of the surfaces
using the Eyring formula.
94. Reverberation Time
Equations
c. Stephens and Bate Equation
For ideal reverberation time computation
Where:
r = 4 for speech
r = 5 for orchestra
r = 6 for choir
95. Optimum Volume / person
Concert Halls 7.1
Italian type opera houses 4.2 – 5.1
Churches 7.1 – 9.9
Cinemas 3.1
Rooms for Speeches 2.8
96. Reverberation Time
Equations
35. Suggest the optimum volume and
reverberation time for a concert hall to
be used mainly for orchestral music
and to hold 450 people.
97. 36. A church has an internal volume of
2550 cu.m. When it contains
absorption of 186 metric sabines, what
will be its reverberation time in sec.?
a. 2
b. 2.2
c. 2.5
d. 3.0
98. 37. The transmission of sound from one room
to an adjacent room, via common walls,
floors or ceilings.
a. Flanking transmission
b. Reflection
c. Refraction
d. Reverberation
99. 38. _____ is the continuing presence of an
audible sound after the sound source has
stop.
a. Flutter echo
b. Sound concentration
c. Sound shadow
d. Reverberation
100. 39. Required time for any sound to decay
to 60 dB
a. Echo time
b. Reverberation time
c. Delay time
d. Transient time
101. 40. A room containing relatively little
sound absorption
a. Dead room
b. Anechoic room
c. Live room
d. Free-field
102. 41. A room in which the walls offer essentially
100% absorption, therefore simulating free
field conditions.
a. Dead room
b. Anechoic room
c. Live room
d. Closed room
103. 42. Calculate the reverberation time of the
room, which has a volume of 8700 ft3 and
total sound absorption 140 sabines.
a. 0.3 sec
b. 3.5 sec
c. 3 sec
d. 0.53 sec
104. 43. _____ is early reflection of sound.
a. Echo
b. Pure sound
c. Reverberation
d. Intelligible sound
106. Microphone
An acoustic device classified as a transducer
which converts sound waves into their
corresponding electrical impulses
Transducer
A device which when actuated by energy in
one transmission system, supplies energy in
the same form or in another form, to a
second transmission system
107. Classification of
Microphones
A. General Categories
1. Passive (Generator Type) Microphone
Does not require external power source
2. Active (Amplifier Type) Microphone
Needs an external power source for its
operation
112. Classification of
Microphones
D. According to Elements Used
1. Dynamic
Uses the principle of electromagnetic
induction
Electromagnetic moving coil microphone
A medium-priced instrument of high
sensitivity
124. Characteristics of
Microphone
1. Frequency Response
Frequency over which the microphone will
operate normally
Magnetic : 60 – 10 000Hz
Crystal : 50 – 10 000Hz
Condenser : 50 – 15 000Hz
Carbon : 200 – 3 000Hz
125. Characteristics of
Microphone
2. Sensitivity
Ability of the microphone to detect very
slight changes of sound.
3. Dynamic Range
Range of sound intensity that would be
covered by the microphone
126. Special Types of
Microphones
Line Microphone
Capable of picking up sound from a great
distance at an angle of 45 degrees and is
highly sensitive
128. 53. A transducer that converts acoustic
signals into electrical signals.
a. microphone
b. loudspeaker
c. both a and b
d. none of these
129. 54. A characteristic of a microphone which
indicates the frequency range over which
the microphone the frequency range over
which the microphone will operate
normally.
a. sensitivity
b. frequency response
c. dynamic range
d. directional characteristic
130. 55. An ability of the microphone to detect very
slight changes of sound.
a. sensitivity
b. frequency response
c. dynamic range
d. directional characteristic
131. 56. The range of sound intensity that would
be covered by the microphone.
a. sensitivity
b. frequency response
c. dynamic range
d. directional characteristic
132. 57. It is an audio transducer that converts
acoustic pressure in air into its equivalent
electrical impulses
a. Loudspeaker
b. Amplifier
c. Baffle
d. Microphone
133. 58. _____ is a pressure type microphone with
permanent coil as a transducing element.
a. Dynamic
b. Condenser
c. Magnetic
d. Carbon
134. 59. A microphone which has an internal
impedance of 25 kΩ is _____ type.
a. High impedance
b. Low impedance
c. Dynamic
d. Magnetic
135. 60. A microphone that uses the
piezoelectric effect
a. Dynamic
b. Condenser
c. Crystal
d. Carbon
136. 61. It describes the output of a
microphone over a range of frequencies.
a. Directivity
b. Sensitivity
c. Frequency response
d. All of the above
137. 62. A special microphone characterized by a
long perforated tube and high sensitivity,
suitable for TV applications.
a. line microphone
b. dynamic microphone
c. differential microphone
d. ribbon microphone
138. 63. Using a microphone at less than the
recommended working distance will
create a _____ which greatly increases
the low frequency signals.
a. Roll-off
b. Proximity effect
c. Drop out
d. None of the choices
141. Types of Loudspeakers
Direct Radiator Type
Those in which the vibrating surface
(diaphragm) radiates sound directly into the
air
1. Dynamic or Moving Coil Loudspeaker
Makes use of a moving coil in a magnetic
field and a permanent magnet
144. Types of Loudspeakers
Horn Type
Those in which a horn is interposed between the
diaphragm and the air
Used for efficient coupling of sound into the air
Types:
Conical Horn
Parabolic Horn
Exponential Horn
Hyperbolic Horn
145. Types of Loudspeakers
To cover the entire range of audible
frequencies, the following speakers
are used:
151. Loudspeaker Phasing
When more than one speaker is used:
Phasing must be uniform
Polarities and voice coils are in phase such
that the cone of all the speakers move
inwards at the same instant.
153. DOLBY DIGITAL
Dolby Digital is the name for audio
compression technologies developed by
Dolby Laboratories. It was originally named
Dolby Stereo Digital until 1994. Except for
Dolby TrueHD, the audio compression is
lossy.
155. DOLBY DIGITAL
The first use of Dolby Digital was to provide
digital sound in cinemas from 35mm film
prints. It is now also used for other
applications such as HDTV broadcast,
DVDs, Blu-ray Discs and game consoles.
156. DIGITAL THEATRE SOUND
DTS is a series of multichannel audio
technologies owned by DTS, Inc. (formerly
known as Digital Theater Systems, Inc.), an
American company specializing in digital
surround sound formats used for both
commercial/theatrical and consumer grade
applications. It was known as The Digital
Experience until 1995.
157. DIGITAL AUDIO
BROADCASTING
Digital Audio Broadcasting (DAB) is a
digital radio technology for broadcasting
radio stations, used in several countries,
particularly in Europe. As of 2006,
approximately 1,002 stations worldwide
broadcast in the DAB format.[1]
158. 64. An amplifier can deliver 100 W to a
loudspeaker. If the rated efficiency of the
loudspeaker is -60 dB. What is the
maximum intensity 300 ft from it?
a. 10 dB
b. 20 dB
c. 30 dB
d. 40 dB
159. 65. Speaker is a device that
a. Converts sound waves into current
and voltage
b. Converts current variations into
sound waves
c. Converts electrical energy to
mechanical energy
d. Converts electrical energy to
electromagnetic energy
160. 66. The impedance of most drivers is about
_____ ohms at their resonant frequency.
a. 4
b. 6
c. 8
d. 10
161. 67. It is a transducer used to convert
electrical energy to mechanical energy.
a. Microphone
b. Baffle
c. Magnetic assemble
d. Driver
162. 68. It is an enclosure used to prevent front
and back wave cancellation.
a. Loudspeaker
b. Driver
c. Baffle
d. Frame
163. 69. A circuit that divides the frequency
components into separate bands in order to
have individual feeds to the different
drivers.
a. Suspension system
b. Dividing network
c. Magnet assembly
d. Panel board
164. 70. What is a device that is used to measure
the hearing sensitivity of a person?
a. Audiometer
b. OTDR
c. SLM
d. Spectrum analyzer
165. 71. _____ is a type of loudspeaker driver with
an effective diameter of 5 inches used at
midrange audio frequency.
a. Tweeter
b. Woofer
c. Mid-range
d. A or C
166. 72. _____ is measure of how much sound is
produced from the electrical signal.
a. Sensitivity
b. Distortion
c. Efficiency
d. Frequency response
167. 73. A loudspeaker radiates an acoustic
power of 1 mW if the electrical input is
10 W. What is its rated efficiency?
a. -10 dB
b. -20 dB
c. -30 dB
d. -40 dB
168. 74. What is the device used in measuring
sound pressure levels incorporating a
microphone, amplification, filtering and a
display.
a. Audiometer
b. OTDR
c. SLM
d. Spectrum analyzer
169. 75. It is the device used to calibrate an
SLM?
a. Microphone
b. Pistonphone
c. Telephone
d. Filter
170. 76. Noise reduction system used for film
sound in movie.
a. Dolby
b. DBx
c. dBa
d. dBk