1. Consumer Electronics(22425)P 03 02

2. Examination Scheme
Theory
Practical
ESE PA
TOTAL 70 30
100 25 50

3. Unit 01 Audio Fundamentals
-08 Marks

4. Course Outcome
Troubleshoot different types of microphones and speakers

5. Content The Physics of Sound Sound and the Ear
The Cochlea(Inner ear)
Mental Processes
Level and Loudness
Pitch
Frequency Response and Linearity
Audio Level Metering
Acoustic Intensity Level, Acoustic Power Level, Acoustic Pressure Level

6. Content The Decibel in Acoustics Inverse Square Law
The VU and the Volume Indicator Instrument
The Phon
Velocity of Sound
Reflection and Refraction
Absorption
Root Mean Square Measurements
Selection of sound absorbing materials
Architectural Acoustics

7. The Physics of Sound
In a medium filled with fluid like air or water, any change of distribution(Pressure) of the fluid or the velocity of fluid causes vibrations
Normally, in a room filled with air, the air molecules are colliding and rebounding with room walls
If a wall of the room is moved inside the room the rebounding is faster and if the wall is moved outside the room the rebounding is slower

8. The Physics of Sound
The sound waves are caused by vibrations in any medium
Speed of sound is 344m/s(1234 Km/hour)
Like all other energies sound energy also follows the
E = mc2 relationship

9. The Physics of Sound Sound also can pass through solids.
As the medium gets denser, the velocity of sound gets increased.
Unlike electronic signals, sound is a mechanical wave
For humans, hearing is normally limited to frequencies between about 20 Hz and 20,000 Hz (20 kHz)

10. Sound and the Ear
Ear is the organ in the body that senses the intensity and frequencies present in the sound
Audio equipments can only be designed well with agood knowledge of the human hearing mechanism
The hearing sense results from acoustic, mechanical, hydraulic, nervous, and mental processes in the ear/brain combination, leading to the term psychoacoustics
Psychoacoustics is the branch of science studying the psychological and physiological responses associated with sound (including speech and music)

11. Sound and the Ear: Structure of the

12. Sound and the Ear: Structure of the
The organization of the ear is divided into 3 parts: Outer , middle and inner ear
The outer ear works at low impedance, the inner ear works at high impedance, and the middle ear is an impedance matching device
The visible part of the outer ear is called the pinna, which plays a subtle role in determining the direction of arrival of sound at high frequencies
It is too small to have any effect at low frequencies
Incident sound enters the auditory canal or meatus

13. Sound and the Ear: Structure of the
Sound vibrates the eardrum or tympanic membrane, which seals the outer ear from the middle ear
The inner ear or cochlea works by sound traveling though a fluid
Sound enters the cochlea via a membrane called the oval window
If airborne sound were to be incident on the oval window directly, the serious impedance mismatch would cause most of the sound to be reflected
The middle ear remedies that mismatch by providing a mechanical advantage

14. Sound and the Ear: Structure of the
middle ear
The tympanic membrane is linked to the oval window by three bones known as ossicles, which act as a lever system such that a large displacement of the tympanic membrane results in a smaller displacement of the oval window but with greater force

15. Sound and the Ear: Structure of the
middle ear
The malleus applies a tension to the tympanic membrane, rendering it conical in shape
The incus acts on the stapes through a spherical joint
The middle ear is normally sealed, but ambient pressure changes will cause static pressure on the tympanic membrane, which is painful
The pressure is relieved by the Eustachian tube, which opens involuntarily while swallowing
The Eustachian tubes open into the cavities of the head and must normally be closed to avoid one’s own speech appearing deafeningly loud

16. Sound and the Ear: Structure of the
middle ear
The middle ear reflex is an involuntary tightening of the tensor tympani and stapedius muscles, which heavily damp the ability of the tympanic membrane and the stapes to transmit sound by about 12 dB at frequencies below 1 kHz
The main function of this reflex is to reduce the audibility of one’s own speech
However, loud sounds will also trigger this reflex, which takes some 60 to 120 ms to occur, too late to protect against transients such as gunfire

17. The Cochlea
The cochlea is a tapering spiral cavity within bony walls, which is filled with fluid
The widest part, near the oval window, is called the base and the distant end is the apex

18. The Cochlea
The cochlea is divided lengthwise into three volumes by Reissner’s membrane and the basilar membrane
The scala vestibuli and the scala tympani are connected by a small aperture at the apex of the cochlea known as the helicotrema

19. The Cochlea
The vibration of the basilar membrane is sensed by the organ of Corti, which runs along the center of the cochlea
The deflection of hair cells in the organ of Corti triggers nerve firings and these signals are conducted to the brain by the auditory nerve
The basilar membrane is not uniform, but tapers in width and varies in thickness in the opposite sense to the taper of the cochlea
The part of the basilar membrane that resonates as aresult of an applied sound is a function of the frequency

20. The Cochlea
The distance from the apex where the maximum resonance occurs is a logarithmic function of the frequency
Essentially the basilar membrane is a mechanical frequency analyzer

21. Mental Processes
The nerve impulses are processed in specific areas of the brain that appear to have evolved at different times to provide different types of information.
The time domain response works quickly primarily aiding the direction-sensing mechanism and is older in evolutionary terms
The frequency domain response works more slowly, aiding the determination of pitch and timbre and evolved later, presumably as speech evolved.
In early times, the most important aspect of the hearing mechanism was the ability to determine the location of the sound source

22. Mental Processes
As shown in figure, the brain can examine several possible differences between the signals reaching the two ears.

23. Mental Processes
At high frequencies the sound becomes directional enough for the head to shade the distant ear, causing what is called interaural intensity difference
Phase differences are only useful at low frequencies and shading only works at high frequencies
A transient has a unique aperiodic waveform, which suffers no ambiguity in the assessment of interaural delay (IAD) between two versions
A one-degree change in sound location causes an IAD of around 10 μs
The smallest detectable IAD is a 6 μ s. This should be the criterion for spatial reproduction accuracy

24. Mental Processes
Transient noises produce a pressure step whose source is accurately and instinctively located

25. Mental Processes
The time of arrival of the transient at the two ears will be different and will locate the source laterally within a processing delay of around a millisecond.
Following the event that generated the transient, the air pressure equalizes
The time taken for this equalization varies and allows the listener to establish the likely size of the sound source
In an audio system that claims to offer any degree of precision, every component must be able to reproduce transients accurately

26. Level and Loudness
The ear can detect a sound pressure variation of only
2x105 Pascals root mean square (rms) and so this figure is used as the reference against which the sound pressure level (SPL) is measured
The sensation of loudness is a logarithmic function of SPL; consequently, a logarithmic unit, the decibel, was adopted for audio measurement
The dynamic range of the ear exceeds 130 dB, but at the extremes of this range, the ear either is straining to hear or is in pain

27. Level and Loudness
The frequency response of the ear is not at all uniform and it also changes with SPL
The subjective response to level is called loudness and is measured in phons
The phon scale is defined to coincide with the SPL scale at 1 kHz, but at other frequencies the phon scale deviates because it displays the actual SPLs judged by a human subject to be equally loud as a given level at 1 kHz

28. Level and Loudness

29. Level and Loudness
Loudness is a subjective reaction and is almost impossible to measure
In addition to the level-dependent frequency response problem, the listener uses the sound not for its own sake but to draw some conclusion about the source
For example, most people hearing a distant motorcycle will describe it as being loud. Clearly, at the source, it is loud, but the listener has compensated for the distance

30. Pitch
Pitch is an auditory perceptual property that allows the ordering of sounds on a frequency-related scale
 Pitches are compared as "higher" and "lower" in the sense associated with musical melodies which require "sound whose frequency is clear and stable enough to be heard as not noise”
Pitch is a major auditory attribute of musical tones, along with duration, loudness, and timbre
Pitch may be quantified as a frequency, but pitch is not a purely objective physical property; it is a subjective psycho acoustical attribute of sound

31. Frequency Response and
Linearity
It is a goal in high-quality sound reproduction that the timbre of the original sound shall not be changed by the reproduction process

32. Frequency Response and
Linearity
Fundamental requirement for quality sound reproduction is that the response to all frequencies should be equal
Frequency response is easily tested using sine waves of constant amplitude at various frequencies as an input and noting the output level for each frequency
Another way in which timbre can be changed is by nonlinearity

33. Frequency Response and
Linearity
All audio equipment has a transfer function between the input and the output, which form the two axes of a graph
Unless the transfer function is exactly straight or linear , the output waveform will differ from the input

34. Frequency Response and
Linearity
A nonlinear transfer function will cause distortion, which changes the distribution of harmonics and changes timbre

35. The Decibel
The decibel is a logarithmic measuring system and has its origins in telephony where the loss in a cable is a logarithmic function of the length
Human hearing also has a logarithmic response with respect to sound

36. Fidelity
Fidelity is the quality of faithfulness or loyalty. Its original meaning regarded duty in a broader sense than the related concept of fealty. Both derive from the Latin word fidēlis, meaning "faithful or loyal".
In audio, "fidelity" denotes how accurately a copy reproduces its source. 

37. Velocity of Sound
For a given frequency, the relation of the wavelength to the velocity of sound in the medium is
Where c is velocity of sound in m/s
In dealing with many acoustic interactions, the wavelength involved is significant and the ability to calculate it is important.
Therefore we need to be able to both calculate and measure the velocity of sound quickly and accurately

38. Velocity of Sound
The velocity of sound varies with temperature to adegree sufficient to require our alertness to it
The velocity of sound under conditions likely to be encountered in connection with architectural acoustic considerations is dependent on three fundamental factors
1) γ is the ratio of specific heats and is for diatomic molecules (air molecules)
2) PS is the equilibrium gas pressure in Newtons per square meter ( N/m2 )
3) ρ is the density of air in kilograms per cubic meter (kg/m3 )

39. Velocity of Sound The formula for velocity of sound is as follows
The density of air varies with temperature, and an examination of the basic equations reveals that, indeed, temperature variations are the predominant influence on the velocity of sound in air
The velocity of sound is temperature dependent. The approximate formula for calculating velocity is

40. Velocity of Sound

41. Reflection and Refraction
Sound can be reflected by hitting an object larger than one-quarter wavelength of the sound
When the object is one-quarter wavelength or slightly smaller, it also causes diffraction of the sound (bending around the object)
Refraction occurs when the sound passes from one medium to another
The velocity of sound increases with increasing temperature

42. Reflection and Refraction
According to above equation, velocity of sound is inversely proportional to ρ density of air
ρ is inversely proportional to temperature and hence velocity of sound is directly proportional to temperature
Therefore sound emitted from a source located on the frozen surface of a large lake on a sunny day will encounter warmer temperatures

43. Reflection and Refraction
As the wave diverges upward, causing the upper part of the wave to travel faster than the part of the wave near the surface.
This causes a lens-like action to occur, which bends the sound back down toward the surface of the lake

44. Reflection and Refraction
Wind blowing against a sound source on a frozen causes temperature gradients near the ground surface that result in the sound being refracted upward
Wind blowing in the same direction as the sound produces temperature gradients along the ground surface that tend to refract the sound downward
Reflections from large boundaries, when delayed in time relative to the direct sound, can be highly destructive of speech

45. Absorption Absorption is the inverse of reflection
For a given material, the absorption coefficient ( a ) is
where EA is the absorbed acoustic energy, EI is the total incident acoustic energy and (1-a) is the reflected sound
If a material has an a of 0.25, it will absorb 25% of all sound energy having the same frequency and it will reflect 75% of the sound energy having that frequency

46. Root Mean Square Measurements
According to Ohm’s law, the power dissipated in a resistance is proportional to the square of the applied voltage
This causes no difficulty with direct current (DC), but with alternating signals such as audio it is harder to calculate the power
Consequently, a unit of voltage for alternating signals was devised
The average power delivered during a cycle must be proportional to the mean of the square of the applied voltage

47. Root Mean Square Measurements
An AC signal of a given number of volts rms will dissipate exactly the same amount of power in a given resistor as the same number of volts DC
for a sine wave the rms voltage is obtained by dividing the peak voltage Vpk by the square root of 2.
However, for a square wave the rms voltage and the peak voltage are the same

48. Root Mean Square
Measurements

49. Selection of sound absorbing
materials
A material’s sound absorbing properties can be
described as a sound absorption coefficient in a particular frequency range
Most good sound absorbers readily transmit sound
There are three basic categories of sound absorbers:
Porous materials commonly formed of matted or spun fibers
Panel (membrane) absorbers having an impervious surface mounted over an airspace
Resonators created by holes or slots connected to an enclosed volume of trapped air

50. Selection of sound absorbing
materials
Porous absorbers: Common porous absorbers include carpet, spray-applied cellulose, aerated plaster, fibrous mineral wool and glass fiber, open-cell foam, and cast porous ceiling tile
All of these materials allow air to flow into a cellular structure where sound energy is converted to heat
Porous absorbers are the most commonly used sound absorbing materials
Thickness plays an important role in sound absorption by porous materials

51. Selection of sound absorbing
materials
Porous absorbers

52. Selection of sound absorbing
materials
Panel Absorbers: Typically, panel absorbers are non- rigid, non-porous materials which are placed over an airspace that vibrates in a flexural mode in response to sound pressure exerted by adjacent air molecules
Common panel absorbers include thin wood paneling over framing, lightweight impervious ceilings and floors, glazing and other large surfaces capable of resonating in response to sound
Panel absorbers are usually most efficient at absorbing low frequencies

53. Selection of sound absorbing
materials
Panel Absorbers

54. Selection of sound absorbing
materials
Resonators: Resonators typically act to absorb sound in a narrow frequency range
Resonators include some perforated materials and materials that have openings
The resonant frequency is governed by the size of the opening, the length of the neck and the volume of air trapped in the chamber
The classic example of a resonator is the Helmholtz resonator, which has the shape of a bottle

55. Selection of sound absorbing
materials
Resonator

56. Audio Amplifier Definition-
An audio amplifier is a device used to amplify audio signals of frequency range 20Hz to 20KHz.

57. Use of Audio amplifiers
1.Outpu stage of radio receivers 2. Sound section of TV receivers 3.Record players 4. PA system 5. Tape recorder 6. Stereo systems 7. Hi-Fi equipments

58. Types of Audio Amplifiers
Types of Voltage amplifier are-
1 . Voltage Amplifier
Power Amplifier
Frequency Response of Audio Amplifier
Gain operating range depends on type of amplifier
In DB
20Hz 500Hz kHz KHz
frequency

59. Comparison of voltage and power amplifier
Sr.no.
Voltage Amplifier
Power Amplifier 1
First stage in Audio Amplifier
Last stage in audio amplifier 2
Output voltage is many times greater than inpout voltage.
Output power is many times greater than input Power. 3
Operates in class-A mode.
Operates in class-B push pull mode. 4
Controls like loudness control,bass and treble controlare used at output of voltage amplifier.
Volume control is used at power amplifier.

60. (Special)Types of Audio Amplifiers
Depending on the type of program, location, requirement and gathering of public types of Audio amplifiers are-
Monophonic (system) amplifier
Stereophonic (system) amplifier
Hi-Fi (system) amplifier
Public Address(PA system) amplifier

61. Comparison of Mono and Stereo Amplifier
Sr.No.
Mono Amplifier
Stereo Amplifier 1
Only one set of amplifier is used.
Two sets or channels of amplifiers is used. 2
Gives two dimensional sound.
Gives three dimensional sound. 3
No sense of direction.
Gives sense of direction to the listeners. 4
Lack of naturalness.
Match to human ears so naturalness

62. Block Diagram of Mono Amplifier
L.S.
Power Amplifier
Pre - Amplifier
Mic

63. Block Diagram of Stereo Amplifier
Left channel
L.S
Right channel
MIC
Pre- Amplifier
Power
Amplifier
Mic
Power
Amplifier
Pre amplifier

64. Microphone

65. What is a microphone?
A microphone is a transducer that converts acoustic energy to electrical energy.
It has many uses in today's world from medicine to musical recording.
It reacts to a pressure input by use of a diaphragm.

66. The Invention of the Microphone
1876 – Alexander Graham Bell
1878 – Hughes (First use of term ‘microphone’)
(actually, a carbon microphone )
Used for telephony
Use pressure which get converted to resistance
And done well since then

67. Pressure Type Velocity Type
Microphone
Types
Pressure Type
Velocity Type

68. Pressure Type Microphone
Diaphragm has only one surface exposed to sound waves.
Output corresponds to instantaneous pressure of the incident sound wave.

69. Pressure Microphone Carbon Microphone Crystal Microphone
Dynamic Microphone
Capacitor

70. Velocity Type Microphone
Sound waves will hit front and back surface of the diaphragm.
Types
1)Ribbon Microphone
2)Pressure microphone

71. Carbon Microphone

72. Dynamic Microphones
Dynamic moving coil microphones employ a coil of wires attached to a diaphragm, which is suspended within a magnetic field.
Acoustical vibrations cause the diaphragm and the coil to vibrate within this magnetic field, creating an AC (alternating current.)
This current electrically represents the audio signal.

73. Crystal Microphone

74. Condenser Microphones
Condenser microphones use two adjacent plates. One is stationary, while the other, a diaphragm, vibrates to incoming acoustic signal.
These two plates are charged with a constant voltage - phantom power. As the distance between the stationary plate and diaphragm varies with incoming vibrations, a varying electrical current is generated.

76. Ribbon Microphones Again principle of induction is used
Ribbon (Induction) is used as diaphragm
Oscillates between magnetic poles
Bi-directional

77. Lavalier Lavalier microphones are small,
lightweight microphones designed to be attached under the chin of the speaker.
Attached to the talker’s clothing in such a manner that they will not move and produce rustling noises.
Common in television and film production because they are easy to conceal.

78. Dynamic V/s Condenser Microphones

79. Accurate representation Low cost
Condenser Microphones Amplified transfer of energy is more than 1 Extremely accurate Higher cost Very sensitive (larger sound field) Less durable (prone to humidity and shock)
Dynamic Microphones Actual energy to energy transfer 1:1
Accurate representation Low cost
Less sensitive (smaller sound field)
More durable than other types of microphones

80. Electret Microphone

81. Electret Microphone

82. Tie Clip Microphone

83. How to Choose Microphones

84. Microphone Selection Natural, smooth tone quality
Flat frequency response
Bright, present tone quality
Presence peak (5kHz)
Extended lows
Omni condenser dynamic with extended low frequency response
Extended highs
condenser

85. Choosing a Microphone Boosted bass up close Directional mic
Reduced leakage, reduced room acoustics
Directional
Enhanced acoustic
Omni
Miking close to a surface
Boundry (TMZ)

86. Choosing a Mic Coincident or near-coincident Stereo mic
Extra ruggedness
Dynamic
Distortion-free pick-up of loud sounds
Condenser with high SPL spec or dynamic
Low self-noise, high sensitivity, noise-free pickup of quiet sounds
Large-diaphragm condenser mic

87. Microphone Pickup Patterns
Pickup patterns help to reduce unwanted signal from
getting pickups
Popular patterns: Monodirectional, Bidirectional, Cardioid, and Omnidirectional 15

88. Omnidirectional Microphones16
Omnidirectional Microphones
collects sound from all around
360 degrees.
A true omni-directional mic is a pure pressure transducer - it strictly measures changes in pressure without any regard to
the direction that the wave is
traveling.
microphone can be
share by the group.

89. Bidirectional Microphones17
Bidirectional Microphones
Bidirectional = two directions.
A true bidirectional mic can be a pressure-gradient or velocity transducer, meaning its response to the sound will depend on the direction the sound wave is coming from.
The diaphragm is completely open on both sides so that it can react to pressure changes on either side of the diaphragm
This results in a “figure-8” pattern - it is sensitive only to sounds arriving from directly in front or directly behind

90. Unidirectional/Cardioid18
Unidirectional/Cardioid
Unidirectional = one direction
collects most of the sound from the front, and very little from the back and sides.
The microphone has a null at degrees - it will not respond to sound approaching directly from the rear.
This results in a “heart- shaped” pattern (cardio=heart)

91. Other patterns 19
Super- and Hyper-cardioid mic’s are cardioids that use more bidirectional in the “recipe.” This results in a more narrow pickup in the front and a small pickup lobe in the rear. The nulls are moved to 120 or 110 degrees.
Shotgun - uses an interference tube to get a very narrow forward pickup. The longer the tube, the more narrow the pickup.
Shotgun

92. Types of Microphone Lavaliere (Tie-Pin) Microphone20
Types of Microphone
Handheld Microphone
Lavaliere (Tie-Pin) Microphone
Surface Mount Microphone
Shotgun Microphone
Wireless Microphone System

93. 21
Accessories
Wind screen / Pop filter: reduces “popping” caused by low frequencies overloading the mic. Breath or wind may cause noise and/or pops.
Types: Foam cover or Screen
Shock Mount: Reduces unwanted mechanical vibrations from the mic stand into the microphone body.

94. Cordless microphone system

95. Applications Telephones, Hearing aids,22
Telephones,
Hearing aids,
Public address systems for concert halls and public events,
Motion picture production,
Live and recorded audio engineering,
Two-way radios
Megaphones, radio and television broadcasting
In computers for recording voice, speech recognition

96. Speaker

97. An electro-acoustic transducer that converts electrical signals into sounds loud enough to be heard at a distance.
Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful.
The most common form of loudspeaker uses a paper cone supporting a voice coil electromagnet acting on a permanent magnet.

98. Characteristics of Loudspeaker
Directivity
Signal to noise ratio
Efficiency
Frequency Response
Distortion
Speaker coil impedance
Power handling Capacity

99. Types Moving Coil or Cone type Loudspeaker Electro dynamic Loudspeaker
Electrostatic Loudspeaker
Horn Type Loudspeaker

100. Moving Coil or Cone type

101. Electro dynamic Electrodynamic

102. Electrostatic Loudspeaker

103. Electrodynamic

105. HORNS Horns were the earliest form of amplification.
Horns do not use electricity. The problem with horns is that they could not amplify the sound very much.
Horns remain a novelty for collectors today.
Audio Recording for entertainment and recorded keeping, later on for voice radio

106. ELECTRODYNAMIC LOUDSPEAKER
This is a device that uses an electromagnetic coil and diaphragm to create sound. It uses an electromagnet to turn electric signals of varying strength into movement. This is the most common type of speaker in the world today.