Types of loud speakers and microphones are discussed. Principles of sound sensing and production are explained.

1. Audio Devices and Applications

2. Contents
 Microphone Sensitivity
 Nature of Response and Directional Characteristics
 Measurement Microphones
 Various Types of Microphones
 Various Types of Loudspeakers
 Characteristic Impedance of Loud Speakers
 Headphone Types
 The basics of Magnetic Recording
 Sound Cards, Sound Mixers
 PA Systems & Installations
 Digital Consoles

3. Microphone working

4. Microphone Sensitivity
 Sensitivity is an important characteristic of
microphone
 It tells that how much electrical output a microphone
has produced for a certain sound pressure level
 For a same sound pressure level input if two
microphones are producing different electrical outputs
then the microphone with higher electrical output is
said to be more sensitive
 Sensitivity is defined as output in millivolts for the
sound pressure of 1 pascal at 1 Khz

5. Measuring microphone sensitivity

6. Microphone Sensitivity
 Select a measuring point (about 5 to 6 ft) in front of
the loudspeaker and place the SLM there
 Adjust the system until the SLM reads 94 dB (a band
of pink noise from250 to 5000 Hz is excellent for this
purpose)
 Now substitute the microphone to be tested for the
SLM
 Take the microphone open circuit voltage reading on
the micro-voltmeter

7. Nature of Response and Directional
Characteristics
 A controlled directional response can be obtained by
employing a sensing diaphragm, both faces of which
are exposed to the sound field of interest
 Such diaphragms experience a driving force that
depends on the spatial rate of change of pressure
rather than on the pressure itself
 The diaphragm may be circular as in a capacitor or
moving coil microphone or rectangular as in a ribbon
microphone
 The principal axis of the microphone is directed
perpendicular to the plane containing the diaphragm

8. Nature of Response and Directional
Characteristics
 This axis makes an angle θ
with the direction of the
incident sound
 When θ has the value π /2,
both faces of the
diaphragm experience
identical pressures and the
net driving force on the
diaphragm is zero

9. Nature of Response and Directional
Characteristics
 Now when θ is 0, the sound wave is incident normally
on the diaphragm and the driving force on the left face
of the diaphragm will be the pressure in the sound
wave at the left face’s location multiplied by the area of
the left face
 The pressure difference can be calculated by taking the
product of the space rate of change of acoustic
pressure, known as the pressure gradient, with the
effective acoustical distance separating the two sides of
diaphragm

10. Nature of Response and Directional
Characteristics

11. Frequency response of microphone
 Frequency response refers to the way a microphone
responds to different frequencies
 It is a characteristic of all microphones that some
frequencies are magnified and others are attenuated
 For example, a frequency response which favors high
frequencies means that the resulting audio output will
sound more trebly than the original sound
 For high quality instrument grade microphones a large
flat range (20Hz to 20KHz) is required

12. Frequency response of microphone

13. Measurement Microphones
 Some microphones are intended for testing speakers,
measuring noise levels and otherwise quantifying an
acoustic experience
 These are calibrated transducers and are usually
supplied with a calibration certificate that states
absolute sensitivity against frequency
 Measurement microphones are dominantly air
capacitor or electret capacitor microphones
 While ceramic piezoelectric units may still be
encountered

14. Measurement Microphones
 The standard sizes in terms of capsule diameter are 1
inch, 1/2 inch, 1/4 inch, and 1⁄8 inch
 The larger units have higher sensitivity and lower noise
floors
 The 1-inch unit is favored for making measurements in
quiet environments at frequencies below about 8 kHz
 The ½ inch unit is a general purpose one but has high
frequency limitations
 Broad frequency band measurements usually require
the 1/4 or 1⁄8 -inch variety

15. Measurement Microphones
 When the microphone capsules are smaller than 1/2
inch in diameter it is impossible to incorporate the
necessary circuitry and connector in a uniform
cylinder having a diameter equal to that of the capsule
 In such instances it is necessary to enclose the
circuitry and connector in a larger cylinder that is
joined to the capsule by a smoothly tapered section
matching the larger diameter to the smaller diameter

16. Various Types of Microphones
 Various types of microphones are available in the
market as listed below
 Moving coil(dynamic microphone)
 Ribbon
 Carbon microphone
 Condenser
 Electret
 Crystal(Piezoelectic microphone)

17. Various Types of Microphones
 Fiber optic microphone
 laser microphone
 Water microphone
 Microelectromechanical systems(MEMS microphone)

18. Moving coil(dynamic microphone)
 Dynamic microphones work via electromagnetic
induction
 They are robust, relatively inexpensive and resistant to
moisture
 With moving coil microphones a small movable
induction coil is attached to the diaphragm
 When the diaphragm vibrates, the coil moves in the
magnetic field, producing a varying current in the coil
through electro-magnetic induction

19. Moving coil(dynamic microphone)
 These are the advantages of this microphone type:
- Relatively robust to mechanical stress
- High SPL capability (useful when singing or playing loud
instruments)
- No supply voltage needed
 Due to the coil mass, moving coil microphones provide a
limited reproduction spectrum and poor pulse behavior
 They are suitable for close miking, because non-linear
distortions are rare with high sound pressure levels
 They are primarily used for live applications, sometimes
also in the studio.

20. Moving coil(dynamic microphone)

21. Ribbon microphone
 Ribbon microphones use a thin, usually corrugated
metal ribbon suspended in a magnetic field
 The ribbon is electrically connected to the
microphone's output, and its vibration within the
magnetic field generates the electrical signal
 Basic ribbon microphones detect sound in a bi-
directional (also called figure-eight) pattern because
the ribbon, which is open to sound both front and
back, responds to the pressure gradient rather than the
sound pressure

22. Ribbon microphone

23. Ribbon microphone

24. Carbon microphone
 A carbon microphone uses a capsule or button containing
carbon granules pressed between two metal plates
 A voltage is applied across the metal plates, causing a small
current to flow through the carbon
 One of the plates, the diaphragm, vibrates in sympathy
with incident sound waves, applying a varying pressure to
the carbon
 The changing pressure deforms the granules, causing the
contact area between each pair of adjacent granules to
change, and this causes the electrical resistance of the mass
of granules to change

25. Carbon microphone
 The changes in resistance cause a corresponding
change in the current flowing through the
microphone, producing the electrical signal
 Carbon microphones were once commonly used in
telephones; they have extremely low-quality sound
reproduction and a very limited frequency response
range, but are very robust devices
 Unlike other microphone types, the carbon
microphone can also be used as a type of amplifier,
using a small amount of sound energy to control a
larger amount of electrical energy

26. Carbon microphone

27. Condenser microphone
 The condenser microphone, invented at Bell Labs in
1916 by E. C. Wente is also called a capacitor
microphone or electrostatic microphone — capacitors
were historically called condensers
 Here, the diaphragm acts as one plate of a capacitor,
and the vibrations produce changes in the distance
between the plates
 There are two types, depending on the method of
extracting the audio signal from the transducer: DC-
biased and radio frequency (RF) or high frequency
(HF) condenser microphones

28. Condenser microphone
 With a DC-biased microphone, the plates are biased
with a fixed charge (Q)
 The voltage maintained across the capacitor plates
changes with the vibrations in the air, according to the
capacitance equation (C = Q⁄V), where Q = charge in
coulombs, C = capacitance in farads and V = potential
difference in volts
 RF condenser microphones use a comparatively low RF
voltage, generated by a low-noise oscillator.

29. Condenser microphone
 Condenser microphones span the range from
telephone transmitters through inexpensive karaoke
microphones to high-fidelity recording microphones
 They generally produce a high-quality audio signal and
are now the popular choice in laboratory and
recording studio applications
 They require a power source, provided either via
microphone inputs on equipment from a small battery
 Power is necessary for establishing the capacitor plate
voltage, and is also needed to power the microphone
electronics

30. Condenser microphone

31. Electret microphone
 An electret microphone is a type of capacitor
microphone
 The externally applied charge under condenser
microphones is replaced by a permanent charge in an
electret material
 An electret is a ferroelectric material that has been
permanently electrically charged or polarized
 Nearly all cell-phone, computer, headset microphones
are electret types

32. Electret microphone

33. Crystal microphone
 A crystal microphone microphone uses the phenomenon
of piezoelectricity — the ability of some materials to
produce a voltage when subjected to pressure — to
convert vibrations into an electrical signal
 The high impedance of the crystal microphone made it
very susceptible to handling noise, both from the
microphone itself and from the connecting cable
 Piezoelectric transducers are often used as contact
microphones to amplify sound from acoustic musical
instruments, to sense drum hits, for triggering electronic
samples, and to record sound in challenging
environments, such as underwater under high pressure

34. Crystal microphone

35. Fiber optic microphone
 A fiber optic microphone converts acoustic waves into
electrical signals by sensing changes in light intensity
 During operation, light from a laser source travels through
an optical fiber to illuminate the surface of a reflective
diaphragm
 Sound vibrations of the diaphragm modulate the intensity
of light reflecting off the diaphragm in a specific direction
 The modulated light is then transmitted over a second
optical fiber to a photo detector, which transforms the
intensity-modulated light into analog or digital audio for
transmission or recording

36. Fiber optic microphone
 Fiber optic microphones do not react to or influence any
electrical, magnetic, electrostatic or radioactive fields
 Fiber optic microphones are robust, resistant to
environmental changes in heat and moisture, and can
be produced for any directionality or impedance
matching
 The distance between the microphone's light source and
its photo detector may be up to several kilometers
without need for any preamplifier or other electrical
device, making fiber optic microphones suitable for
industrial and surveillance acoustic monitoring

37. Fiber optic microphone

38. Laser microphone
 Laser microphones are often portrayed in movies as
spy gadgets, because they can be used to pick up
sound at a distance from the microphone equipment
 A laser beam is aimed at the surface of a window or
other plane surface that is affected by sound
 The vibrations of this surface change the angle at
which the beam is reflected, and the motion of the
laser spot from the returning beam is detected and
converted to an audio signal

39. Laser microphone

40. Water microphone
 Early microphones did not produce intelligible
speech, until Alexander Graham Bell made
improvements including a variable resistance
microphone/ transmitter
 Bell's liquid transmitter consisted of a metal cup filled
with water with a small amount of sulfuric acid added
 A sound wave caused the diaphragm to move, forcing a
needle to move up and down in the water
 The electrical resistance between the wire and the cup
was then inversely proportional to the size of the water
meniscus around the submerged needle

41. Water microphone
 The famous first phone conversation between Bell and
Watson took place using a liquid microphone

42. MEMS microphone
 The MEMS (MicroElectrical-Mechanical System)
microphone is also called a microphone chip or silicon
microphone
 The pressure-sensitive diaphragm is etched directly into a
silicon chip by MEMS techniques, and is usually
accompanied with integrated preamplifier
 Most MEMS microphones are variants of the condenser
microphone design
 Often MEMS microphones have built in analog-to-digital
converter (ADC) circuits on the same CMOS chip making
the chip a digital microphone and so more readily
integrated with modern digital products

43. MEMS microphone

44. Loudspeaker working

45. Loudspeaker working
 The loudspeakers in radio, television or stereo system
consists of a permanent magnet surrounding an
electromagnet that is attached to the loudspeaker
membrane or cone
 By varying the electric current through the wires
around the electromagnet, the electromanget and the
speaker cone can be made to move back and forth
 If the variation of the electric current is at the same
frequencies of sound waves, the resulting vibration of
the speaker cone will create sound waves, including
that from voice and music

46. Various Types of Loudspeakers
 Crystal loudspeaker(Piezoelectric speakers)
 Dipole loudspeaker
 Electrostatic loudspeaker
 Dynamic loudspeaker
 Permanent magnet loudspeaker
 Woofers
 Midrange
 Tweeter

47. Crystal loudspeaker(Piezoelectric
speakers)
 Piezoelectric speakers are frequently used as beepers in
watches and other electronic devices
 Piezoelectric speakers are resistant to overloads that would
normally destroy most high frequency drivers, and they can
be used without a crossover due to their electrical
properties
 There are also disadvantages: some amplifiers can oscillate
when driving capacitive loads like most piezoelectric,
which results in distortion or damage to the amplifier
 Frequency response is inferior to that of other technologies

48. Crystal loudspeaker(Piezoelectric
speakers)
 Piezoelectric speakers can have extended high
frequency output, and this is useful in some
specialized circumstances; for instance, sonar
applications in which piezoelectric variants are used as
both output devices and input devices

49. Dipole loudspeaker
 A dipole speaker enclosure in its simplest form is
constructed by mounting a loudspeaker driver on a flat
panel
 The term dipole derives from the fact that the polar
response consists of two lobes, with equal radiation
forwards and backwards
 A dipole speaker works by creating air movement (as
sound pressure waves) directly from the front and back
surfaces of the driver

50. Dipole loudspeaker

51. Electrostatic loudspeaker
 An electrostatic loudspeaker is a loudspeaker design
in which sound is generated by the force exerted on a
membrane suspended in an electrostatic field
 The speakers use a thin flat diaphragm usually
consisting of a plastic sheet coated with material such
as graphite sandwiched between two electrically
conductive grids, with a small air gap between the
diaphragm and grids
 For low distortion operation, the diaphragm must
operate with a constant charge on its surface, rather
than with a constant voltage

52. Electrostatic loudspeaker
 By means of the conductive coating and an external
high voltage supply the diaphragm is held at a DC
potential of several kilovolts with respect to the grids
 The grids are driven by the audio signal; front and rear
grid are driven in anti phase
 As a result a uniform electrostatic field proportional to
the audio signal is produced between both grids. This
causes a force to be exerted on the charged diaphragm,
and its resulting movement drives the air on either
side of it

53. Electrostatic loudspeaker

54. Dynamic loudspeaker
 These are the most common form of loudspeakers
 The voice coil in moving coil drivers is suspended in a
magnetic field provided by the loudspeaker magnet
structure
 As electric current flows through the voice coil (from
an amplifier), the magnetic field created by the coil
reacts against the magnet's fixed field and moves the
voice coil (and so the cone)
 Alternating current will move the cone back and forth

55. Dynamic loudspeaker

56. Permanent magnet loudspeaker
 Tweeters – produce the higher frequency spectrum
sounds. High frequency sounds are in the range of 2000 Hz
and up. Tweeters are very small and normally around 1 inch
in diameter
 Midrange –midrange drivers produce sounds in the
midrange frequency. This is usually in the range of 200 –
500 Hz up to 2000 – 3000 Hz. Midrange speakers size range
from 4 inches in diameter up to 8 inches in diameter
 Woofers – produce the lower frequency sounds, but don’t
necessarily have to go to bottom of the spectrum. Their
frequency range is typically from 500 Hz down to 80 Hz or
below. Woofers speakers size range from 8 to 12 inches in
diameter

57. Permanent magnet loudspeaker
 Subwoofers – produce sounds in the lowest frequency
range typically at 80 Hz and below. Ten inches and up
are typical sizes for subwoofer speakers. Subwoofers
are usually stand–alone speakers that get placed in a
corner. The reason for their large size is the
considerable amount of power required to produce low
frequency sounds. Therefore, a large amplifier with its
own power source is needed to give enough power to
the subwoofer.

58. Permanent magnet loudspeaker

59. Characteristic Impedance of Loud
Speakers
 The characteristic impedance is the ratio of the
effective sound pressure to the particle velocity at that
point in a free, plane, progressive sound wave
 It is equal to the product of the density of the medium
times the speed of sound in the medium ( p0C )
 It is analogous to the characteristic impedance of an
infinitely long, dissipation-less, transmission line
 The unit is the Rayl, or Newtons/m3

60. Headphones types
 Moving Iron
 Moving Coil
 Electrodynamics Orthodynamic
 Electrostatic
 Electrets
 High Polymer

61. Moving Iron
 Early headphones relied on many turns of wire wound
on to a magnetic yoke held close to a stiff disc made of
a “ soft ” magnetic alloy
 A permanent magnet pulled the thin disc toward the
yoke with a constant force and audio signals fed to the
coil caused this force to vary in sympathy with the
input
 They were very sensitive, needing hardly any power to
drive them, and were very poor in sound quality due to
the high mass and stiffness of the diaphragm

62. Moving Iron

63. Moving Coil
 Moving-coil headphones work in exactly the same way
as moving-coil loudspeakers
 The major difference, of course, between moving-coil
headphones and loudspeakers is that the former are
much smaller, with lighter and more responsive
diaphragms
 They can consequently sound much more open and
detailed than loudspeakers using the moving-coil
principle

64. Moving Coil

65. Electrodynamics Orthodynamic
 This type of headphone is the same family as the
moving-coil type, except that the coil has been
unwound and fixed to a thin, light, plastics diaphragm
 The ring shaped magnetic gap has been replaced by
opposing bar magnets, which cause the magnetic field
to be squashed parallel to the diaphragm
 The “ coil ” is now a thin conductor zig-zagging or
spiraling its way across the surface of the diaphragm
 Unlike the moving coil type, this headphone has flat
diaphragm

66. Electrodynamics Orthodynamic

67. Electrostatic
 The diaphragm is stretched under low mechanical
tension between two perforated conductive plates to
which the audio signals are fed via a step-up
transformer
 The central diaphragm is kept charged to a very high
voltage with respect to the outer plates using a special
type of power supply and hence it contains a static
charge and is light
 The diaphragm experiences electrostatic attraction
toward both outer plates

68. Electrostatic
 The spacing between the plates and diaphragm, the
voltage between them, and the tension on the diaphragm
are all chosen carefully so that the film does not collapse
on to either plate
 When an audio signal is fed to the transformer, it is
stepped up at the secondary from a few volts to around a
thousand volts
 This unbalances the forces on the diaphragm in sympathy
with the audio signal, causing it to be attracted alternately
to each plate and of course reproducing an analogue of the
original sound

69. Electrostatic

70. Electrets
 Basically, the electret headphone is an electrostatic
type but using a material that permanently retains
electrostatic charge
 The electret has the advantages of the conventional
electrostatic, but does not require an additional
external power supply
 It is similarly restricted in maximum sound pressure
level, although both types produce perfectly adequate
sound pressure levels with conventional power
amplifiers

71. Electrets

72. High Polymer
 High polymer is basically a generic name to cover
piezoelectric plastics films such as polyvinylidene
fluoride film
 High polymer films are very thin, some 8 to 300 μ m,
and have very low mechanical stiffness, which makes
them ideal for transducer diaphragms
 The basic film is made piezo electric by stretching it
to up to four times its original length, depositing
aluminum on each side for electrodes, and polarizing
with a high DC electric field at 80–100oC for about an
hour

73. High Polymer
 When voltage is later applied across the film, it
vibrates in a transverse direction, becoming alternately
longer and shorter
 If the material is shaped into an arc, this lengthening
and shortening are translated into a pulsating
movement, which will generate sound waves in
sympathy with the electrical input signal
 The high polymer headphone is also claimed to be
much more sensitive than the electrostatic type and
unaffected by humidity

74. High Polymer

75. The Basics of Magnetic Recording
 A sound recording is made onto magnetic tape by
drawing the tape past a recording head at a constant
speed
 The recording head (which is essentially an
electromagnet) is energized by the recording amplifier
of the tape recorder
 The electromagnet, which forms the head itself, has a
small gap so that the magnetic flux created by the
action of the current in the electromagnet’s coil is
concentrated at this gap

76. The Basics of Magnetic Recording
 Because the tape moves and the energizing signal
changes with time, a “ record ” of the flux at any given
time is stored on the tape
 Replaying a magnetic tape involves dragging the tape
back across a similar electromagnet called the
playback head

77. The Basics of Magnetic Recording
 The changing flux detected at the minute gap in the
playback head causes a current to flow in the head’s
coil
 This is applied to an amplifier to recover the
information left on the tape
 Thus in a tape recording, sound signals are recorded as
a magnetic pattern along the length of the tape
 This pattern is created due to the coating made of
ferric iron oxide or chromium dioxide on the tape
which possesses magnetic properties

78. B-H Curve
 The relation between the
magnetizing field (H) and
the resultant induction (B
in an iron
sample(assumed, initially, to
be in a completely
demagnetized condition)
may be plotted as shown in
Figure

79. Bias for magnetic tapes
 If a sound recording and reproduction system is to
perform without adding distortion, a high degree of
linearity is required
 From the B-H curve, it is apparent that the only linear
region over which this relationship holds is between B1
and B2
 For other regions, to get a distortion free output
biasing is used
 In principle, a steady magnetic force may be
applied, in conjunction with the varying force
dependent on the audio signal, thereby biasing the
audio signal portion of the overall magnetic effect into
the initial linear region of the BH loop

80. Bias for magnetic tapes
 In other technique a system of ultrasonic AC bias is
employed, which mixes the audio signal with a high-
frequency signal current
 This bias signal, as it is known, does not get recorded
because the wavelength of the signal is so small that
the magnetic domains resulting from it neutralize
themselves

81. Sound Card
 A sound card is an internal computer expansion card
that facilitates the input and output of audio signals to
and from a computer under control of computer
programs
 Typical uses of sound cards include providing the audio
component for multimedia applications such as music
composition, editing video or
audio, presentation, education and entertainment
(games) and video projection

82. Sound Card
 Typical blocks of a sound card are as below
 ADC
 DAC
 PCI(Peripheral Controller Interface)
 I/O ports
 DSP(Digital Signal Processor)
 Memory

83. Sound Mixers
 A sound mixer is a device which
takes two or more audio signals,
mixes them together and provides
one or more output signals
 As well as combining signals,
mixers allow you to adjust levels,
enhance sound with equalization
and effects, create monitor feeds,
record various mixes, etc

84. Sound Mixers
 Some of the most common uses for sound mixers
include:
 Music studios and live performances: Combining
different instruments into a stereo master mix and
additional monitoring mixes.
 Television studios: Combining sound from
microphones, tape machines and other sources.
 Field shoots: Combining multiple microphones into 2
or 4 channels for easier recording.

85. Sound Mixers
 Input channel controls
 Input Gain / Attenuation: The level of the signal as it enters
the channel. In most cases this will be a pot
(potentiometer) knob which adjusts the level
 Phantom Power: Turns phantom power on or off for the
channel
 Equalization: Most mixers have at least two EQ controls
(high and low frequencies).
 Auxiliary Channels: Auxiliary channels are a way to send a
"copy" of the channel signal somewhere else to provide
separate monitor feeds or to add effects
 Pan & Assignment: Each channel can be panned left or
right on the master mix. Advanced mixers also allow the
channel to be "assigned" in various ways

86. Sound Mixers
 Solo / Mute / PFL: These switches control how the
channel is monitored. They do not affect the actual
output of the channel
 Channel On / Off: Turns the entire channel on or off.
 Slider: The level of the channel signal as it leaves the
channel and heads to the next stage (subgroup or
master mix).

87. PA Systems & Installations
 A public address
system (PA system)
is an electronic
amplification
system with a
mixer, amplifier
and
loudspeakers, used
to reinforce a
sound source

88. Digital Consoles
 Digital Console is an electronic device for combining,
routing, and changing the dynamics of digital audio
samples
 Digital mixing consoles are typically used in recording
studios, public address systems, sound reinforcement
systems, broadcasting, television, and film post-
production

89. Digital Consoles
 Advantages:
 There is no added noise, distortion, or other signal
degradation while the signal is in the digital domain,
between the output of the analog to digital converter
(ADC) and the input to the digital to analog converter
(DAC)
 Aux sends can be mixed on the main faders rather than
on a row of potentiometers
 Signal routing is often much more flexible than with an
analog-based console

90. Digital Consoles
 Advantages:
 The setup of the console can be saved and loaded at will.
This is particularly useful in live events where a setup for
each band can be largely prepared in
advance, saved, and then loaded as needed
 There are typically many on-board effects and virtual
signal processors available, eliminating the need for
additional hardware modules, and the associated
cost, size, weight, cabling, signal quality issues, etc

91. Digital Consoles
 Disadvantages:
 There is an analog to digital conversion, then processing
of the signal, then again digital to analog
conversion, which degrades the sound quality. This is
subject to debate, since the quality degradation is not
always noticeable
 The number of faders is often less than the number of
input channels. The extra input channels are not
accessible until a bank of faders is switched to control
them

92. Digital Consoles
 Disadvantages:
 Digital conversion and processing adds latency, or
delay, into the signal
 The act of making adjustments is often slower for
compact digital mixers which require the user to page
through one or more layers of commands before
reaching the desired control