Followers

Recent

Theme images by Storman. Powered by Blogger.

Recent in Sports

Home Ads

Comments

Ads

Random Posts

Search This Blog

Popular

Pages

Monday, 30 August 2021

Types of Telephone System

- No comments

TYPES OF TELEPHONE SYSTEM


Telephone systems were primarily designed to deliver a human speech (voice). They are also utilized for data transmission. A modem is used to transfer data. The telephone network that connects the two consumers is known as the public telephone network (PTN). Because PTN links consumers via one or more switches, it is also known as a public telephone network (PSTN).


Public switched telephone network (PSTN)


The switching centers in the public switched telephone network are classified into five types, as shown in Figure. They are namely:


1. Regional offices (class1)

2. Sectional offices (class2)

3. Primary offices (class3)

4. Toll offices (class4)

5. End offices (class5)

Figure:   PSTN Hierarchy

The customer's phone is linked to the terminal (or central office) through a local loop. The terminal office is linked to one toll office. Several toll offices are linked to the headquarters. Several major offices are linked to divisional offices. Several division offices are linked to a single district office.


Phones are used to utilize rotary or pulse dialing. In the system, a digital signal is delivered to the terminal office for each number dialed. This sort of selection results in a selection mistake due to human error. The touch-tone method is being used to make calls. Instead of digital transmission, the user transmits two short bursts of the analog signal in this approach. The sent signal's frequency is determined by the row and column of the pad pushed. A 12-tone dialing system with push buttons is shown in the image. When a user dials the number 5, for example, the terminal receives two bursts of analog signals with frequencies of 770 and 1336Hz. The Touch-Tone dialing system is,

 

 

1209 Hz

1336 Hz

1477 Hz

1663 Hz

697 Hz

1

2

3

A

770 Hz

4

5

6

B

852 Hz

7

8

9

C

941 Hz

*

0

#

D

 

Electronic switching system


The figure shows a simplified schematic demonstrating how two telephone sets (subscribers) are interconnected via a central office dial switch. Each subscriber is linked to the switch through a local loop. The switch is an electronic switching mechanism (ESS machine). Local loops are terminated at the calling and called stations in telephone sets, as well as at the central office ends to switch machines.

Figure: Electronic Switching System

When the calling party's telephone set releases the hook (i.e. pulls the mobile phone out of the holder), the switch hook on the telephone set is released, resolving the DC channel between the tip and the loop ring through the microphone. The ESS machine detects DC current in the loop and recognizes it as a state of the hook. Because the loop is completed through the telephone, this technique is known as the loop start operation.


INTEGRATED SERVICES DIGITAL NETWORK (ISDN)


The data and telephone communications business is continuously evolving to suit the demands of telephone, video, and computer communications systems. More individuals are communicating with one another than ever before. To satisfy this need, previous standards are updated daily, while new standards are established and deployed regularly.  A hypothetical network developed by major telephone companies to offer worldwide telecommunications support for voice, data, video, and fax information inside the same network is known as an Integrated Services Digital Network (ISDN). ISDN is the combination of several services into a single multipurpose network. ISDN is a network that allows an unlimited number of independent users to be connected over the same communication network.


Principles of ISDN


The capacity to handle various voice (telephone) and non-speech (digital data) applications in the same network utilizing a variety of standard facilities is an essential aspect of the ISDN concept. ISDN is compatible with a wide range of applications, including switched and unmodified (dedicated) connections. ISDN's fundamental concept is a digital connection at 64 kbps. Customers connect to the ISDN system via a local interface that is linked to a digital transmission medium known as a digital pipeline. Depending on the customer's needs, several tube diameters are available with varying capacity (i.e. bit rates). A home client, for example, may just want a minimal capacity to contain a phone and a personal computer. Office complexes, on the other hand, may necessitate conduits with adequate capacity to handle a big number of interconnected digital telephones via private branch exchanges (PBXs) or a high number of computers on a local area network (LAN).


ISDN Architecture


The figure shows the block diagram of the ISDN function architecture. The ISDN network is intended to accommodate the customer's completely new physical connection. There are several protocols available that allow control information to be sent between the customer's device and the ISDN network. ISDN channels may be divided into three kinds. They are namely:


1) B channel: 64 Kbps

2) D channel: 16 Kbps or 64 Kbps                       

3) H channel: 384 Kbps, 1536 Kbps, 1920 Kbps

Figure: ISDN Architecture

According to ISDN standards, home network customers are given three full-duplex, time-division multiplexed digital channels, two running at 64 Kbps (called B channels, forbearer) and one at 16 Kbps (designated as D channel, for data). The D channel is used for signaling and sharing network control information. One B channel is utilized for digitally encoded audio and the other for data transfer.


The 2B+D service is known as the basic rate interface (BRI). BRI systems require bandwidth that can support two 64 Kbps B channels, one 16 Kbps D channel, and additional special bits. As a result, the overall bit rate of BRI is 192 Kbps.


Features of ISDN


The features of ISDN are given below


1) ISDN can handle a large range of voice (telephone) and non-voice (digital data) applications on the same network by utilizing a small number of defined facilities.


2) ISDN connections can be switched or non-switched (dedicated).


3) An ISDN will have intelligence for delivering service features, maintenance, and network management tasks.


4) The 64-Kbps digital link is the foundation of ISDN. New ISDN services should be compatible with 64 Kbps switched digital connections.


5) OSI (open system interconnection) standards can be utilized for ISDN.


6) Depending on national regulations, ISDN can be deployed in a variety of ways.


VIDEOPHONES


Videophones work on the same concept as television transmission and reception. Voice communication takes place via a radio connection in the UHF band. A (camera) pick-up tube detects the scene. The video signal from the camera pick-up tube is amplitude modulated. The voice signal from the phone is frequency modulated. The relative position of picture and sound carrier frequencies stays the same as in a traditional TV system. If the channel bandwidth ranges from a to b MHz, the image carrier = (a+1.25)MHz and the sound carrier = (b-0.25) MHz. Solid-state image sensors are utilized to capture the figure/scene. An LCD screen is used to show information.


The communication takes place through via:


1. Coaxial cable links

2. Microwave space communication

3. Satellite communication

Figure: Video Phone

The figure shows a schematic block diagram of a videophone system. The picture signal from the camera is amplified and sent to a modulation amplifier, where it is amplitude modulated and mixed with the modulated frequency, the audio signal, and sent to the antenna transmission. When a user dials a number for an outbound call, the dial pulse creates a tone, and the call is routed through the switched telephone network. Modulated tones are transmitted. When a call is received at the destination, the called party will 'release' their hand. At that point, the transmitter is ACTIVE, and the acknowledgment signal is returned to the call control terminal with a 2150 Hz tone. However, after the video recognition signal is received, the speech merging network is activated at both ends, and the amplitude modulated picture is merged with the frequency-modulated speech and delivered down a common axis.


This establishes an audio/video link between the person calling and the person being called. After the image, the voice is separated on the video detector at the end of the discussion, and when the conversation is concluded, the combined network is turned off. These video phones are commonly utilized as a way of communication between industries, businesses, research institutes, and huge organizations.

Friday, 27 August 2021

Radar and Navigational Aids

- No comments

RADAR AND NAVIGATIONAL AIDS


RADAR


Radar is a device that uses radio waves to track distant objects. The main aim of radar is to determine: whether there are objects in the region to be searched, the distance between the radar and the object, and the speed of the object as needed. Navigation aids are devices that assist vehicles to navigate in areas where signage is not available, such as at sea or in the air.


Radar- fundamentals


RADAR stands for RAdio Detection And Ranging. It consists of a transmitter and a receiver, both of which are linked to a directional antenna. The transmitter sends an Ultra High Frequency (UHF) or Microwave signal, while the receiver measures the echo signal returned from the target. When a pulsed signal is utilised in a transmitter, the distance between the transmitter and the target is estimated by calculating the time it takes for the signal to reach the receiver. If a continuous wave is utilised in the transmitter, the target's speed and direction of movement are estimated by detecting the signal frequency difference, which is known as the Doppler effect.

Basic Radar System


Figure shows a pulsed radar block diagram. It is made of a transmitter and a receiver, both of which are linked by a directional antenna. Through an antenna, the transmitter may send out UHF or big microwaves.


The receiver absorbs as much energy as possible from the target's echo, analyses the incoming signal, and displays it appropriately. The receiving antenna and the transmitting antenna are the same. Since radio energy is released in pulses, this is accomplished using a type of time-division multiplexing. The pulse is sent via the antenna. After some time, the echo signal or signal reflected by the object reaches the antenna. Because of the time delay, the time allocation approach is utilized to use the same antenna for transmission and reception. 


Applications 


• The primary applications of radar include, but are not limited to, target search in open space or at sea, target tracking to follow target trajectory, and aircraft height readings. 


• Radar may be utilised as a navigation aid in a variety of ways. It has a wide range of military applications. Radar technology in aeroplanes can offer important navigational information. Radar equipment aboard ships gives information on land masses, other ships, and so on. 


• Radar is used in the military to deliver armaments to ships, planes, and direct missiles, among other things. Furthermore, radar is useful for aiding aeroplane landings, monitoring air traffic at airports, and allowing aircraft to fly above the ground.


Radar range equation


The reflected signal power that reaches the RADAR Receiver diminishes as the distance between the RADAR Transmitter and the target increases. The RADAR Receiver will be able to handle a certain amount of detectable power. The minimum power determines the greatest distance between the RADAR and the target, also known as the RADAR's Maximum Range. When the received power equals the receiver's lowest received power Pmin, the maximum range Rmax is reached. Rmax represents the maximum range. The equation of maximum range Rmax can be given as:

Where Pt = Peak value of the transmitted pulse power.

A0 = capture area of the receiving antenna.

S = Effective cross-section area of the Target (Also known as Radar cross-section)

Pmin = minimum received power

λ = wavelength of the transmitted signal


Factors influencing Maximum Range


The radar equation is given by

1. As per the above equation, the maximum range is proportional to the fourth root of the peak transmitted pulse power. To double the maximum range, the peak power must be raised 16 times while maintaining all other factors unchanged in the calculation. Such an increase in electricity is too costly.


2. A decrease in minimum receivable power has the same impact as increasing transmitting power and is thus a highly appealing alternative to it.


3. The radar range equation also demonstrates that the maximum range is proportional to the square root of the antenna's capture area, and hence exactly related to its diameter. To double a given maximum radar range, the effective width of the antenna must be doubled.


4. Increasing the frequency can also raise the Rmax. There is a limit to increasing frequency. An antenna's beamwidth is related to the wavelength/antenna diameter ratio. As a result, every increase in the diameter to wavelength ratio will result in a narrower beam.


Finally, the radar equation demonstrates that the maximum radar range is affected by the target area.


The basic pulsed radar system


A typical high power pulsed radar system is represented in Figure. The modulator is supplied with rectangular voltage pulses by the trigger source. This voltage pulse is utilized as the output tube's supply voltage, switching it on and off.

Pulsed Radar Block Diagram

Microwave oscillators or amplifiers like klystrons, travel wave tubes, or cross-fields can be used in these tubes. The radar transmitter section is finished with a duplexer, which sends the output pulse to the antenna for transmission.


When no transmission is occurring, the receiver is linked to the antenna. A duplexer is used for this. In the receiver, the mixer is the initial step. It produces little noise. The primary receiver advantage is provided at frequencies of 30 or 60 MHz. The IF amplifier is tuned to the same frequency and has the same bandwidth characteristics as the RF amplifier. Finally, the detector is a Schottky blocking diode, the output of which is amplified by the same video amplifier as the IF amplifier. After that, the output is sent to the display unit. A cathode-ray tube is the most common type of display device.


Display methods


A radar receiver's output can be represented in various ways. The three most popular methods are as follows.

They are:

i) A scope

ii) Plan Position Indicator (PPI)

iii) Direct feeding to a computer

Separate displays may provide additional information such as height, speed, or velocity.


A Scope display


The display device works in the same way as a cathode ray oscilloscope. Sweep waveforms are employed on horizontal deflection plates of cathode ray tubes (CRTs). The beam steadily travels from left to right across the CRT screen before returning to its original place.


If no signal is received, the display in scope display A is a horizontal line. The demodulation receiver's output is sent to a vertical deflector plate, which causes the beam in the display to travel vertically, as seen in the figure.

 

The target distance is represented by the displacement from the CRT's left side. The initial 'blip' is created by a transmitted pulse. The other blip is a reflection from a nearby item, followed by a sound. Different targets then appear as big fixtures. The height of each beep correlates to the strength of the returned echo, while the distance from the reference bar is a measure of the distance.


Scope performance is great for tracking since only echoes coming from one direction are visible.


Plan Position Indicator (PPI)


• The timing wave of the sawtooth deflects the point of the cathode ray dramatically off-centre in this situation, therefore plan position indications are most often employed for this type of intensity modulation. It is timed with the sent pulse.


• The distance out from the centre of the display is proportionate to the target distance of the radar transmitter's echo production.


• The angular direction of the sawtooth beam location shows the orientation of the antenna beam.


The signal from the receiver output is applied to the control electrode of the cathode ray tube. The bias voltage at the control electrode is adjusted slightly higher than the cut-off voltage.


As a result, a signal with a high amplitude activates the spot. As a consequence, the target's echo shows as a bright spot with the target's distance and azimuth in polar coordinates. PPI screens are utilised in search radar and are especially useful when cone scanning is employed.


Automatic target detection


Manual radar performance might be inconsistent or incorrect. For example, the radar receiver's output is processed in a computer system before it is presented on the radar screen. Analogue computers can also be utilised to receive and analyse data, as well as for automated tracking and missile indications. A computer calculates the object's distance from the radar and speed based on the reflected signal and displays it on a monitor without the need for human interaction. These systems are referred to as automatic target detection systems since they function without human involvement.


NAVIGATIONAL AIDS


Radar may be used to help navigation in a variety of ways. It has several military applications. Radar technology in aeroplanes can give valuable navigational information. Radar equipment aboard ships gives data on land masses, other ships, and so on.


Radar is used in the military to deliver weapons to ships, planes, and direct missiles, among other things. Furthermore, radar is useful for helping aircraft landings, monitoring air traffic at airports, and enabling aircraft height above the ground.


Aircraft landing systems


One of the most significant elements influencing the dependability of air travel is the ability to land an aircraft in poor or no visibility circumstances. Two electronic systems are typically utilised for aeroplane landing systems. They are:


(i) Instrument Landing System(ILS)

(ii) Ground Controlled Approach(GCA)


Both of these configurations are blind approach systems. The final landing is typically performed visually after the electronics system has brought the aircraft out of the overcast in the proper position to execute a landing.


Instrument Landing System (ILS)


Figure shows the key components of the instrument landing system, which include a runway finding device, skateboard equipment, and a marking beacon.


Runway localization offers lateral guidance, allowing the aircraft to approach the runway in the proper direction. They are made up of a polarised bidirectionally polarised high-frequency radio network. A set of equations is derived using this radio network, as illustrated in the picture. 1.5. The track location's range differs from that of a long wave radio network.

Instrument Landing System

The radiated wave in the runway localizer is composed of a single carrier wave. The carrier wave is concurrently amplitude modulated at 90 and 150 Hertz.


The two patterns in figure correspond to the relative intensities of the 90 and 150 Hertz sidebands as a function of direction. The equi-signal course directions are therefore represented by equality in the intensities of the two modulations. In the receiver output, suitable filters separate the two modulated signals, which are then individually rectified and applied with opposite polarity to a zero-centre metre. As a result, metre deflection is absent when tone amplitudes are equal. If the tone intensity of the two signals differs, the stronger signal will deflect the pointer in a direction that indicates the direction in which the aircraft should fly to "correct" its flight.

Directional Pattern of Localizer and Glide Path in ILS.

Marker beacons are used to indicate position along the localizer route, as seen in figure. They are made up of low-power extremely high-frequency transmitters that excite antenna systems. This antenna arrangement generates fan-shaped beams. The beams are directed so that the wide dimension of the fan is perpendicular to the localizer route. Tone modulations and dot-and-dash keying are used to distinguish the various markers.


The glide-path equipment offers equi-signal path guidance in the vertical plane, comparable to the equi-signal path guidance in azimuth given by the localizer. The ideal gliding angle is between 2 and 5 degrees.


The glide path signal receiver isolates the two modulation tones, which are then rectified and applied to a zero-centre metre with opposite polarity.


This indicator is typically coupled with the localizer indication by housing the two-metre movements in a common casing in such a way that the localizer and glide-path pointers are vertical and horizontal when not deflected, respectively. Thus, any flight adjustments necessary to maintain the set courses in both the vertical and horizontal planes may be achieved with a fast glance at the one-meter face.


Ground Controlled Approach (GCA)


Two radars are used in the ground control approach system. The first is for general observation and to monitor aircraft traffic patterns around the landing strip. The second is a high-resolution short-range kit that is intended to practise landings. This second radar has two displays: one that shows elevation as a vertical displacement and rotates as a horizontal displacement, and the other that shows azimuth on the PPI indicator. The first display shows the matching glide path. The second display indicates the approach direction. The aircraft to be landed using this method is first brought into position using surveillance radar before beginning its descent. The controller on the high-resolution radar set indicator then takes over and occasionally informs the pilot on what needs to be done to ensure the aircraft is on the intended glide path. As a result, the aeroplane is "discussed" on a route that corresponds to the right landing, so that when the clouds breakthrough, it is in the correct position to visually complete the landing.


If the aircraft cannot be guided to the proper glide for whatever reason, it is commanded to abort the landing and return for a second attempt.


Advantage of GCA


The ground-controlled approach method has the benefit of requiring no equipment onboard the aircraft other than a standard radio receiver and allowing the ground installation to be transportable.


Dis-advantage of GCA


One of the drawbacks is that the network contains a lot of human links.

Wednesday, 25 August 2021

Microphones - Types, Advantages and Disadvantages

- No comments

MICROPHONES - TYPES, THEIR ADVANTAGES AND DISADVANTAGES:


We can define a  microphone as "an electro-acoustic transducer that transforms sound waves into varying electrical currents". There are two types of microphones. They are namely:


i) Pressure Microphone and

ii) Pressure Gradient Microphone


i) Pressure Microphone


In pressure microphones, acoustic pressure operates on just one side of the moving element in pressure microphones, and the output is proportionate to the pressure applied to the moving element.


Examples of pressure microphones are:


1. Carbon Microphone

2. Condenser Microphone

3. Piezo - Electric Microphone and

4. Moving Coil Microphone


ii) Pressure Gradient Microphone


The acoustic pressure acts on two sides of the moving element in pressure gradient microphones, and the resultant output is proportional to the difference in pressure acting on the two sides of the moving element. Example: Velocity Ribbon Microphone.


A. CARBON MICROPHONE:


A carbon microphone is a small container packed with carbon grains known as a carbon button. The button is in continuous contact with a thin steel diaphragm through an electrode known as the plunger. When no sound waves contact the diaphragm, the resistance of the carbon button stays constant. When sound waves contact the diaphragm, it displaces and the plunger linked to it changes the pressure exerted to the carbon button. As a result, the resistance of the carbon button varies.

Figure 1 Simple Carbon Microphone

The figure illustrates a carbon microphone diagram. The carbon button is connected to a dc power source. A dc voltage source is linked in series with the carbon button. As a result, the sound waves change the circuit current in response to changes in resistance.


Applications:


1. It's prevalent in telephones.

2. It can be effectively employed in radio communications.


Advantages are:


1. Electrical output is high.

2. Cost-effective.

3. It is sturdy (strong).


Disadvantages: 


1. Low-frequency response

2. Lack of faithfulness.

3. It makes a lot of noise when it operates.


B. CONDENSER OR CAPACITOR MICROPHONE:


A condenser microphone relies on capacitance, which changes between a fixed plate and a tightly stretched metal diaphragm to operate. It is made up of two extremely thin plates, one of which is moveable and the other one is fixed. A capacitor is made up of these two plates. Since it was originally known as a condenser, it is now known as a condenser microphone. The diaphragm, or moving plate, is separated from the fixed plate by a short distance.

Figure 2 Condenser Microphone

Between the plates, a polarising voltage (Eo) is applied. The figure shows a condenser microphone. When a sound wave impacts the diaphragm, it displaces the diaphragm and alters the distance between the two plates, which affects the capacitance of the microphone.


Applications:


1. Used as the principal standard in calibration.

2. Used to record high-quality sound.


Advantages are:


1. Extensive frequency response

2. Minimal distortion

3. Extremely compact.

4. Good signal-to-noise ratio (S/N).


Disadvantages:


1. Because of its high internal impedance, it necessitates the use of a built-in pre-amplifier.

2. A polarising voltage of 200 to 400 volts is required.

3. Produces a small Output.


C. PIEZO-ELECTRIC MICROPHONE (OR) CRYSTAL MICROPHONE:


A crystal microphone operates based on the ‘Piezoelectric Effect,' which is described as the ‘difference in potential between the opposite sides of particular crystals created when they are exposed to mechanical pressure.' A crystal microphone is made up of a Bimorph, which is just two crystals linked in series or parallel. If the crystals are linked in series, the output result is in the form of voltage. The parallel connection has a lower internal impedance. A driving pin connects one end of the bimorph to the diaphragm's center. The figure shows the schematic diagram of this microphone.

Figure 3 Diaphragm Actuated Crystal Microphone

When sound waves get in touch with the diaphragm, variable pressure is delivered to the crystal through the connecting pin, and changing voltage is created between the plates.


Applications:


1. In a public address system.

2. Found in hearing aids.

3. Found in sound level meters.


Advantages:


1. High sensitivity.

2. The frequency response is good.

3. Low cost.

4. Small size.

5. It is a non-directional microphone.

6. Produces a lot of production.

7. A polarised source is not required.


Disadvantages:


1. Influenced by temperature and humidity.

2. High mechanical impedance of its vibrating components.

3. Not appropriate for hot regions since the crystal loses its piezoelectric characteristics.


D. MOVING COIL (OR) ELECTRODYNAMIC MICROPHONE


A moving coil microphone is made out of a tiny wire coil that is held in high magnetic fields and rigidly connected to the back of the diaphragm. The diaphragm is corrugated to increase its strength and mobility. The figure depicts a moving coil or electrodynamic microphone.

Figure: Moving Coil Microphone

When sound waves hit the diaphragm, it travels back and forth, dragging the coil along with it. The coil's motion cuts the magnetic lines of force and produces an alternating current voltage in the coil. The frequency of the alternating current voltage is the same as the frequency of sound waves. The amplitude of this voltage is proportional to the air pressure of the sound waves.


Application:


1. Used for recording systems both indoors and outdoors.


Advantages:


1. There is a low internal impedance.

2. Constant frequency response

3. It does not require any external power.

4. It is lightweight.

5. Unaffected by mechanical vibration, temperature, or moisture.


Disadvantages are: 


1. The open-circuit voltage sensitivity is low.


E. VELOCITY RIBBON OR PRESSURE GRADIENT MICROPHONE:


The velocity ribbon microphone operates on the pressure gradient principle, which states that the driving force exerted on a moving element is proportionate to the difference in pressures acting on its two sides. The figure depicts a velocity ribbon microphone.

Figure: Velocity Ribbon Microphone

It is made up of a light corrugated metallic ribbon hung between the magnetic pole components n and s, which is open to sonic stresses on both sides. The resulting driving power is proportional to the pressure differential between the diaphragm's two sides (Ribbon). This construction is installed in a circular baffle with radius l, which defines the length of the air route between the two sides of the ribbon. When a sound wave strikes the ribbon, it travels back and forth in proportion to the sound's velocity. It causes a voltage to be generated in the ribbon by cutting the force lines between the magnet's poles. This voltage is relatively low, however, it may be raised with a transformer.


The word ‘directivity' in a microphone refers to how much signal it receives from each direction, ranging from 0 to 3600. The bi-directional feature of a velocity ribbon microphone is depicted in the Figure below. The bi-directional microphone receives the strongest signal between 00 and 1800 and no signal between 900 and 2700.

Figure: Bi-Directional Characteristics of Velocity Ribbon Microphone

 


Application:


1. Applicable for studio works.


Advantages:


1. Better frequency response than moving coil type.


Disadvantages:


1. It requires a built-in transformer due to its low internal impedance.

Monday, 16 August 2021

Direct Radiating and Horn Loudspeaker

- No comments

LOUDSPEAKER:


An electro-acoustic transducer, or loudspeaker, is a device that transforms electrical signals into sound signals. In sound reproduction, loudspeakers are devices that transform electrical energy into acoustic signal energy and broadcast it in a room or open air. The term "signal energy" refers to electrical energy that has a defined form, such as speech, music, or other audible signals (about 20 to 20,000 hertz).


CHARACTERISTICS OF AN IDEAL LOUDSPEAKER:


1. Electro acoustic efficiency is close to 100%.

2. Over the entire audible range, the acoustic output is frequency independent.

3. The output is free of harmonics and inter-modulation distortion.

4. The input signal is accurately replicated.

5. It can emit a non-directional radiation pattern.

6. It must be compact and provide the necessary acoustic output.


TYPES OF LOUDSPEAKER:


There are mainly three different types of loudspeakers.

They are namely:

1. Dynamic cone-type moving coil loudspeaker.

2. Horn-type moving coil loudspeaker.

3. Electrostatic type loudspeaker.


A. DYNAMIC CONE TYPE MOVING COIL (OR) DIRECT RADIATOR (OR) ELECTRODYNAMICS LOUDSPEAKER:


It is based on the fact that when a current-carrying conductor is put in a magnetic field, the conductor induces a force.


Construction: Figure 1 shows the structural features of a direct radiator speaker, a dynamic speaker, and a moving coil speaker.


Permanent magnets: A soft iron frame that creates a piece of the pole and a powerful permanent magnet make up the magnetic structure. It's utilized in the annular air gap to provide a high flux density.

Figure: Electromagnetic Loud Speaker

Voice coil (or) speech coil: The coil is wound around a cylindrical shape that is retained in the magnetic structure's annular air gap.


Spider: The voice coil is kept centered by the spring action of the corrugated spider mount.


Diaphragm (cone): It's a paper cone connected to the voice coil that compresses and expands the air in front of the speaker in alternating directions. The corrugations provide appropriate movement flexibility. Similarly, corrugated paper usually known as a spider is used to place the coil end of the cone so that it may easily travel in the gap.


Baffle: A large flat board with a hole in the center through which a cone may operate is the most basic type of baffle.


Dust cap: It keeps dust out of the space between the voice coil and the magnet.


Operation: The voice coil conducts a voice frequency electrical current. A force is created between the coil and the permanent magnet when a positive current is supplied through it, which pushes the coil axially away from the pole structure. It is lightly regulated by the spring action of a corrugated spider structure, which keeps the spool centered. When the current is reversed, the magnetic force is reversed as well, pulling the coil back towards the pole structure.


The air in front of the cone is compressed as the cone moves forward, due to a rarefaction that fits behind it. When the cone travels backward, the procedure is reversed. If all that's left is the cone, the compressed air in front of it can travel back to the cone's edge, where the pressure is low. This maintains normal air pressure in front of the cone. The amount of noise produced is much decreased in this situation. Because the gap between consecutive compression and the then rarefaction is considerable, the loss in sound production is particularly high at low frequencies.


With the use of a blocker, this impact can be minimized. Backward-moving baffles restrict sound waves from entering the cone from the front. As a result, baffles boost low-frequency radiation. Low-frequency radiation is improved by a wider blocking region.

Figure: Frequency Response Characteristics

The figure illustrates the frequency response curve. The magnetic field force, coil size, and effectiveness of the acoustical coupling of the cone all influence the voice coil's ac load impedance measured at the terminals.


The typical range of values is 1 to 300 Ω, with 4, 8, and 16 Ω speakers being the most frequent. The power rating varies between a few milliwatts and several hundred watts. Portable receivers employ lower-power speakers, whereas outdoor auditoriums employ higher-power speakers.


Application:


This can be used in all audio systems


Advantages:


1. It's small and inexpensive.

2. Improved audio range responsiveness.


Disadvantages:


1. Low-frequency efficiency is poor.

2. Directivity pattern with a narrow range of possibilities.

3. The ability to handle a large amount of energy is limited.


B. HORN TYPE LOUDSPEAKER:


At low frequencies, attaching a properly designed horn to a tiny piston line sound source can improve sound production. The speaker's cone is utilized to increase the coupling efficiency between the coil motion and the surrounding air. When the output from a speaker unit is fed into the throat of an acoustical horn, the efficiency increases. The horn functions as both an impedance transformer and a radiator. The construction of a horn-type loudspeaker is explained in the figure.

Figure: Horn Type Loud Speaker

Construction:


A moving coil made up of a former one and a thin aluminum ribbon is coiled into the annular air gap of a hefty permanent pot magnet. The movement of the edge has been designed. With the horn baffle, this driver unit is utilized. The construction of the driver unit is similar to that of a cone-type speaker, with the exception that the cone is not there. Because an unfurled horn might be as long as 2 meters and 1 meter across the mouth, the horn construction is filled back on itself to save physical space.


Working:


Horn acts as an impedance matching device, connecting a high-impedance diaphragm to low-impedance air. A high pass filter is an exponential horn. When the speaker's output is channeled into a horn's throat, the efficiency increases. A longhorn with a smaller taper and a wider area is needed for effective reproduction. These devices can handle more than 100 watts of power with an input impedance of 8 to 16 Ω. The efficiency of horn-loaded loudspeakers is considerably better than that of cone-type loudspeakers.


Application:


1. The main application is: it can be used in Announcement systems.

 


DIFFERENCE BETWEEN CONE AND HORN TYPE LOUDSPEAKER:


S.NO

CONE TYPE LOUDSPEAKER

HORN TYPE LOUDSPEAKER

1

From a few milliwatts to several hundred watts, power handling capability varies.

More than 100 watts of power may be handled by the device.

 

2

Cone loudspeakers are less efficient at low frequencies.

Horn-type speakers are more efficient at low frequencies.

3

Not so

The horn acts as an acoustic transformer, converting low-amplitude diaphragm pressure vibrations into high-amplitude low-pressure vibrations.

4

The size of the diaphragm is larger.

The size of the diaphragm is small.

5

This speaker has a low sound impact.

This speaker has a powerful and effective sound impact.

6

It necessitates the use of an impedance matching circuit external to the system.

It's an impedance matching circuit in and of itself.

7

To cover different octaves of the sound spectrum, several loudspeakers are necessary.

For many octaves of the sound spectrum, one loudspeaker is sufficient.