Carbon Microphone

The carbon microphone is not widely used these days. 

The carbon microphone was developed in the 1870s.

 It was the first reliable form of microphone and it was widely used for many years before being supplanted by other types that gave much higher levels of performance.

The basic concept behind the carbon microphone is the fact that when carbon granules are compressed, their resistance decreases. 

This occurs because the granules come into better contact with each other when they are pushed together by the higher pressure.

The carbon microphone comprises carbon granules that are contained within a small container that is covered with a thin metal diaphragm. A battery is also required to cause a current to flow through the microphone.

When sound waves strike the carbon microphone diaphragm it vibrates, exerting a varying pressure onto the carbon. These varying pressure levels are translated into varying levels of resistance, which in turn vary the current passing through the microphone.


The varying current can be passed through a transformer or a capacitor to enable it to be used within a telephone, or by some form of amplifier.
The frequency response of the carbon microphone, however, is limited to a narrow range, and the device produces significant electrical noise. Often the microphone would produce a form of crackling noise which could be eliminated by shaking it or giving it a small sharp knock. This would shake the carbon granules and enable them to produce a more steady current.

Applications

They were widely used in telephone 
Radio

Carbon microphone advantages & disadvantages

As with any form of microphone there are advantages and disadvantages.

Carbon microphone advantages

• High output
• Simple principle & construction
• Cheap and simple to manufacture

Carbon microphone disadvantages

• Very noisy - high background noise and on occasions it would crackle
• Poor frequency response
• Requires battery or other supply for operation



MOVING COIL MICROPHONE: 

Principle: 

A moving coil microphone works on the principle of electromagnetic induction. Whenever a magnet is moved relative to a coil a current is produced in the coil.

Construction and Working

: A moving coil microphone has three main parts: a diaphragm, a moving coil and a permanent magnet. The diaphragm is a thin piece of metal, plastic or aluminium that vibrates when it is struck by sound waves. It is attached to the moving coil, which vibrates in response to the incoming sound waves. That is, the coil moves back and forth around the permanent magnet. This movement is converted into electrical signals, which are directed towards the loudspeaker through the wires.
The moving coil microphone is one of the most widely used forms of free standing microphones. It is widely used for vocals for musical performances as well as for many other applications.
The dynamic microphone is also simple in its design and as a result good microphones offer good value for money.




The dynamic or moving coil microphone relies on the fact that if a wire held within a magnetic field is moved then an electric current is induced. This is the same effect as seen in an electric generator and many other items




The assembly is held in place by an outer casing and the coil can move freely over the magnet.
As sound waves hit the diaphragm, this causes the coil to move backwards and forwards within the magnetic field







Cordless Microphone: 

A wireless microphone, or cordless microphone, is a microphone without a physical cable connecting it directly to the sound recording or amplifying equipment with which it is associated. Also known as a radio microphone, it has a small, battery-powered, radio transmitter in the microphone body, which transmits the audio signal from the microphone by radio waves to a nearby receiver unit, which recovers the audio







A wireless microphone system is made up of the following 3 pieces:

1. Microphone
2. Transmitter
3. Receiver
Practically all wireless microphone systems use FM (frequency modulation) and need roughly 200 kHz bandwidth. 


Loudspeaker:

A loudspeaker is a transducer that converts an electrical audio signal into a corresponding sound. 
There are several different technologies and approaches used within loudspeakers. As a result there are several different types of loudspeaker 

Moving Coil Loudspeaker:

It consists of a cone attached to a coil that is held within a magnetic field. It basically consists of a diaphragm, typically attached to a coil though which the audio is passed.
When a current flows in a wire, a magnetic field appears around it. When the wire is wound into a coil, the effect is increased.
If the coil is placed into a steady magnetic field created by a fixed magnet, then the two magnetic fields will interact. Opposite poles attract and like poles repel. This means that the current flowing in the coil can cause the coil to be attracted or repelled from the fixed magnetic field - the degree of the force being proportional to the current flowing. If the coil is attached to a large diaphragm, then the sound waves will be more effectively transferred to the air.







The coil is suspended within a magnetic field and this means that the variations in current flow resulting from the electrical audio signal cause the coil, and hence the cone to move. This results in the loudspeaker converting the electrical audio signal into sound.





The moving coil loudspeaker is the most widely known and used form of loudspeaker. It can be found in many electronic items from radios to Bluetooth speakers and in public address systems - in fact anywhere that electrical waveforms need to be turned into audible sound.
The whole paper in cone type loudspker acts as a diaphragm and causes pressure variation direct in the listeners area . Hence it is called "Direct radiating type loudspeaker





Horn loudspeaker: 

It uses the same electromagnetic effect as the moving coil loudspeaker, a diaphragm held within a magnetic field that is varied in line with the audio. This causes the diaphragm to vibrate and these vibrations are then magnified by a horn.
The use of Horn loudspeakers can provide higher efficiency and more directionality
The main advantage of horn loudspeakers is they are more efficient; they can typically produce approximately 3 times (10 dB) more sound power than a cone speaker from a given amplifier output.
Therefore, horns are widely used in public address systems, megaphones, and sound systems for large venues like theatres, auditoriums, and sports stadiums







Multispeaker systems 

In order for a speaker to efficiently produce sound, especially at lower frequencies, the speaker driver must be baffled, this generally takes the form of a speaker enclosure or speaker cabinet.




Hi-fi speaker system for home use with three types of dynamic drivers
1. Mid-range driver
2. Tweeter
3. Woofers

Number of speakers tells the way of system. A system having one driver speaker is known as one way system. If it has the three drivers, one to handle h.f, 2nd to handle mid range frequency and 3rd to handle low frequencies then it is called three way system








The smaller drivers capable of reproducing the highest audio frequencies are called tweeters, those for middle frequencies are called mid-range drivers and those for low frequencies are called woofers.


A typical three way system may cover the following frequency ranges:

Low Freq. Range                     30-800Hz                Woofer
Mid frequency range                800 Hz-6KHz           Mid range
HF Range                                 above 6KHz             Tweeter