MicrophonesA microphone (colloquially called a mic or mike; both pronounced / ma kˈ ɪ /) is anacoustic-to-electric transducer or sensor that converts sound into an electrical signal.Microphones are used in many applications such as telephones, tape recorders, karaokesystems, hearing aids, motion picture production, live and recorded audio engineering,FRS radios, megaphones, in radio and television broadcasting and in computers forrecording voice, speech recognition, VoIP, and for non-acoustic purposes such asultrasonic checking or knock sensors.Most microphones today use electromagnetic induction (dynamic microphone),capacitance change (condenser microphone), piezoelectric generation, or light modulationto produce an electrical voltage signal from mechanical vibrationThe history of microphones to modern developmentInventionIn order to speak to larger groups of people, there was a desire to increase the volume ofthe spoken word. The earliest known device to achieve this dates to 600 BC with theinvention of masks with specially designed mouth openings that acoustically augmentedthe voice in amphitheatres. In 1665, the English physicist Robert Hooke was the first toexperiment with a medium other than air with the invention of the "lovers telephone" madeof stretched wire with a cup attached at each end. In 1874, Ernst von Siemens describedthe "dynamic" or "moving-coil" transducer, though the first result of this invention was notthe microphone, but its adaptation in 1920 to make a loudspeaker. During the mid-19thcentury a number of inventors came up with devices that led to the invention of the firstpractical electrical telephone patented by Alexander Graham Bell in 1876.Inventors Emile Berliner and Thomas Edison were inspired to improve this and both wenton to design and build the first carbon microphone (then called transmitter) in mid-1877,within a month of each other. After a long legal dispute, Edison was awarded the patent.Modern development
Jack Brown interviews Humphrey Bogart and Lauren Bacall for broadcast to troopsoverseas during World War II.Edison continued to refine the carbon microphone, which was employed at the first everradio broadcast, a performance at the New York Metropolitan Opera House in 1910. In1916, C. Wente of Bell Labs developed the next breakthrough with the first condensermicrophone.In 1923 the first practical moving coil microphone was built. "The Marconi Skykes" or"magnetophon", developed by Captain H. J. Round, was the standard for BBC studios inLondon. This was improved in 1930 by Blumlein and Holman who released the HB1A andwas the best standard of the day.In the same year, the ribbon microphone was introduced, another electromagnetic type,believed to have been developed by Harry F. Olson, who essentially reverse-engineered aribbon speaker. Over the years these microphones were developed by several companies,most notably RCA that made large advancements in pattern control, to give themicrophone directionality. With television and film technology booming there was demandfor high fidelity microphones and greater directionality. Electro-Voice responded with theirAcademy Award-winning shotgun microphone in 1963.During the second half of 20th century development advanced quickly with the ShureBrothers bringing out the SM58 and SM57. Digital was pioneered by Milab in 1999 with theDM-1001.The latest research developments include the use of fibre optics, lasers andinterferometers. Reference : https://en.wikipedia.org/wiki/MicrophoneHow it worksMicrophones are a type of transducer - a device which converts energy from one form toanother. Microphones convert acoustical energy (sound waves) into electrical energy (theaudio signal).Different types of microphone have different ways of converting energy but they all shareone thing in common: The diaphragm. This is a thin piece of material (such as paper,plastic or aluminium) which vibrates when it is struck by sound waves. In a typical hand-held mic like the one below, the diaphragm is located in the head of the microphone.Location of Microphone Diaphragm
When the diaphragm vibrates, it causes other components in the microphone to vibrate.These vibrations are converted into an electrical current which becomes the audio signal.Note: At the other end of the audio chain, the loudspeaker is also a transducer - it convertsthe electrical energy back into acoustical energy.Types of MicrophoneThere are a number of different types of microphone in common use. The differences canbe divided into two areas:(1) The type of conversion technology they useThis refers to the technical method the mic uses to convert sound into electricity. The mostcommon technologies are dynamic, condenser, ribbon and crystal. Each has advantagesand disadvantages, and each is generally more suited to certain types of application. Thefollowing pages will provide details.(2) The type of application they are designed forSome mics are designed for general use and can be used effectively in many differentsituations. Others are very specialized and are only really useful for their intendedpurpose. Characteristics to look for include directional properties, frequency response andimpedance (more on these later).Mic Level & Line LevelThe electrical current generated by a microphone is very small. Referred to as mic level,this signal is typically measured in millivolts. Before it can be used for anything serious thesignal needs to be amplified, usually to line level (typically 0.5 -2V). Being a stronger andmore robust signal, line level is the standard signal strength used by audio processingequipment and common domestic equipment such as CD players, tape machines, VCRs,etc.This amplification is achieved in one or more of the following ways:• Some microphones have tiny built-in amplifiers which boost the signal to a high miclevel or line level.• The mic can be fed through a small boosting amplifier, often called a line amp.• Sound mixers have small amplifiers in each channel. Attenuators can accommodatemics of varying levels and adjust them all to an even line level.• The audio signal is fed to a power amplifier - a specialised amp which boosts thesignal enough to be fed to loudspeakers.
Refrence:http://www.mediacollege.com/audio/microphones/how-microphones-work.htmlTypes of microphonesLiquid microphoneLiquid microphones, invented by Alexander Graham Bell and Thomas Watson,were among the first working microphones to be developed, and they were aprecursor to what would later become the condenser microphone. Early liquidmicrophones used a metal cup filled with water and sulfuric acid. A diaphragm wasplaced over the cup with a needle on the receiving side of the diaphragm. Soundwaves would cause the needle to move in the water. A small electrical current ran tothe needle, which was modulated by sound vibrations. The liquid microphone wasnever a particularly functional device, but it makes a great science experiment.Carbon microphoneThe oldest and simplest microphone uses carbon dust. This is the technology usedin the first telephones and is still used in some telephones today. The carbon dust
has a thin metal or plastic diaphragm on one side. As sound waves hit thediaphragm, they compress the carbon dust, which changes its resistance. Byrunning a current through the carbon, the changing resistance changes the amountof current that flows.Fiber optic microphoneFiber optic systems, which use super-thin strands of glass to transmit informationinstead of traditional metal wires, have been revolutionizing the field oftelecommunications in recent years, including microphone technology. So whatsthe big deal? Unlike conventional mics, which are often big and send an electricalsignal, fiber optic microphones can be extremely small, and they can be used inelectrically sensitive environments. They can also be produced with no metal, whichmakes them very useful in magnetic resonance imaging applications and othersituations where radio frequency interference is an issue.Dynamic microphones
A dynamic microphone takes advantage of electromagnet effects. When a magnetmoves past a wire (or coil of wire), the magnet induces current to flow in the wire. Ina dynamic microphone, the diaphragm moves either a magnet or a coil when soundwaves hit the diaphragm, and the movement creates a small current.Electret microphoneElectret microphones are among the most widely used microphones on Earth.Because theyre cheap and relatively simple, electret mics are used in cell phones,computers and hands-free headsets. An electret microphone is a type of condensermicrophone in which the external charge is replaced with an electret material, whichby definition is in a permanent state of electric polarization.Ribbon microphones
In a ribbon microphone, a thin ribbon -- usually aluminum, duraluminum or nanofilm-- is suspended in a magnetic field. Sound waves move the ribbon, which changesthe current flowing through it. Ribbon microphones are bidirectional meaning theypick up sounds from both sides of the mic.The RCA PB-31 was one of the first ribbon microphones. It was produced in 1931,and changed the audio and broadcasting industries because it set a new standardwhen it came to clarity. Several other microphone makers made comparablemodels, including the BBC-Marconi Type A and ST&C Coles 4038.Laser microphoneA laser microphone works by capturing vibrations off of a plane, like a windowpane,for example, and transmitting the signal back to a photo detector, which convertsthe reflected laser beam into an audio signal. When sound hits the windowpane, itbends and causes the laser beam to bend, which can be translated to sound usinga photocell. In recent years, scientists have been developing a new type of lasermicrophone that works by streaming smoke across a laser beam thats aimed atphotocell, which is then converted to an audio signal.Carbon microphone
The oldest and simplest microphone uses carbon dust. This is the technology usedin the first telephones, and is still used in some telephones today. The carbon dusthas a thin metal or plastic diaphragm on one side. As sound waves hit thediaphragm, they compress the carbon dust, which changes its resistance. Byrunning a current through the carbon, the changing resistance changes the amountof current that flows.Condenser microphonesA condenser microphone is essentially a capacitor, with one plate of the capacitormoving in response to sound waves. The movement changes the capacitance ofthe capacitor, and these changes are amplified to create a measurable signal.Condenser microphones usually need a small battery to provide voltage across thecapacitor.Crystal microphones
Certain crystals change their electrical properties as they change shape for oneexample of this phenomenon). By attaching a diaphragm to a crystal, the crystal willcreate a signal when sound waves hit the diaphragm.As you can see, just about every technology imaginable has been harnessed toconvert sound waves, into electrical signals. The one thing most have in common isthe diaphragm, which gathers the sound waves and creates movement in whatevertechnology is being used to create the signal.Reference:http://www.howstuffworks.comPolar patterns
A microphones directionality or polar pattern indicates how sensitive it is to soundsarriving at different angles about its central axis. The polar patterns illustratedabove represent the locus of points that produce the same signal level output in themicrophone if a give sound pressure level (SPL) is generated from that point. Howthe physical body of the microphone is oriented relative to the diagrams depends onthe microphone design. For large-membrane microphones such as in the Oktava(pictured above), the upward direction in the polar diagram is usually perpendicularto the microphone body, commonly known as "side fire" or "side address". For smalldiaphragm microphones such as the Shure (also pictured above), it usually extendsfrom the axis of the microphone commonly known as "end fire" or "top/endaddress".