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Input TransducersInput Transducers

(Microphones)

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MicrophonesMicrophones

Transducers that convert sound waves into electrical signals

There are several different type of microphonesDynamicCondensingCarbon granule

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DynamicDynamic

The diaphragm is moved by changing sound pressure

This moves the coil, which causes current to flow as lines of flux from the magnet are cut

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DynamicDynamic

Advantages Rugged Inexpensive to manufactureTolerates extremely high sound

pressure levels Requires no power supply

DisadvantagesReduced high frequency performanceNeeds amplification

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CondensingCondensing

A pair of parallel metal plates separated by an insulator across which is stored an electrical charge

Q=CV Moving the plates will

change the voltage across them causing current to flow in or out of the capacitor through the resistor

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Charging the Condensing Mic

Charging the Condensing Mic

The microphone must have some means of charging the platesBattery Phantom poweringElectret

The majority of serious recording work is carried out with capacitor microphones

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CondensingCondensing

Advantages No coil and the diaphragm can be

made very thin (few microns thick) thus light weight and less inertia so better high frequency response.

Capacitor microphones can be made with virtually any response pattern.

Disadvantages More complex thus more expensive

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Carbon GranuleCarbon Granule

When acoustical pressure is exerted on the carbon granules, the granules are pressed closer together which decreases the measured resistance.

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Pickup PatternsPickup Patterns

Microphones can also be classified by their pick up patterns Omnidirectional UnidirectionalBidirectional

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OmnidirectionalOmnidirectional

Pickup of sound equally well within a 360 degree radius around the microphone element

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OmnidirectionalOmnidirectional

Advantages Doesn't have to held directly in front of

sound source to pick up adequate sound Gives a sense of the environment Is not affected by slight changes in mic-

to-source distance Provides a natural sound in rooms with

good acoustics Is less susceptible to handling noise and

noise created by wind or popping Is not subject to the proximity effect

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OmnidirectionalOmnidirectional

Disadvantages Difficult to use in noisy locations Susceptible to feedback in

locations where microphone is feeding a loudspeaker

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Unidirectional (Cardioid)Unidirectional (Cardioid)

Primary pickup of sound from one side of the microphone's element Wide angle cardioid Supercardioid Hypercardioid

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UnidirectionalUnidirectional

Advantages Discriminates against

unwanted sound Reduces danger of

feedback in locations where microphone is feeding a loudspeaker

Picks up very little or no background sounds

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UnidirectionalUnidirectional

Disadvantages May be subject to the proximity effect Must be set correctly to avoid sound

source being off-mic Less natural sound in rooms with good

acoustics Must take care to avoid covering ports More susceptible to wind, popping and

handling noises

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BidirectionalBidirectional

Optimum pickup of sound from two sides of the microphone elementAdvantage - can be used to

reduce number of mics in a circuit when two voices are involved in an interview or performing a voice-over

Disadvantage - no separate control over levels of talent, so they must maintain proper mic-to-source distance and remain on-mic

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Proximity EffectProximity Effect

The closer the sound source is to the microphone, the greater the emphasis on the bass frequencies in the sound

Many microphones are equipped with a bass roll-off switch to nullify the proximity effect

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Condenser Frequency Response

Condenser Frequency Response

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Dynamic Frequency Response

Dynamic Frequency Response

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ImpedanceImpedance

One important characteristic of a microphone is its output impedance

This is a measurement of the AC resistance looking back into the microphoneLow (50-1,000 ohms)High (5,000+ ohms)

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Low ImpedanceLow Impedance

Most microphones used in broadcast applications are wired for low-impedance circuits Low-impedance circuits

have three wire connectors: a shield and two other wires (hot and cold) to conduct the current

                               

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Balanced SystemsBalanced Systems

Balanced lines are much less susceptible to RFI (Radio Frequency Interference) and the pickup of the other electrical noise and hum

In a balanced line, the shield of the cable is connected to ground, and the audio signal appears across the two inner wires which are not connected to ground

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Balanced SystemsBalanced Systems

Output signal is split into two opposite phasesPositive and Negative or Hot and ColdWhen returned to the same phase at the

amplifier input noise is cancelled.

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Phantom PoweringPhantom Powering

The standard power supply for microphones is 48v

DC power is supplied along the signal leads, which means no extra cables

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ConnectorsConnectors

Two types of connectors are commonly used with balanced systems

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High ImpedanceHigh Impedance

High-impedance circuits have two wire connectors: a shield and one inner wireUsed in budget systemsHigh impedance makes the signal more

susceptible to electromagnetic interference

Signal is affected by cable capacitance in long runs of cables

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FeedbackFeedback

Feedback occurs when the sound from the loudspeaker arrives at the microphone as loud or louder than the sound arriving directly from the original sound source (talker, singer, etc.)

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Microphones and Stereo Signals

Microphones and Stereo Signals

Coincident or XY pairRight hand microphone

picks up sound form left stage and visa a versa

No phase problems as minimal space between microphones

Sound source

Cardioid Microphones

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FinFin

Fin