MICROPHONE BASICS
There are many different types of microphones each type is suitable for a different job.
Dynamic microphones:
A Dynamic or moving coil microphone works in exactly the opposite way to a loudspeaker.
A sound wave hits the thin membrane causing it to move backwards and forwards in a
magnetic field. This movement causes an electrical current to flow inside the coil. This current
can then be amplified to a useable level by a simple pre-amp. The microphone is omni
directional which means it responds to sounds from all directions.
There are several advantages for using dynamic microphones:
They are relatively cheap and easy to manufacture.
They require no power supply.
They can tolerate extremely high sound levels.
They are very rugged.
Dynamic microphones do have their disadvantages though.
The movement of the membrane is restricted by the mass of the coil which means an
accurate reproduction of high frequency sounds is poor. In tests it has been showed that the microphone works effectively up to frequencies of about 16kHz. The current generated is so
small that when amplifying a quiet sound the result is unacceptably noisy.
Ribbon microphones
A ribbon microphone works in a similar way to the dynamic microphone except that the coil and
membrane is replaced by a thin conductive ribbon. The ribbon vibrates when a sound wave hits it
causing a voltage to be generated across the ribbon. This small voltage is amplified to a useable
level using a transformer. A good ribbon microphone operates in excess of 20kHz but only responds
to sounds from in front or behind i.e. it is bi-directional. The ribbon can be very fragile which means
that they are not often used in live performances. A ribbon microphone is generally used to record
classical music because it provides a smoother sound than many capacitor or dynamic microphones.
Condenser microphones
A condenser microphone has two electrically charge plates. The sound wave causes the thin membrane to vibrate which alters the capacitance of the two plates. This change in capacitance
can be converted to a voltage which can then be used for recording.
One of the drawbacks of using a capacitor microphone is that a separate 48V power supply is
needed for operation. The main advantage is that the membrane can be made very thin which means excellent frequency response. Another advantage is that they can be made with any kind of response, omni-directional bi-directional etc.
In a traditional system the microphones are all attached to a large mixing desk.
Traditional mixing desks can be very large and expensive.
The main reason why mixing desks are this size is to accommodate the number of
different sound controllers per channel. With a digital studio, microphones are connected to analog to
digital converters and then by optical fiber to the digital signal processor (mixer) The use of a
digital system allows for a virtual mixing desk which encompasses all the features of a traditional
analog mixing desk but can be operated using a simple point and click windows system.
Many traditional sound engineers are opposed to this method as it lacks the feel of a physical system.
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