Condenser and Dynamic
There are two main types of microphone, "condenser" and "dynamic". Each has a characteristic
sound quality and is suited to particular tasks. Condenser mics are typically used for vocals,
cymbals, and acoustic instruments as they have a more "transparent" sound quality. Dynamics are
traditionally more robust and suited to loud parts such as drums and guitar amps.
When buying a
microphone, you need to consider the benefits of each type and decide which will be better suited
to the job. It helps to know what a microphone sounds like, so it is good to experience different
mics. Often you will not have the opportunity to try a mic before you buy it, so microphone
manufacturers supply graphs and test results that help describe the nature of their microphone.
A dynamic microphone is similar to a speaker, it has a coil attached to a diaphragm which
moves inside a magnetic field. As the coil oscillates in the magnetic field, it generates
a signal ( an electrical current whose voltage fluctuates from positive to negative values ).
A condenser microphone works on the principle of capacitance. 2 conductive plates ( usually gold
plated ) are positioned parallel and charged with a potential difference ( one may be earthed,
the other charged with electrons ). One plate is fixed firmly to the microphone body, the other is allowed to
vibrate freely as the sound waves hit it. As the plates get closer the potential difference
increases, as they part further it decreases. This results in a signal representing the
waveform of the sound that was vibrating the diaphragm.
Condensers are more sensitive to quiet
sounds than Dynamics, but they require "phantom power" to charge the capacitor. Most mixing
desks and many preamps provide phantom power ( 48 volts DC over pins 1 & 2 ), but you must be
sure your preamp can provide it otherwise you cannot use a condenser mic.
Some condenser
mics are battery powered, and we call them "Electret condenser microphones".
Noise is generated by many phenomenae, not least RF interference. This is why it is important
to use sheilded cables. Noise is especially problematic at microphone level, because the signal is
so low that it needs to be amplified twice before it can drive a speaker. Consequently, any
noise in the signal will be amplified and will become audible. Try it yourself: plug your mic
into a preamp and send the signal to a power amp so you can hear it in the speakers - you
will hear a ( hopefully ) quiet hiss.
When looking at microphones, take note of the signal-to-noise
rating, as it is an indication of how much the signal can be amplified before the noise is audible.
You need a very quiet microphone for recording an electric guitar, whereas a noisey microphone
may do a good job of recording a snare. It all comes down to choosing the right mic for the job,
and every good engineer gets to know their microphones.
