There are many different kinds of microphones, including carbon, ribbon, optical fibre and piezoelectric among others, but the ones that will interest us the most for video work are dynamic and condenser types.
Dynamic microphones use electromagnetic induction to generate an electrical current. A diaphragm is connected to a coil of wire, mounted around a magnet. Changes in air pressure (sound) moves the diaphragm, which moves the coil back and forth around the magnet, inducing an electrical current. Moving coil microphones are functionally the opposite of a loudspeaker. Unlike conenser
microphones, dynamic mics do not need a power source.
Dynamic microphones are relatively inexpensive, moisture resistant and robust, making them suitable for live sound gigs. Often favoured by live bands are the Sure SM57 and SM58 microphones.
Below: Sure SM58 dynamic – a great live gig handheld microphone.
Condenser microphones use the principle of electrical capacitance. (Capacitors used to be known as condensers). As the air pressure changes with the sound, the diaphragm moves accordingly and the electrical capacitance in the microphone also changes resulting in an audio signal. Unlike dynamic microphones, condenser and electret condenser variations must have a power source – either
an internal battery, or external ‘phantom power’ sent down the microphone cable from whatever equipment the microphone is connected to, such as a P.A. mixer or suitably equipped video camera. Typically phantom power is 12 or 48 volts.
Condenser microphones can be made relatively cheaply and are widely used in applications including mobile phones, PC multimedia and headset microphones. Higher quality versions are used for video ‘shotgun’ and lavalier lapel type microphones. Lavaliers are named after a type of pendant jewellery made famous by the Duchess de la Vallière, a mistress of King Louis XIV of France. Lavalier
pendants were worn in similar fashion to the lavalier lapel microphone.
Below left: Popular for video production, Sennheiser K6 condenser base unit with ME66 shotgun attachment. The battery and plug socket is housed in the K6 unit, and will also accept phantom power from a suitably equipped camera or field audio mixer.
Below right: K6/ME66 inside pistol grip and fluffy wind shield. Grip can be screwed onto the end of a boom pole. RØDE microphones refer to their fluffies as ‘dead cats’! This microphone is designed for use with ‘balanced audio’ equipped cameras with XLR connectors. For more info, see the AVTUTES Resources section page Audio Connectors and Adapters
Below: RØDE K2 studio condenser microphone. This mic offers various sensitivity patterns, all selectable by a multi-position switch on the mic. This is a very high quality vocal and instrument microphone, popular in recording studios.
Microphone sensitivity patterns
Various types of microphones are more sensitive than others and respond differently to various frequencies.
A big difference between microphone types is their pattern of sensitivity, in terms of whether they are most sensitive towards the front, sides or rear.
Omnidirectional – sensitive all around the microphone. OK for collecting ambient sound from alldirections, but sound is general, unfocused and may contain unwanted noise.
Bidirectional – equally picks up sound from both sides in a figure 8 pattern. Not a lot of uses, but could suit an interview situation between two people, with the mic sitting between them.
Cardioid – ‘heart shaped’ sensitivity pattern. Sound picked up mostly from the front, but still allowing for some ambient sound from the sides and to a lesser extent, the rear. Handheld mics are usually cardioid.
Hypercardioid – (or ‘supercardioid’) exaggerated cardioid pattern. Very directional towards the front, eliminating most sound from the sides and rear. Hypercardioid mics are often referred to as shotgun mics.
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Below: RØDE Videomic Pro – a condenser hypercardioid shotgun mic designed to be mounted on DSLR and video cameras that only have a 3.5mm external mic socket. Requires a 9V alkaline battery. More info here.
Below: RØDE Podcaster. This is a cardioid pattern dynamic mic with a built in analogue to digital converter, outputting digital audio via USB. The USB connection also powers the A/D converter. The mic also has a built in headphone socket and can be mounted in a suspension cage to minimise mechanical noise such as bumping, which otherwise may be transmitted through the microphone stand. This mic is good for studio use including voiceover and podcasting applications. More info here.
Below: The USB microphone which was supplied as part of the AVID Vocal Studio. Like the Podcaster, this cardioid mic has a headphone socket and connects to a computer via USB. The Vocal Studio came with the M-Audio brand microphone and Pro Tools SE audio software for PC and Mac. Like the Rode Podcaster, this mic is also good for studio use including music, voiceover and podcasting applications.