Building Blocks 21:Mic Technique 4

Mic Technique pt 4: Microphones

Microphone is a generic term that is used to refer to any element which transforms acoustic energy (sound) into electrical energy (the audio signal).  A microphone is therefore one type from a larger class of elements called transducers – devices that translate one form of energy into another form.”*  This is why we also categorize mics as input transducers.

As I mentioned previously, microphones have several characteristics that affect their sound.  This wide variety of microphones allows us to better choose a mic for a particular application.  I will cover some characteristics of mics, but if you want to find a high end quality mic, your best bet is to look for reviews.  Consider what applications you will be using this mic for.  Recording for example is very different than general gaming.  While you can certainly use an inexpensive mic for both applications (I do), if you desire you can get a mic (or three) to tailor to specific uses.

The type of microphone, or rather how a microphone works determines several of its characteristics.  The most common the of microphone is a dynamic mic.  Dynamic mic uses a flexibly-mounted diaphragm and a wire coil in conjunction with a magnet.  The diaphragm reacts to sound by vibrating, which in turn moves the coil back and forth in the magnetic field generating an electrical current.  The physical nature of these mics make them very dependable, durable and fairly insensitive to environmental factors (such as humidity).  The technology is also well developed and capable of making high quality mics.  You can find dynamic mics being used in a wide variety of applications including sound reinforcement (especially outdoors) and recording.

A condenser mic uses a gold-coated diaphragm and a conductive backing plate separated by an air gap to create a condenser (a capacitor).  These mics require a polarizing current of 9-48 volts to be applied to the diaphragm via an external source (phantom power on a sound board provides 48 volts).  When the diaphragm vibrates in response to sound the back plate creates a fluctuating voltage.  Because this voltage is very low, an amplifier is required to drive the signal.  Condensers are able to respond very quickly and accurately to incident sound because they have fewer moving parts (they lack the coil that a dynamic mic has), which also allows them to be smaller than dynamic mics.  They are however more sensitive to physical damage and environmental factors.  Because of this they are generally found in recording and less so in sound reinforcement.

Electret condensers are a special variety of condenser mics.  Their diaphragms are made from a special material that allows the manufacturers to give them a static charge that can be retained indefinitely.  This eliminates the need for a polarizing charge, but an amplifier is still required (between 1.5 and 9 volts).  Electret condensers can be made very small and their necessary power can easily be achieved with batteries allowing for some very unique close miking techniques (theatre and news casting for instance).  This technology is also relatively inexpensive making it a popular choice for consumer products.

Microphones can also be designed with certain functional intentions in mind.  Handheld mics for example are built to isolate handling noise and physical vibration whereas a mic designed to be stand mounted does not need to take this into consideration.  Lavaliers are designed to be worn on a person’s clothing and are built to pic up sound close and all around while a shotgun mic is designed to pick up sound very directionally and sometimes over long distances.

If you’d like to read more on these subjects I recommend Sound Reinforcement Handbook by Gary Davis & Ralph Jones.  Much of the content here is covered in Chapters 10.1 and 10.2

* – Sound Reinforcement Handbook by Gary Davis & Ralph Jones p 113

Comment (1)

  1. Cordovan

    After using a mixing board and mic setup for my computer, it’s hard to go back to a headset! For me, I use a basic analog four-channel mixing board going into (and out of) the computer, and plug a Shure SM57 into the board. Great for Skype, gaming, and podcasting/broadcasting. I’m a bit hardcore when it comes to audio though. 🙂

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