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Article ED00009: Choosing the right microphone

Summary:

A practical guide to mic types and uses. Selecting the right microphone for the task can make a huge difference to the quality of your sound.

Application:

Students and educators involved in choosing, using and/or studying microphones for live sound reinforcement and PA, theatre and/or recording situations.

Details:

The microphone is the first component in the sound system chain... a critical item since it is the microphone that picks up the original sound and converts it into an electrical signal ready for amplification and processing.

Basic microphone types

There are two common types of microphones... Dynamic and Condenser. There are others (such as ribbon) but these two are by far the most used in both live sound reinforcement (or PA) and recording applications.

Dynamic mics are generally more robust and considerably less sensitive than condenser mics. This means that you normally use a dynamic microphone very close to the sound source. They also have different frequency response characteristics which is why you would choose a different mic for say a vocalist compared to miking an instrument. Dynamic mics generally can handle very high sound pressure levels... such as close to a snare drum or a guitar amp speaker.
 
Condenser mics on the other hand are typically used further from the source and usually have a much smoother frequency response than dynamic mics. This makes them very suitable for acoustic instruments, choirs and studio recording of vocals (where they are typically used at least 15cm from the singer’s mouth). They also require a power source to operate... either a battery, or most professional condensers use what is known as Phantom Power and is supplied from the mixer via the mic cable.

So now for some “rules of thumb”

Note that “rules of thumb” are just that... not absolute rules for every situation. However you will do well to follow these rules in most cases.
Thumb Rule #1 ... use dynamic mics for close miking, condensers for more distant.
Thumb Rule #2 ... use dynamic mics for louder sound sources (such as very close to brass/wind instruments, drums and amplifiers ... and individual vocalists).
Thumb Rule #3 ... use condenser mics for acoustic instruments and choral groups (such as overhead on drums and percussion, brass/wind sections and strings, pianos, acoustic guitars etc as well as choirs).
 

Lets look a little closer at mic characteristics

Regardless of the construction type (dynamic or condenser) all microphones are designed to have a particular pickup pattern. Broadly speaking they are either directional or non-directional. That is they pick up more sound from a particular direction or they pick up sound from every direction.
 
Most mics used in live PA applications are directional. This is to minimise feedback that would occur if they picked up too much sound from the main speakers or foldback. But just how directional they are is determined by their design. Directional characteristics are shown as polar patterns or pickup diagrams, often also pictured on the mic itself. Of course they are actually 3D.
 
Cardioid and OmniCardioid pattern ... most common and looks like a heart shape. The line shows the level of sound pickup in a circle around the mic. The 0° mark is directly in front of the mic (ie “on axis”), the 180° mark is behind the mic and 90° and 270° is either side (& above/below). As you can see from the cardioid pattern, the mic is most sensitive to sound directly “on axis” then drops off either side and very rapidly as you approach the back. Cardioid mics, when used closely, deliver a noticeable increase in bass response... called the proximity effect. This can be used to great effect for vocals and is an important part of learning mike technique.
 
Omni ... or non-directional. Picks up sound equally from all angles. An ideal mic for recording in the middle of a group of people, such as at a conference table (including live video conferencing). In this case you would use an omni condenser mic due to the pickup distance.
 
Super and Hyper CardioidsSuper Cardioid ... a narrower or more directional pickup pattern than a cardioid, but also has a small pickup from the rear of the mic.
 
Hyper Cardioid ... narrower again compared to a super cardioid mic. It also has a narrow but increased pickup from the rear. Often used for mid distance miking in theatre/drama and choral groups.
 
Lobar ... this is a pattern used with “shotgun” mics indicating very narrow pickup, but also has a significant very narrow pickup from the rear. The pattern looks like narrow lobes, hence the name. Shotguns are also sometimes referred to as super cardioid shotgun (short) or hyper cardioid shotgun (long) because the pattern shapes are similar to super cardioid and hyper cardioid, but much narrower.
 
Bidirectional or Figure 8Lobar patternFigure Eight ... bidirectional pickup (ie in two opposite directions, but minimal at the sides. Useful for some recording applications (such as vocalists facing each other into the one mic) and in a stereo miking setup when combined with a cardioid mic (called Mid-Side miking).
 
Thumb Rule #4 ... Use a cardioid or super cardioid dynamic mic for close live vocals. (Note however that there are some high quality cardioid condensers designed for this use... such as the Sennheiser E865).
Thumb Rule #5 ... For live sound, fewer mics is best, especially when miking from a distance. More open mics = more likelihood of feedback, especially with more sensitive condenser mics.
Thumb Rule #6 ... The further your mic is from the sound source the narrower the pickup pattern needs to be.
Thumb Rule #7 ... Use directional mics for live sound and ensure that you minimise pickup of sound from the main PA and foldback speakers. Eg. the back of a cardioid mic should face the foldback speakers and the main speakers, generally, should be in front of performers and/or at a reasonable distance from microphones.
Thumb Rule #8 ... When holding a directional mic DO NOT cover any of the holes or grill with your hand. This changes the pickup pattern and usually makes it less directional (or omni). This will INCREASE the chances of feedback.

See also:

Miking up your choir

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