Microphones

Microphones

Types

There are 4 basic types of microphones: Dynamic, electret, condenser and ribbon.

 

Dynamic Microphones are the most commonly used in live performances and are used in some applications in the studio, such as recording drums or other loud instruments. A dynamic microphone uses magnetic energy to pass the signal to the mixing board. It is actually the reverse of a speaker. Both dynamic microphones and speakers can actually be used interchangeably, but doing so won’t produce the intended quality because they weren’t intended for that purpose.

 

Electret Microphones use a capacitor instead of a magnet. This capacitor is fed into an internal preamp that is charged with battery power and is similar to the condenser mic. Electret microphones are used mostly on acoustic instruments and softer instruments because they are more sensitive than dynamic microphones and pick up much more in the recording process. Although some people may use electret microphones live on stage, they are primarily used in the studio.

 

Condenser Microphones have a capacitor like the electret. However, the condenser mic doesn’t have batteries like the electret. It’s signal is fed to an external mic preamp or phantom power supply, which is usually built into the studio’s mixing board. Condensers are used in the same capacity as the electret, but are of much higher quality and are more expensive than most electrets.

 

Ribbon Microphones are the most fragile of all microphones. They contain a ribbon instead of a capacitor or magnet and are used in special applications where extreme clarity at low volumes is required.

 

Microphone polar patterns

All microphones have a polar pattern. Some of the more expensive mics have switch able multiple polar patterns. Polar patterns are grouped into 3 categories: Omni-directional, Uni-directional, and Bi-directional.

 

Omni-Directional mics have only one polar pattern: Omni. This means that it picks up equally as well from any direction. This is used when you want to record multiple instruments at one time in different positions within the room. For instance, 5 instruments or vocalists could form a circle around an omni-directional microphone and the mic could be facing any direction. As long as the diaphragm, capacitor or ribbon is an equal distance from all instruments, it should pick up everything at equal volume.

 

Bi-Directional mics also have one polar pattern: Figure 8. This type of pattern is used when you want to record two instruments at the same time with one microphone. If you imagine a figure 8, the loops of the 8 are where the mic picks up the most and where the line crosses on the 8 is where it picks up the least. So you can stick one microphone between two instruments and have it pick up equally on each side and reject any sound that comes in off axis where the line of the 8 crosses. Figure 8 microphones are handy for micing the top of a snare and bottom of a hi-hat at the same time or a kick drum and bottom of a snare.

 

Uni-Directional microphones have 3 different polar patterns: Cardioid, supercardioid, and hypercardioid.

 

Cardioid
Cardio means heart. A microphone with a cardioid pattern has a heart shaped pattern. Picture a valentine heart. At the bottom where the heart comes to a point, that is called the on-axis point. This is where the most amount of sound is allowed to enter. As you begin to move off axis to either side, less sound is allowed to enter the microphone. When you move the the back (the top of the heart where the “cheeks” of the heart come together), the least amount of sound is permitted to enter.

 

This type of mic is used most often in multiple micing situations where you want the sound at the back of the mic to be rejected. Although used in studios, cardioid mics are most commonly used in live performances. They are preferred by bands because of their inexpensive pricing and because sound entering from the rear is rejected. This works well with on-stage monitors because the singer can hear himself, yet the mic won’t pick up much of the monitor to cause feedback.

 

Supercardioid
Picture a narrower heart with a hernia bulging at the point where the cheeks come together. On-axis is the point where the most sound is permitted to pass through. As you move off axis to either side, you begin to get some rejection….a little more than with a cardioid. When the sound moves directly behind the mic (180 degrees off axis), more of the sound is permitted to pass through the mic than on the sides, but less than on axis. The best rejection occurs not directly behind the mic, but about 60 degrees from the back of the mic in either direction. Therefore, if you are using an on-stage monitor, the best place to position the monitor is about 60 degrees in front of you instead of directly in front of you.

 

Hypercardioid
Also referred to as a “shot gun” pattern.  Until recently, these were among the most expensive of microphones. But now you can buy them for less than some cardioid microphones. The hypercardioid only picks up in one direction. On-axis. The more you move off axis, the more sound is rejected. Very little sound can come in through the sides, and virtually no sound comes in through the back.

 

This type of mic is used in movie and TV studios where things are mic’d from a distance so you can’t see the microphone on camera. The pattern has to be tight to avoid picking up unwanted sounds off to the side. They also come in handy in the recording studio when you are using multiple mics and need to keep everything as isolated as possible. They are ideal for on-stage performances because you can get a large amount of volume out of them before they begin to feed back.  The cheaper hypercardioid mics have wider patterns, but are still good for on stage. The tighter the pattern you get from one of these, the more you will pay for one.

 

Bass roll off

Some of the more expensive cardioid microphones have in addition to multiple polar patterns (switchable), a bass roll off switch. All three cardioid pattern microphones have a characteristic called “Proximity Effect”. This means the closer you get to the microphone, the more bass is boosted on your sound. In some situations, such as with vocals, this is desirable, and if worked properly, can make your voice sound fuller and punchier when you sing with feel.  However, if you are close-micing a guitar amp, you want the recorded sound to be what the amp is producing. This is where the bass roll-off switch comes in. You can roll off the bass frequencies that produce the proximity effect and you will cause the microphone to record with a more “flat” sound, rather than with that bass boost.

 

Attenuation pad

Another feature of some of the more expensive microphones is an attenuation pad. “Attenuating” a signal means letting less of it pass through. Most mixing boards have an attenuation pad dial to control the amount of signal that comes into the mixer’s input to prevent overloading the input, which causes distortion.  However, if a microphone is overloaded and distorts, it doesn’t matter how much you attenuate the mixer input signal. You will still get distortion.

 

 Most dynamic microphones are hard to overload, so they don’t usually have an attenuation pad switch. But condensers and electrets do overload easily when placed at high sound pressure levels, such as a kick drum, snare, bass amp or guitar amp. When the mic goes into overload and begins to distort, you can switch on the attenuation pad to prevent overload. Some mics will have as many as three levels of attenuation measured in db (decibels [units of measure for sound pressure levels or volume levels]). These levels are usually 3, 6 and 12 db.

 

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