Dorset Sound & Communications

Sound system design for the 21st Century

Microphones, Types and Use

There are two types of microphones They are used for two different applications. A dynamic microphone, the larger type with the ball windscreen, uses a diaphragm attached to moving coil of wire suspended around a magnet to produce a small electrical signal. In a condenser or electret microphone, an electrical signal is generated by a capacitor in the element of the microphone. As you speak into a condenser mic the sound wave pressure hits one side of the capacitor and causes it to move closer to the other side of the capacitor, compressing the dielectric (insulator) in between, causing a bias electrical signal to vary. A transistor circuit, in the mic handle or in an inline module, amplifies the signal variations so the mixer can use it. Both types of microphones have their advantages and disadvantages.

Dynamic microphones are very rugged. They are designed to be used by solo vocalists and musical instruments where high sound pressure levels occur.

Dynamic microphones work best when they are used close to the sound source - within about six inches. They are less sensitive and much larger than most condenser type microphones. They are often well shock mounted to stop rustling noise from hand movement. Neodymium and rare earth magnet structures have made possible dynamic mics that approach the sensitivity of some condenser microphones. 

Condenser microphones are used where it is not possible or desirable for the microphone to be close to the sound source. We use condenser microphones on pulpits, suspended over choirs, and on altars. These microphones have the advantage of being much more sensitive than dynamic microphones and as such the source can be farther away from the mic and still be picked up quite well. This helps when you have inexperienced people using the microphones. Condenser mics also work well as clip-on, or lavaliere type microphones. Used in this manner, the microphone does not have to be right up at the person's chin, it can be placed lower down on the user's clothing. Also becoming popular are headset or even earset microphones such as the nearly invisible Countryman E6, Audio Technica AT892 or Galaxy AS-HSA. With the element right at the performers' or pastors' mouth, feedback is almost non-existent, the voice sounds clearer and more natural, and the level never changes with head movement. If you wear a robe and a collar, call us to try one. No more trying to figure out where to clip the mic. After the first five minutes the Janet Jackson/Garth Brooks- look-alike comments end and most users say they will never go back to a clip-on mic. If you get a chance to see one of the PBS Celtic Lady specials you will see that all they use are miniature earset mics (granted, DPA 4066, almost $700/earset without the $8000 wireless system). They are nearly unnoticeable and the sound is spectacular.  All professional grade belt-pack wireless transmitters can be outfitted with head/earset mics

The capacitor element and the interface circuit built into the mic requires electricity to function. This is usually supplied by your mixer power supply and is called phantom power. Phantom power is DC (direct current) 'battery' power that flows back to your mic through the microphone cable. Sound is an AC (alternating current) electricity phenomenon.  At the mic and at the mixer phantom power is filtered out of the audio signal. Most audio mixers today have phantom power built into them as a standard feature. Look for a phantom power switch on your mixer if your electret mics are not working. Some have a switch on each channel. In cases where a mixer used in a sound system does not have phantom power, condenser microphones can be powered from an external phantom power supply or from batteries. Most electrets you will encounter will work with as little as 9 volts. Some studio style mics often called "true condensers" require as much as 52 volts, but most work with the 48 volts  modern mixers supply.

Microphones are either directional or omni-directional (all directions). Directional microphones (also called cardioid for the rounded heart shaped pickup pattern) pick up sound well from one direction and reject it from all other directions. The standard pattern is about 120 degrees wide in front of the microphone. A super- or hypercardioid mic will have a 90 to 100 degree pattern. The "shotgun" mics used most often in news gathering have even tighter patterns. Contrary to common belief, shotguns do not pick up sound from farther away, they just block more of the off axis noise around the mic.  For the most part, directional mics are used in sound reinforcement systems to reduce the possibility of feedback. Directional microphones exhibit what is called proximity effect. The closer you get to the head of the mic, the bassier and gutsier the sound becomes*. Some singers and rockin' preachers really like the effect and have come to count on it to project "their" sound. The only exception are the ElectroVoice RE15 and RE20 "single-D" designed microphones. 

Omni-directional microphones pick up sound evenly from all around the mic element.Omni-directional microphones are best suited for sound recording systems where they are useful for picking up both the direct sound and the effect of the room. They make lousy stereo mics because they pick up everything and don't develop the audible directional cues that create a stereo image. The tonal sound of an omni is usually more natural. Because they pick up equally as well from the behind and in front of the element, they are more susceptible to feedback and discouraged in reinforcement systems. The only place we use omnidirectional microphones are clip-on or earset wireless microphones.  Feedback is less of a concern because they are much closer to the mouth, lack of proximity effect makes them sound more natural, they exhibit much less cable rubbing noise and head turning causes much less level variation.

*Who knows it those are words. They ought to be.

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