A microphone is a type of transducer or input devise, which is a device that converts one form of energy into another. A microphone is capturing acoustic energy, the sound waves of a voice or musical instrument and converting it into electrical energy. The electrical energy, or the electrical representation of the sound wave, is then transferred to the next device in the audio chain through the microphone cable or via a wireless system, which sends the audio signal through space using radio waves. There are several types of microphone designs that perform this task using different methods.

In this lesson we will look at two of the most common types of microphones that you will use: Dynamic and Condenser

Watch the video (left) to get a introduction into the differences between a dynamic and a condenser microphone.

Dynamic microphones use an assembly consisting of a thin diaphragm, a voice coil, and a magnet. As sound waves strike the diaphragm, which is usually made of a very thin plastic, it causes the attached voice coil to vibrate within the magnet's field. Dynamic microphones tend to be more resistant to rough handling, humidity, and temperature change. They can also handle extremely loud sounds and are almost impossible to overload. For these reasons, dynamic microphones are widely, though not exclusively, used in live sound reinforcement. They are also very cost effective.

Summary

■ Suitable for vocals, drums and instrument amplifiers.

■ Cardioid polar pattern (pick up pattern) is most common.

■ Needs to be placed close to sound source.

■ Less sensitive and doesn't pick up unwanted ambient room noise.

■ Rugged construction and hard to damage.

■ No phantom power required.

Condenser microphones use an assembly consisting of a diaphragm and an electrically charged back plate. When the condenser element is charged, an electrical field is created between the diaphragm and the back plate. As sound waves strike the diaphragm and causes it to vibrate, the spacing in between the two surfaces varies, affecting the electrical charge in the assembly. This fluctuation creates the electrical representation of the sound wave.

Because of their design, condenser microphones can be considerably more expensive than dynamic microphones. They are also more sensitive to temperature and humidity changes or rough handling. However, condensers provide a great advantage over dynamics in theatre applications for a couple of reasons. First, they can be made much smaller than dynamics, making them much easier to mount on or hide in costuming. Secondly, they generally have much better frequency response and higher sensitivity, making then better for use in critical sound reinforcement applications and better for overhead or boundary microphone techniques where the microphones are placed much further from the performers.

Summary

• They need an external power supply (unlike dynamic)

• Some have battery attachment as part of microphone housing or on the end of the mic cable as part of the connector.

• Others need power delivered to them through the cable of the mixer. This power system is called Phantom Power

• Condenser mics are known for their crisp, responsive sound and they have a wide flat frequency response (they can reproduce a wide range of frequencies evenly and accurately).

• Somewhat sensitive so condensers are often used for more distance placement than dynamic mics.

• Work well for recording vocal and instrumental ensembles from a distance.

• Too sensitive for drums but work well with cymbals because of their wide frequency response.

• Omnidirection polar pattern

Phantom Power is a term given to the process of delivering DC (Direct Current) to microphones requiring electric power to drive active circuitry. Condenser microphones all have active circuitry and require phantom power.

The power can be provided by a battery located inside of the mic. Alternatively (and most commonly) the DC power is provided by the mixer and delivered to the condenser microphone via the mic cable. This method is referred to as phantom power. The worldwide standard for phantom power is 11 to 52 volts of DC (typical studio mics run on 48v). Your preamp will typically have a button labelled 48v, which allows you to turn this on/off. However, some older mixers and cheaper audio interfaces may not have phantom power. In this case, an external phantom power supply can be added between the condenser mic and the preamp.

• Vocals - Dynamic Mic for handheld or a Condenser for choral.

• Drums - Dynamic Mic on Kick, Snare and Toms, Condenser for Cymbals

• Guitar & Bass - Dynamic Mic (Mic the amplifier)

• Horns - Dynamic Mic

• Piano - Two Condensers, one for treble strings and one for lower strings

• Electronic Keyboards - Dynamic (Mic the amplifier)

Lavalier microphones are made of small elements (usually condenser) designed to be mounted with a clip or pin to clothing. They are generally connected to a preamp assembly (what you see attached to the belt of a performer), or for wireless applications, they can be connected to a transmitter. The design of these mics makes them inconspicuous enough to be used in TV broadcast, video production, and of course, theatre. Contemporary designs almost exclusively use condenser elements. They can now be as small as a few millimetres in diameter and weigh only an ounce or so (not including the pre-amp assembly).

Lavaliers allow you to place the microphone much closer to the actor's mouth, increasing gain before feedback. Lavaliers, therefore, allow you to minimise pick up of room noise, stage vibrations and other unwanted sounds. They are also more easily hidden and less cumbersome. When used with wireless systems, they give performers almost unlimited mobility.

A lavalier does a good job of close mic-ing, especially when mounted in front of the ear or on the hairline. However, the ultimate position would be at the performer's mouth. The only way to do this is with a headset microphone. While not quite as discreet as a lavalier, most modem headsets are very lightweight and comfortable for the wearer. Many headsets have a frame that goes over the head but most professional quality headsets have a lightweight wire frame that sits on the ears and wraps around the back of the head, with a short boom arm that holds a condenser element at the comer of the mouth. They are available in various colours so that they can be less obvious to the audience.

All headsets should be stable enough to maintain the microphone position at the mouth regardless of the head movements of the actors. More and more large-scale productions are using headsets, especially in high-energy musical performances.

These capture sound by hanging down from above the stage. Overhead microphones usually are comprised of a condenser element mounted on a short gooseneck, which then leads to a thin cable. The length of cable can be up to 10-15 metres long, and ends in the necessary pre-amplifier assembly.

The main drawback with using overheads is these microphones are further away from the sound source than even a microphone on a floor stand would be and will pick up more ambient sound than preferred. This, in addition to the possibility of these mics actually being closer to loudspeakers than to the sound source, can lead to significantly reduced gain before feedback. They are, however, good if you want to capture a full stage sound such as the chorus of a musical.

Boundary microphones are an alternative to each individual performer have a mic and an alternative to overheads. These microphones are designed to be laid flat on an acoustically reflective surface, in this case the stage itself. Again, these microphones are usually condenser elements in a low profile housing. They would be placed along the lip of the stage, with a unidirectional polar pattern aiming back at the action on stage. They obviously need to be out of the actors' way as far downstage as possible.

The drawbacks to these microphones are some of the same drawbacks we have seen with overhead microphones, primarily the distance from the sound source and the proximity to the loudspeakers. Add to this, the pickup of stage noise from the actors' feet, scenery movements, etc. You can alleviate some stage noise by placing a soft felt or foam pad in between the mic and the stage, and decreasing the low frequencies on the EQ. Small boundary microphones can be hidden in permanent scenery, such as on a table in the centre of a room scene.

A radio mic is a microphone that does not have a lead connected to the handheld microphone (the transmitter). The transmitter sends radio waves (known as RF ie radio frequency) to the receiver which is tuned to the transmitting frequency. The output of the receiver is connected to an audio channel. The transmitter and receiver both require power, the transmitter (ie microphone) via battery, the receiver via mains power. This system allows the speaker or performer to have more mobility as there are no cables. Radio mics can be either dynamic or condenser and can be in the form of handheld, lapel or lavalier and headsets. The lapel and headset both require a body pack transmitter that the speaker or performer carries with them.

Have a quick look at how to mix microphones for live performance but we wil do more of this later on when we are looking at mixing.