There are many different types of microphone in common use. The differences are usually described in two ways: The technology they use (e.g. dynamic, condenser, etc) and their directionality (e.g. omnidirectional, cardioid, etc). In addition, microphones have a number of other characteristics which need to be taken into account.

When choosing a microphone, the first thing you will need to know is what characteristics you need. After that, you can worry about things like size, brand, cost, etc. Note: If you haven't done so already, you might like to do some groundwork and read how microphones work first.

Directionality

Decide which type of directional pattern best fits your needs. Usually it's better to use a less directional mic in a position close to the sound source, than to be further away using a hypercardioid. For more information see microphone directional characteristics.

Frequency Response

You need to be sure the mic's frequency response is appropriate for the intended use. As a rule of thumb, flat response patterns are the very best- however sometimes a tailored response curve for the microphone will be even better if the microphone is for a single purpose, such as singing or instrument pickup. For more information see microphone frequency response CLICK HERE.

Impedance

The rule of thumb is: Low impedance is better than high impedance. For more information see microphone impedance.

Handling Noise

A microphones diaphragm works by converting vibration from sound waves into electrical signals. Unless the microphone has some sort of protection system, the diapragm can't tell the difference between a desirable sound wave vibration and or other sort of vibration (such as a person dropping the microphone or tapping on its side case). All sorts of vibration will be included in the audio signal coming out of the microphone.

If your microphone will possibly be subjected to handling noise or vibration, you should find a microphone which will significantly reduce or or even prevent this noise from being picked up and added to your audio signal. High quality hand-held mics usually attempt to isolate the diaphragm from vibrations using foam padding, suspension, or some other method. Lower quality mics tend to easily transfer vibrations from the casing right into the diaphragm, resulting in a a horribly noisy recording or live sound system.

Interestingly - lavalier mics usually don't have any protection at all from handling noise, primarily because they are too small to incorporate any padding. That alone makes it quite important to make sure they will neither be be moved, bumped or handled in any way.

Best Priactices - Purchasing a New Microphone

If possible, it's always best to buy a range of microphones and use the most appropriate one for each job. If your budget is limited, consider all the different things you need to use the mic for and find microphones which will do a reasonable job of as many of them as possible.

• For vocalists, consider a simple cardioid dynamic mic (such as the Sure SM58) for an all purpose well rounded microphone.
• For video teams or news gathering, a useful option is a condenser mic with selectable directionality, so you can change between cardioid and hypercardioid. If you can afford three mics, consider a hand-held dynamic, a shotgun condenser, and a lapel mic.

To Compare...

In the end, what constitutes "good sound" is in the ears of the beholder. Choose the microphones that you like the sound of. But hopefully you now have a good starting point for considering the options and either eliminating or including microphones some by specification and type alone.

Microphones, like speakers are a type of transducer - a device which converts energy from one form to another. Microphones convert acoustic energy (sound/audio waves) into electrical energy which then makes the audio signal.

Different types of microphone will have different ways of converting energy, however they all have one thing in common: a diaphragm. This is a thin piece of material (such as paper, plastic or aluminium) which vibrates when in the presence of sound waves. In a typical hand-held mic, the diaphragm is located at the head or top of the microphone.

Microphone Diaphragm

When a diaphragm vibrates, it causes other components in the microphone to also vibrate. These sympathetic vibrations are converted into an electrical current which then becomes what we refer to as the audio signal.

Note: At the other end of the audio chain, the loudspeaker is also a transducer - it converts the electrical energy back into acoustical energy (moves air for sound waves).

Types of Microphone

There are a number of different types of microphone in common use. The differences can be divided into two types:

1. The type of conversion technology they use
   This is the the technical method the mic uses to convert sound into electricity. The most common technologies are dynamic, condenser, ribbon and crystal. Each has advantages and disadvantages, and each is generally more suited to certain types of application.
2. The type of application they are designed for
   Some mics are designed for general use and can be used well in many different situations. Other microphones are quite specialized and are only really suited for their intended purpose. Characteristics to look for include directional properties, frequency response and impedance.

Mic Level & Line Level

The electrical current generated by a microphone is very small. Referred to as mic level, this signal is typically measured in millivolts. Before it can be used for anything serious the signal needs to be amplified, usually to line level (typically 0.5 -2V). Microphones "preamplified" to line level may now have their signal added to various processing equipment or line level mixers - similar to the signal strewngth that comes from a DVD payer or a CD player.

This amplification is achieved in one or more of the following ways:

* Some microphones have tiny built-in amplifiers which boost the signal to a high mic level or line level. * The mic can be fed through a small boosting amplifier, often called a line amp or a preamp. * Sound mixers have small amplifiers in each channel. Attenuators can accommodate mics of varying levels and adjust them all to an even line level. * The audio signal is connected to a power amplifier - a specialized amp which boosts the signal enough to then connect to loudspeakers.

Dynamic microphones are versatile and ideal for general-purpose use. They use a simple design with few moving parts. They are relatively sturdy and resistant in nature to rough handling. They are also better suited to handling high volume levels, such as from certain musical instruments or amplifiers. They have no internal amplifier and do not require batteries or external power.

How a Dynamic Microphone Works

When a magnet is moved near a coil of wire an electrical current is generated in the wire. This is the electromagnet principle that a dynamic microphone uses a wire coil and magnet to create the audio signal.

The diaphragm is attached to a coil inside the microphone case. When the diaphragm vibrates in response to incoming audio / sound waves, the coil moves backwards and forwards past the magnet. This creates a small current in the coil which is then channeled from the microphone using wires aka micropone cable.

Dynamic Microphone

All loudspeakers perform the opposite function of microphones by converting electrical energy into sound waves. This is demonstrated perfectly in the dynamic microphone which is basically a loudspeaker in reverse. When you look at a cross-section of a speaker you will notice the similarity with the diagram above. If fact, some intercom systems use the speaker as a microphone.

Technical Notes:

Dynamics do not usually have the same flat frequency response as condensers. Instead they tend to have a specific frequency response for particular applications.

Neodymium magnets are more powerful than conventional magnets, meaning that neodymium microphones can be made smaller, with more linear frequency response and higher output level.

Condenser means capacitor, an electronic component which stores energy in the form of an electrostatic field. The term condenser is actually obsolete but has stuck as the name for this type of microphone, which uses a capacitor to convert acoustical energy into electrical energy.

Condenser microphones require power from a battery or external source. The resulting audio signal is stronger signal than that from a dynamic. Condensers are also usually more sensitive and responsive than dynamics, making them well-suited to capturing subtle nuances in a sound. They are not ideal for high-volume work, as their sensitivity makes them prone to distort.

How Condenser Microphones Work

A capacitor has two plates with a voltage between them. In the condenser mic, one of these plates is made of very light material and acts as the diaphragm. The diaphragm vibrates when struck by sound waves, changing the distance between the two plates and therefore changing the capacitance. Specifically, when the plates are closer together, capacitance increases and a charge current occurs. When the plates are further apart, the capacitance decreases and a discharge current occurs.

A voltage is required across the capacitor for this to work. This voltage is supplied either by a battery in the mic or by external power, also known as "phantom power".

Condenser Microphone

The Electret Condenser Microphone

The electret condenser mic uses a special capacitor which has a permanent voltage built in during it's manufacture. This is similar in principle to permanent magnet, in that it doesn't require any external power for operation. However good electret condenders mics usually include a pre-amplifier which does still will require that there be power at that stage.

Other than this difference, you can think of an electret condenser microphone as being the same as a normal condenser.

Technical Notes:

• Condenser microphones have a flatter frequency response than dynamics.
• A condenser mic works in much the same way as an electrostatic tweeter (although obviously in reverse).

Every microphone has a property known as directionality. This describes the microphone's sensitivity to sound from various directions. Some microphones pick up sound equally from all directions, others pick up sound only from one direction or a particular combination of directions. The types of directionality are divided into three main categories:

1. Omnidirectional Picks up sound evenly from all directions (omni means "all" or "every").
2. Unidirectional Picks up sound predominantly from one direction. This includes cardioid and hypercardioid microphones.
3. Bidirectional Picks up sound from two opposite directions.

To understand a the directional properties of particular microphones, user manuals, written specifiactions and promotional material often include a graphical representation of the microphone's directionality. This graph is called a polar pattern. Some typical examples are shown below.

Omnidirectional

Omnidirectional Captures sound equally from all directions.

Uses: Capturing ambient noise; Situations where sound is coming from many directions; Situations where the mic position must remain fixed while the sound source is moving.

Notes:

* Although omnidirectional mics are very useful in the right situation, picking up sound from every direction is not usually what you need. Omni sound is very general and unfocused - if you are trying to capture sound from a particular subject or area it is likely to be overwhelmed by other noise.

Cardioid

CardioidCardioid means "heart-shaped", which is the type of pick-up pattern these mics use. Sound is picked up mostly from the front, but to a lesser extent the sides as well.

Uses: Emphasising sound from the direction the mic is pointed whilst leaving some latitude for mic movement and ambient noise.

Notes:

• The cardioid is a very versatile microphone, ideal for general use. Handheld mics are usually cardioid. * There are many variations of the cardioid pattern (such as the hypercardioid below).

Hypercardioid

Hypercardioid Hypercardiod microphones are very directional and eliminates most sound from the sides and rear, due to their long thin design. Hypercardioids are often referred to as "shotgun microphones".

Uses: Isolating the sound from a subject or direction when there is a lot of ambient noise; Picking up sound from a subject at a distance.

Notes:

• By removing all the ambient noise, unidirectional sound can sometimes be a little unnatural. It may help to add a discreet audio bed from another mic (i.e. constant background noise at a low level). * You need to be careful to keep the sound consistent. If the mic doesn't stay pointed at the subject you will no longer be able to pick up the audio. * Shotguns can have an area of increased sensitivity directly to the rear.

Bidirectional

Bidirectional Uses a figure-of-eight pattern and picks up sound equally from two opposite directions.

Uses: As you can imagine, there aren't a lot of situations which require this polar pattern. One possibility would be an interview with two people facing each other (with the mic between them).

Variable Directionality

These microphones allow you to vary the directional characteristics by selecting omni, cardioid or shotgun patterns.

This feature is many times found on video camera microphones, with the purpose that you can adjust the directionality to suit the angle of zoom, e.g. have a shotgun mic for long zooms. Some models can even automatically follow the lens zoom angle so the directionality changes from cardioid to shotgun as you zoom the camera in.

Although this seems like a good idea (and can sometimes be handy), variable zoom microphones don't perform particularly well and they often make a noise while zooming. Using different mics will usually produce better results.