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Quick Guide To Microphones

What's the best kind of microphone to use? And what's the difference between the different types? We explain how to choose the best mic for you.

Like many aspects of recording, choosing a microphone is as much black art as science. We can, however, greatly simplify the choice by looking at the two main aspects of a mic - microphone type and microphone pickup patterns.

There are two main types of microphone (although there are other derivations and variations which we'll touch on) and three main responses or pickup patterns. We'll look at the microphone types first.

How microphones work

Most mics work in essentially the same way. They have within them some light material called a diaphragm. When sound waves hit the diaphragm it vibrates generating an electrical current (the audio signal in electronic format) which is then fed to an amplifier, mixer or recording device. The main difference between microphone types is the diaphragm and how it generates the electrical signals.

Dynamic mics

The diaphragm in dynamic microphones consists of a thin membrane, usually plastic or metal, attached to a coil of wire which sits inside a magnetic field. The field may be generated by a magnet inside the coil or surrounding it. When sound waves hit the diaphragm it moves the coil in and out of the magnetic field generating electrical impulses. For this reason these mics are sometimes known as moving-coil mics.

The diaphragm and coil are usually quite sturdy (compared to other mic types) which makes the dynamic ideal for live performance. They can stand more rough handling than other mics - you can throw them from hand to hand but don't try bouncing them off the floor! Their weakness is the suspension wires that hold the coil and diaphragm in position and these can snap if the mic is handled too roughly.

They are good at capturing loud, up-front sounds - another plus for live performance - but not so good at capturing quiet sounds and high frequencies over 15kHz. One good thing about dynamic mics is that they're relatively inexpensive. Classic vocalist mics include the Shure SM57 and SM58.

Condenser mics

Condenser or capacitor microphones generally have a much lighter diaphragm and work on a capacitor principle (which is why they are also known as capacitor mics). In a capacitor, an electrical charge is stored between two plates. If the distance between the plates is changed, then the charge changes too.

The diaphragm is positioned in front of a solid back-plate and either may be electrically charged. When sound waves hit the diaphragm, it moves relative to the back-plate changing the capacitance and generating an electrical signal.

Because the diaphragm is thin, it responds better to high frequencies, up to 20kHz, and quiet sounds and it produces a more natural recording. While this would seem to be desirable, some vocals such as rock and punchy stuff can benefit from the inadequacies of a dynamic mic. However, you will often find condensers in studios, even for recording vocals, because they are more versatile and responsive.

Tech terms Phantom power The supply of power from the ground cable of an XLR connector. The voltage can vary but it's typically 48 volts. The power can come from connection to a mixer or a dedicated phantom power box. Pre-amp An amplifier built into some mics that boosts the signal level, often necessary due to the low signal level generated by mics. Proximity effect Some mics enhance the low frequencies of a sound source that is close to the diaphragm. This is the proximity effect. Knowledgeable vocalists and speakers can make use of this to good effect but it can cause problems with inexperienced mic users.

Condenser mics need a power supply to power the pre-amp. This can be a battery inserted into the mic but more commonly phantom power is used where available, generally from a mixer.

The downside to condensers is that they are less robust and more expensive than dynamic mics although recent improvements in microphone technology have improved robustness and reduced prices, too. Popular condensers include the Neumann U47 and the AKG 414.

Back-electret mics

The back-electret is a condenser microphone but the back-plate features an electret material (hence the name) which is permanently charged. This electric charge will eventually wear off, although manufacturers typically claim a life expectancy of 20-25 years. Like condensers, back-electrets also need power.

These mics offer better performance than a dynamic but they are more robust than a condenser so you get close to a condenser performance with greater robustness. Their other major attraction is that they are cheaper than condensers.

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