Quick Guide To Microphones

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

Dynamic MicrophoneThe 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 classic Shure SM58 microphone is probably used by more singers than any other mic. Its cardioid response and ruggedness make it an idea performance mic.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.
Condenser Microphone

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 bacThe Neumann M 147 is a tube condenser microphone that builds on the popularity of thje company's U47. Its cardioid response and sensitivity make it an ideal studio mic.k-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.

Other microphone types

There are several other mic types that deserve a mention. The tube microphone is a condenser with valves that offers ‘valve warmth’ but that must be weighed against the cost, fragility and increased background noise with low-level signals.

The ribbon microphone is now quite rare although you may find them in high-end studios. They are a form of dynamic mic using a ribbon in front of a metal plate. They are very sensitive and are therefore very good for quiet sounds and excel at close-micing. They are very fragile and have largely been superseded by condensers except for specialist situations.

So-called bass mics are dynamics with large diaphragms. They are very robust and used with sources that generate loud sounds such as inside a bass drum but they have poor high frequency response.

Pickup patterns

The other aspect of a microphone you need to consider is its response or pickup pattern. Some people think that if you point a mic towards something, that’s all it records. Not so. There are three common response patterns plus two variations.

Omni-directional microphone pickup pattern.A mic that can pick up sound from a full 360 degrees around it is known as omni-directional and is ideal for recording background and ambient sounds. They generally lack any proximity effect and so are commonly used for vocals.

Bi-directional microphone pickup pattern.A bi-directional pattern records sounds from in front of and behind the microphone. The response looks like an ‘8’ and such mics are often called ‘figure of 8 mics’. They are often placed above a sound source.

 

Cardioid microphone pickup pattern.A cardioid response has a heart-shaped pattern, picking up most sounds from in front of the mic, a little from the sides and almost none from behind. These seem ideal for minimising noise which might be in front of the instrument or singer but they tend to minimise such noise rather than eliminate it and they can be subject to the proximity effect which causes the tone of a speaker’s or singer’s voice to change as they move closer to or further away from the mic.

Hyper-cardioid microphone pickup pattern.The hyper-cardioid design is a tighter version of the cardioid. It’s more directional, has a flatter response and is less sensitive to sound behind the microphone. You might lose a little warmth but the benefits in a noisy environment may be worth the trade-off. Live, with monitors on stage, it’s a good choice.

Shotgun microphone pickup pattern.Finally, there’s a shotgun or directional response which is a more sensitive bi-directional variant. At extremes, these are the sort of mics you see being used by snoopers and tappers and people listening in to conversations of individuals in a crowd. CIA stuff. They are not used so much in music.

Putting it all together

Ideally you will have separate mics for different purposes such as recording vocals, acoustic guitars, micing drums and so on. In practise you may not have the luxury or the budget so here’s a few guidelines to help, but do bear in mind that this is where personal preferences and the black arts come to the fore.

In a studio, the condenser is the most versatile and one with a cardioid response should serve as a good all-rounder. Vocals can benefit from an omni-directional mic providing there are no sounds in front of the singer. Having said that, some vocalists prefer the response of a dynamic mic because it makes them sound better.

For live use with rock material or vocals that need to be punchy, up-front and in-yer-face, a dynamic mic is the answer. If you need the mic to double in the studio then consider a back-electret while saving for separate condenser and dynamic mics.

Recommending a single mic to record a range of acoustic instruments is difficult as different mics afford different recording techniques. An omni-directional mic can be dangled or placed on a stand in front of an instrument. Condensers would usually be recommended although dynamic mics are commonly used for micing drum kits. The placement of mics for recording instruments, however, is beyond the scope of this short feature.

If you can only afford one mic and want a good all-rounder, a back-electret is a good choice.

If you get the opportunity to try different mics, you may be surprised at the difference they make to the recording and there’s nothing wrong in preferring a dynamic to a condenser for vocals or a cardioid to an omni if you prefer the sound and can work the proximity effect. That’s where art overtakes science in the world of music.

For more info…

Many microphone manufacturers’ web sites include a lot of useful information about microphones. The Sure site is a mine of essential information:
Buyer’s Guide
How Tos, Tips & Tricks