Completely bamboozled by the microphone spec? Yes. Oh. Right. Well, Martin Sheehan takes time to explain the different types, how they work, which ones you should buy, and what instruments they're best at recording. Pretty conclusive, eh?

A microphone converts sound vibrations into electrical ones so that they can be either amplified or stored. The best microphone might be said to be one whose electrical signals most closely reflect the original sound vibrations. This may not always be the case though — as we shall see...

There are two main features of any microphone by which it may be classed. Firstly, its principle of operation and secondly, its polar response.

The words you'll hear concerning microphone operation are: Dynamic, Condenser, Electret, Boundary effect and Transducer. A dynamic microphone works on the moving coil principle. It's like a loudspeaker only backwards. A diaphragm is attached to the top of a small coil of wire which is suspended within a magnetic field. As soundwaves hit the diaphragm they cause the coil to move within the magnetic field and this in turn causes current to flow in the coil. This current is the useful bit which is tapped off and used to make hit singles.

A condenser (or capacitor) microphone works in a similar way except that the soundwaves are used to distort the opposing plates of a capacitor. The changing shape of the capacitor produces a changing voltage, but the electrical signals produced by this method are very small and need to be amplified within the microphone itself. This calls for a power supply which is usually pumped along the microphone cable from the mixing desk — a system known as "phantom powering". The moving parts of condenser microphones are small and light and this allows them to be more sensitive to high frequencies which have less power than beefy low ones.

In a condenser microphone the capacitor requires a charge to be applied in order for it to work, and this charge is supplied by the phantom powering. Electret microphones, which are otherwise similar to condensers, have their own charge permanently sealed in. A power supply is still required internally in order to boost those tiny signals, but this can be provided adequately by small batteries. Electret microphones do not, therefore, require phantom powering.

Boundary effect (or pressure zone) microphones are becoming very trendy at the moment. Their design incorporates a plate which can be fixed to any boundary off which sound would normally reflect (ie walls, floors, lid of a grand piano). The business part of this type of microphone is mounted so close to the boundary plate that there is no room for indirect sounds to bounce around and confuse things. This results in a very transparent and open sound. Microphones mounted on stands in the conventional manner are more prone to the phase cancellation effects that can be caused by sounds arriving at the microphone after their encounters with various obstacles.

Transducers differ from the aforementioned types of microphone in that they pick up physical vibrations (from the surface on which they are mounted such as the body of a violin or acoustic guitar) rather than airborne vibrations.

In order to choose which type of microphone is best suited for which type of job we also need to consider a thing called its polar response. In order to discover the polar response of a microphone, it is necessary to unplug the lead from its body, lay the microphone on a flat surface and give it a spin. If it comes to rest pointing away from the midday sun then... sorry! — I'll start this bit again.

In order to discover the polar response of a microphone you can have a look at the piece of paper in the bottom of the box it came in. There you will find a circle labelled in degrees. Imagine laying down the microphone with its business end in the centre of this circle and pointing at the nought. Now, a perfect 360 degree circle drawn around this would indicate equal sound pick-up from all directions. If you had it on a mike stand pointing towards you, it would be picking up your voice, the audience out front, and the band to either side. A microphone with a polar response shown like this is known as omnidirectional.

If, however, the line is pulled into the centre at the 180 degree point to form a heart shape, this is known as a cardioid (surprise, surprise) pickup pattern. A cardioid microphone is most sensitive at the front and least sensitive at the rear (not so much of the audience). A hypercardioid pattern will be pulled in towards the centre at the 135 degree and 315 degree points forming the cardioid shape with a bubble on its bottom. Although this pattern would appear to offer less rejection of sounds coming from the rear it does offer a more directional pick up than the cardioid due to its greater insensitivity to sounds coming from the sides (not so much of the band).

A microphone with a polar pattern pulled in at the 90 degree and 270 degree points is said to exhibit (wait for it... ) a figure of eight response. This results in greatest sensitivity at the front and back coupled with greatest rejection at the sides. It is worth mentioning that these polar patterns can vary at different frequencies, especially around the higher ones. Obviously the idea is to get the polar response at all frequencies to coincide over the widest possible range.

This brings us into the point that not all microphones (well, none absolutely) pick up all frequencies with equal sensitivity. It is an expensive business to get a microphone to respond evenly throughout the audio range (approx 20 Hz to 20 kHz). So what happens is that some microphones are produced which are known to have humps and bumps in their frequency response. All the manufacturer does is to look at where those humps and bumps occur, see if they are likely to benefit any particular type of sound, and then market the microphone as being ideal for that role. Good innit!

Choose the right microphone for the right job is a controversial subject but the following method will help to narrow the field. First of all get out all the microphones you have and line them up in front of you. Next, discard the one with the crushed bobbley bit on the end and, finally, prepare to use the other one.

If, however, you find yourself left with more than one microphone to choose from, or indeed you are looking to buy a new one, then hopefully the following discussion about the characteristics of some of the different types available should help to narrow the field when deciding what is best for a particular purpose.

Dynamic microphones are generally cheaper than condensers. This does not mean, however, that condensers are always better. For instance, dynamic microphones can normally withstand higher sound pressure levels. So for close miking of drums (especially bass drums), cabinets and vocals, a good dynamic is less likely to distort.

A good dynamic microphone with a wide, flat frequency response is likely to be the most useful all rounder although you could be paying over £150 for one. There are, however, many applications for cheaper dynamics. The reduction in performance is likely to reveal itself as a lack of response at the highest and lowest frequencies. For this reason the less expensive dynamics are a perfect compromise for miking up toms and guitar cabs where there's not a lot going on at the top or bottom anyway.

The humps and bumps that can be found in the frequency response of some dynamics can be put to good use. The ones which show a lift at around 3-8 kHz are likely to be ideal for vocals. This sort of bump is known as a "presence peak" and is good for improving intelligibility and to help the vocals cut through, especially with a PA. Another feature, usually of microphones with a cardioid response, is that of the "proximity effect". This is characterised by a marked emphasis in bass response when the microphone is used close to the sound source. Again this is useful for PA work as it allows a little of the bottom to be rolled off at the mixer to minimise stage rumbles without losing the bottom end of the sound of whatever is being miked up. A singer with smart microphone technique can also warm up the vocals nicely.

Where a flat frequency response is required, as for recording purposes, a condenser microphone is most likely to be able to provide it. Condensers also handle high frequencies with greater ease. For this reason they are a good choice for overheads on a drum kit. If an omnidirectional pair are chosen, apart from providing a nice sharp cymbal sound, they can also be used to add some room ambience. The proportion of ambience to cymbal will depend on the distance of the microphones from the kit. Omnidirectional microphones are very helpful in picking up sound generated over a wide area as is the case with a piano, for instance. Cardioids are the usual choice for today's multitracking techniques where separation is regarded as very important. Hypercardioids can offer an even greater degree of separation such as may be required between hi-hat and snare.

The rejection characteristics of cardioids and hypercardioids can be put to good use where monitor speakers are employed. A single monitor speaker facing a vocalist will be rejected best by a cardioid, whereas a pair of monitors placed either side in front of a vocalist will be best ignored by a hypercardioid. The ideal combination of pick up and rejection for a pair of backing singers is provided by a figure of eight response microphone placed between the signers as they face each other.

Maximum separation of sound sources can be offered by transducers. These are simply taped to the vibrating surface of the instrument in question. They can be used to mike-up whole drum kits, including the cymbals, although the positioning of the transducers themselves can be a highly critical affair. Another advantage offered by transducers is that if the instrument moves, so do they — this is preferable to losing the sound altogether as an instrument moves off-axis from a microphone.

The advantages offered by electret microphones are that they can offer the wide, flat response of a condenser at a lower price and without the need for phantom powering. This all sounds mighty fine, and for some applications they will be hunky-dory. They do, however, seem a little more susceptible to distortion at high sound pressure levels than either condensers or dynamics. It is also wise to carry a supply of replacement batteries for them. One final word of warning is to treat electrets gently as it is possible to scare off their "permanent" sealed in charge, without which they won't microfy any more.

The open, transparent sound of boundary effect microphones is very rewarding when used to record all manner of acoustic instruments. Their pick-up pattern is generally hemispherically omnidirectional (ie hearing everything away from the boundary wall). Consequently, it is impractical to use them if acoustic separation between instruments is required, although this should prove no problem when recording on a multitrack. Using a pair of boundary effect microphones to record directly to stereo can give very pleasing results, but I'd restrict this technique more towards the string quartet end of the musical spectrum. The main reason for this is that one of the benefits/drawbacks of this type of microphone is that it picks up a lot of ambient sound and I, for one, would rather listen to the oak panelled reverb of chamber music than the inebriated barrackings of a rock gig... on second thoughts!

A final word regarding microphone choice. If the microphones you need are primarily for PA use, then the sheer quantity you may need will make it an expensive operation. Consequently, aim for robustness as you will want to avoid having to replace them. This will mean using dynamic microphones wherever you can. Also, secondhand PA microphones can prove to be a good buy as they come with their own recommendation — the fact that they are still working! For recording purposes it is worth splashing out as much as you can afford on a microphone. After all, this is the point at which the music enters the system, and any degradation of quality that occurs here is permanent. Also, if multitrack recording is your forte you may only need one microphone — so endeavour to make it a good one!