Choice of microphones is a very personal thing and there are many factors to take into account. There is no one general ‘one microphone to fit them all’, but a range of microphone types that all have their own characteristic sound textures.
What Is a Microphone?
Microphone is a device that captures the audio vibrations ie the Acoustic Energy and converts it in to Electrical energy Faithfully.
This is ‘dynamic’ in the same sense as a dynamo,which is device that turns movement into electricity. For example an old-‐style bicycle dynamo rotates a coil of copper wire inside the field of a magnet to create electricity to power the front and rear lamps.
In the same way, a coil of wire connected to the diaphragm of the microphone vibrates inside the field of a magnet in response to incoming sound waves. The current induced in the coil varies in proportion to the sound wave, thus turning an acoustic signal into an electrical signal.
The dynamic microphone produces an electrical signal directly and does not need to be powered. The advantages of the dynamic mic are its simplicity and robustness. The disadvantage is that the diaphragm is weighed down a little by the coil, hence it isn’t quite as responsive to quickly-‐changing transients as other types of mic. You wouldn’t expect a dynamic microphone to capture all of the zing and sizzle of a cymbal. But on drums it can capture a sound that is solid and satisfying to the ear. The dynamic microphone works well on electric guitar speaker cabinets too.
Dynamic microphones are often used for vocals in live sound. This is largely due to historical reasons because condenser microphones used to be bulky and delicate. But even now that there are condenser microphone available that are purpose designed for live vocals, their generally higher cost is a disadvantage when dynamic mics work very well for the purpose.
Small-‐diaphragm condenser microphone
The capacitor microphone works on the principles of electrostatics and needs to be powered, normally with a 48-‐volt system known as phantom power. They need this a) to charge the electrostatic diaphragm and backplate (which forms the capacitor), and b) to power the internal amplifier that is
necessary, the output from the capsule of the mic being very weak. The point in having a small diaphragm, some 12 millimeters or so in diameter, is that a small diaphragm can be extremely responsive to sound. A larger diaphragm will tend to have a less accurate frequency response to sound that doesn’t arrive at the mic directly on-‐axis, and a larger diaphragm may have resonances that color the sound. An even
smaller diaphragm can be used for newsreaders’ clip-‐on mics for example, but they tend to be more noisy.
If you’re looking for an extremely accurate sound therefore, the small-‐diaphragm capacitor microphone is the one to go for. A more accurate sound isn’t necessarily better, and can sound ‘small’ compared to a more hyped-‐up mic. But if you want to capture things exactly as they are in real life, it’s the mic type to choose.
Large-‐diaphragm condenser microphone
Before microphone manufacturers found ways and means of shrinking the condenser microphone, all condenser mics had what we would now think of as a large diaphragm. Although there is no hard-‐and-‐fast dividing line between small-‐diaphragm and large-‐ diaphragm, you can think of 24 mm as being large. Bear in mind that you would have to look at a mic’s specification on this. Some quite bulky mics have surprisingly small diaphragms inside. The advantage of this type of mic is that it gives you the kind of sound you would often want in the studio -‐ not natural exactly, but a rich and warm sound that flatters anything you put in front of it.
Because of the larger diaphragm that captures sound vibration over a wider area, it has the potential to be quieter than a small-‐ diaphragm capacitor microphone, but it would be unusual to find this a real-‐life benefit of significance.
The large diaphragm has the disadvantage that it is likely to be more directional at higher frequencies then lower. When it is used head-‐on then this won’t be an issue. But when the off-‐axis pickup is important, such as when two mics are used as a stereo pair, then it is worth listening out for.
This design goes back to the early days of condenser microphones when the internal amplifier had to have a vacuum tube as its
active element because transistors had not yet been invented or had not become practically usable. Although some vacuum tube microphones from the past had small diaphragms, we now tend to see the vacuum tube and large diaphragm as going hand-‐in-‐ hand .
The advantage of the vacuum tube microphone is that the tube amplifier tends to create a small amount of distortion of a pleasant kind that the ear interprets as ‘warmth’. For vocals, the effect can be magical.
Although it would rarely be worthwhile to seek out a vintage example of any other kind of microphone, vintage vacuum tube microphones are often VERY desirable -‐ and correspondingly expensive!
The ribbon microphone is a special kind of dynamic microphone. But where the conventional dynamic microphone has a coil of wire attached to the diaphragm, the metalized ribbon is both the coil and diaphragm combined. Because the ribbon is so light, it can be as responsive as a capacitor microphone, although the tone tends to be a little darker. Ribbon microphones are often thought to provide a detailed but slightly dark sound. This makes them useful as an extra artistic tool to play with in the studio.
Ribbon microphones are commonly fragile, to the point that some would advise not to walk quickly while holding one or the ribbon could be damaged or dislodged by the passage of air.
The ribbon mic doesn’t need powering (apart from special types with their own internal amplifier). However their output is generally low and it is worth taking note of manufacturers’ recommendations when choosing a preamp.
The electret microphone is a special type of condenser microphone where the diaphragm is pre-‐polarized and doesn’t need to be powered. The internal amplifier still needs power. This can often come from a small battery as an alternative to phantom power, but battery-‐only electret mics are likely to be less sensitive and have a lower maximum sound pressure level (SPL) handling capability.
Early designs of electret microphones were often thought to be inferior due to the limited choice of material for the diaphragm. But the improved back-‐electret design removes this limitation by pre-‐polarizing only the backplate. Indeed some of the most accurate microphones in the world are back-‐electret types so this should no longer be an issue in microphone selection.
Another type of microphone that has fallen out of use, for sound traveling through air, but still has wide-‐ranging applications in audio. This is the piezo or ceramic microphone, which works by the piezo-‐electric effect where bending a special crystal can create an electric voltage.
The piezo design these days is used as a contact mic, either as a multi-‐purpose contact mic for any instrument you can stick it onto, or as an under-‐bridge pickup for acoustic guitar. Either way, it picks up vibrations directly from the sound source, not through the air. This has advantages in isolating the instrument from other sounds, but is usually some way from being entirely natural and is only used when there are distinct advantages in doing so.
Fishman BP 100
Knowing and recognizing the distinctive sound textures of these types of microphones is an important skill for every engineer, producer and musician. The Art Of Micking is slowly getting to be a lost art, reason being that every one tends to use samples and very rarely wants to record an acoustic instrument. I urge each musician to try and record minimum, one acoustic instrument in their track by applying the art of micking in the right studio and with the right Engineer.
Microphone can capture the sound only as good as the source!!!