How to choose the right mic for the job
Before buying a microphone, it is essential to make sure that it will do the job you want it to do. This means that you have to clearly understand which application(s) the microphone was designed for.
There is no such thing as an all-purpose microphone that is ideal for every application. Differences in pickup pattern, maximum SPL constraints and noise floor should all be taken into account during the selection process. All microphones are made for a certain purpose or sometimes a compromise between several related purposes.
Is it primarily for recording in a studio or home studio, is it for live use or perhaps both? Is it meant for one specific instrument or sound source or should it be for more general use? Is it to be mounted on a stand, an instrument, a head or is it handheld?
Is your budget limited? Quality always costs. You can save money on features you don’t need, but to most people quality is a feature they do need.
Live vs. studio miking
The main difference between these two environments is not the sound source itself but the surroundings.
The studio is a relatively controlled environment, where you often are given a second chance if the result is not satisfactory. For that reason your expectations of the result will, of course, also be much higher. That means the desire for clarity, definition and low noise has no upper limit.
In order to compensate for poor sounding acoustics or to get more channel separation when multiple instruments are recorded, directionality can be more important than definition and noise
The main problem with a live setting is the large number of other loud sound sources other than the one you wish to amplify or record such as the P.A. front and the monitors that can cause feedback , or the other musicians and their amps that are often much louder than the voice or softer instrument you need to mic.
This means that the primary objective for a live microphone is separation and secondarily good off-axis sound (sound taken in from the side/back of the microphones).
If the monitor and amplifier level on stage is controlled and relatively low, it is possible to gain more clarity and definition by using less directional microphones.
Dynamic vs. condenser mics
Dynamic microphones are, in brief terms, a reverse dynamic loudspeaker (you can actually use a loudspeaker as a dynamic mic – don’t try the opposite). It’s a moving coil in a permanent magnet. The diaphragm is attached to the coil, and when it moves, it produces varying current through electromagnetic induction.
The construction of dynamic mics is quite simple, which makes them rugged and inexpensive and they don’t require external power. The rugged heavy construction also makes them more ‘forgiving’ with less resolution. Most common applications are live – especially on vocals, drums and amplifiers.
A condenser microphone consists of a capacitor, where one side is the diaphragm and the other is the back plate which is polarized either from an external power source or by prepolarization. As the diaphragm moves it changes the capacitance, and these changes are then amplified to make a transmittable signal.
All condenser mics need external power (referred to as phantom power) to energize the internal electronics. They produce a sound signal of a much higher quality than the dynamic mics, but they are more expensive, and a little more fragile to use, however newer technology has made them far more resistant to rough use, and the use of condensers in live applications is on the rise.
Directional/cardioid vs. omnidirectional microphones
Microphones can have different directional characteristics. Omnidirectionals that pick up the sound all around them, and cardioids that mainly pick up the sound directly in front of them. Other directional patterns are: bidirectional/figure 8, supercardioid, hypercardioid, and wide cardioid.
Generally a cardioid sounds appealing, since in a musical setting you only want the sound source and rarely want to record or amplify the surroundings. But directionality has a price and that sometimes is not worth paying.
Directional microphones need to have a much softer diaphragm than an omni. This softness results in handling, pop and wind noise which puts a limit to how close you can get to a vocalist, even when using pop-filters.
A directional mic also suffers from proximity effect, which means that the closer you get to the sound source the louder the low frequencies get and vice versa.
A cardioid microphone can be adjusted to be linear at the distance it is normally used. A vocal microphone for live use, for example, is adjusted to be linear at a distance of approximately 1 – 2 cm and at longer distances the low frequencies drop dramatically. A studio microphone is typically adjusted to work at a longer distance.
In the example of the DPA 4011-TL, when used closer than 30 cm it gives a low frequency boost, and when used further than 30 cm it gives a low frequency rolloff. That means that from any other distance than 30 cm equalization is needed unless the proximity effect is desired.
Additionally the off-axis sound of a cardioid is less linear than that of an omni. It is very hard to reduce the level of sound taken in from the sides without some coloration, and some directional microphones have a notably poor off-axis response.
This means that sound entering the microphone from the sides and the rear are more or less strongly colored – the industry names this “the curtain effect”. This effect can be seen on the microphones polar pattern as ‘spikes’.
On the other hand, miking live with high level monitors can make the omni mic feed back , which makes the cardioids more suitable for this application, although the use of in-ear monitors reduces that problem.
If you choose an omnidirectional microphone, channel separation may be less precise than with a directional microphone, because the omni will pick up sound from all directions. Therefore, if channel separation is preferred, the ratio between direct and indirect sound can become more unfavorable with an omni.
The omni, however, can be moved closer to the source, without the penalty of proximity effect. As a general rule it can be said that if we place a cardioid at a distance of 17 cm to the source, then an omni placed at 10 cm gives the same ratio of direct and indirect sound as the cardioid.
Multi-pattern microphones with both omnidirectional, bidirectional and cardioid characteristics will always compromise the sound quality. It may be very convenient to have a 3-in-1 solution, but the drawback is reduced performance in each mode.
Due to the need of a pressure gradient design, a multipattern microphone in omni mode has many of the weaknesses of the cardioid, such as popping, handling and wind noise and a less linear off-axis sound. In fact a multi-pattern microphone in the same mode can have different characteristics depending on the frequency.
Large vs. small diaphragms
Before choosing between a large and a small diaphragm microphone it is important to know the difference in features between them, and microphone behavior can not be compared with that of a loudspeaker when considering size.
A large diaphragm microphone is not better at reproducing low-frequencies, but it may be less precise in reproducing high frequencies, which may make it sound as if it has more low end.
A small diaphragm has a higher self noise due to the fact that the small diaphragm is less compliant and therefore more sensitive to the bombardment of air molecules that causes some of the self noise of a microphone. And since the large diaphragm is softer than the small, it is easier to move and therefore more sensitive – even at very low levels.
This means that the small diaphragm, because it’s stiff, can handle a higher sound pressure without clipping or distortion, but is less sensitive and needs more amplification, which also adds a little noise.
When reproducing very high frequencies, large diaphragm microphones have a more limited range than the small diaphragms. This is caused by three factors:
- A large diaphragm tends to break up and will no longer act as a true piston. This phenomenon is also recognized in loudspeaker technology and is the reason why loudspeakers are manufactured with different sizes of diaphragms to handle different frequencies.
- The weight of the diaphragm will attenuate the displacement of the diaphragm for higher frequencies.
- The diffractions around the edges of the microphone capsule will limit the microphone’s capability to handle very high frequencies.