AF’s Weblog

October 28, 2009

Microphones: How to choose

Microphone Types

Figure 2

Long the role of the professional sound engineer, choosing the appropriate microphone has now become, with the proliferation of the home studio, the task of the amateur and even the beginner. This choice should depend upon what you’re going to be using the mic for, but also on personal preferences. In this article we’ll be dealing with the two main categories of microphones: dynamic microphones and condenser microphones.
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Signal 1.Sound Waves, 2.Diaphragm, 3.Coils, 4.Magnet, 5.Audio Signal

Dynamic Microphones

These mics generally have a more robust design due to the fact that they are more often used in live settings. They are also usually less expensive and resistant to moisture.

Dynamic microphones use a diaphragm which is attached to a coil of wire placed within the magnetic field of a permanent magnet. When there’s a variation in pressure on the diaphragm it will cause the coil to generate a varying electric current which then needs amplification. Because it’s necessary to attach the coil directly to the diaphragm, dynamic mics tend to have thicker diaphragms than condenser mics. Because of this, recordings are less precise as they’re less sensitive to high frequencies than condenser mics. Popular models include Shure SM57 and SM58.

Dynamic mics generally don’t need any electrical power to operate (as opposed to condenser mics). They are ideal for all-round high sound pressure levels (SPL).

Signal reverse1.Sound Waves, 2.Diaphragm, 3.Metal Plate, 4.Battery, 5.Audio Signal

Condenser or Capacitor Microphones

Also known as capacitor or electrostatic microphones, this type of mic picks up sound through a thin, flexible diaphragm that’s placed next to a metal plate ( as opposed to the rigid diaphragm/coil system used by dynamic mics).

Condenser mics can range from inexpensive Karaoke mics to ultra high level recording mics. Generally, they produce high-quality audio signals and are sensitive to distant sounds and high frequencies. Because of these reasons they are often used in studio recording situations.

Because condenser mics are more sophisticated and are more difficult to manufacture, high quality condenser mics are rather expensive. Condenser mics are ideal for recording voice, acoustic guitars, pianos, orchestral instruments, percussion, and sound effects. Some of the most famous models are the Neumann U47 or the AKG 414.

Phantom Power

Condenser mics require a power source, provided either from microphone inputs as phantom power or from a small battery. The most common type of phantom power is +48v DC. This phantom power is used to charge the diaphragm and plate. It also supplies a small amplifier which boosts the small current* generated by diaphram movements. Phantom power supplies are often built into mixing desks, microphone preamplifiers and similar equipment.

Ribbon Microphones

Ribbon mics are a type of dynamic microphone. They use a very thin metal ribbon that’s suspended between the poles of a powerful magnet. Sound waves cause this ribbon to move and create an induced current. Voltage output of older ribbon mics is much lower than dynamic mics so a transformer is used to increase voltage output and to increase output impedance. Modern ribbon mics avoid this problem by using improved magnets and more efficient transformers. Ribbon mics are usually bi-directional (see next page on pick-up patterns). Classic models include the RCA 44 and 77 as well as Royer mics.

Now let’s take an even closer look…


Other Considerations

Fig.1: A Typical Frequency Response Chart Signall

Frequency response

This is a measure of the microphone’s sensitivity to different frequencies. It’s a characteristic of all mics that some frequencies are exaggerated and others attenuated. So the frequency response shows how a particular mic responds to particular frequencies.

A chart usually shows a mics’s frequency response. The x axis shows frequency in Hertz, the y axis shows response in decibels. A higher value means exaggeration and a lower value means attenuation. A completely flat chart (frequency response) would show that the mic is equally sensitive to all frequencies. But in reality a totally flat response is impossible and even the best mics have some degree of deviation. Also it should be noted that sometimes a mic is especially chosen for the specific frequency response that it has. For example, a mic with a frequency response adapted to the human voice would be a good choice for recording in an environment with low frequency background noise.

Self Noise

This measurement represents the lowest point of a mic’s dynamic range. This is important if you want to record very soft sounds. Basically, the lower the number is, the better.

Maximum SPL (Sound Pressure Level)

This is the maximum level a mic can accept. Here, the higher the number, the better. But one should note that mics with very high SPLs have higher self noise.

Sensitivity

Indicates how well the mic converts sound pressure into output voltage. The higher the number, the higher the sensitivity. A highly sensitive mics produces more output and will therefore need less amplification after. It should be noted, however, that a higher sensitivity rating does not necessarily make one mic better than another.

To read the full detailed article see:  Microphones: How to Choose

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