The Mic Demystified: Part 1

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Confused by all the different kids of microphones available to you? If so, this little intro to mics might be just what you need to clear up some of the confusion.

Ok, our topic is Microphones. I'll discuss some common types of mics and how they work. First off, a microphone is a transducer, which is a device that transforms energy into another corresponding form of energy. Other transducers you may be familiar with are speakers, headphones, and yes… your ears. In this case, the 'energy' being converted by the mic is sound pressure level, or SPL, which is received by the diaphragm of a mic then transformed into a corresponding small AC voltage (mic level).

The most common microphones used in recording today fall in these categories:

  • Dynamic - Use Electromagnetic Induction, phantom power not needed and may damage mic
    • Moving-Coil - uses diaphragm connected to a wound coil that moves within a magnetic field to induce voltage. Can handle high SPL.
    • Ribbon - uses a corrugated metal 'ribbon' looking similar to a filament inside a light bulb or fuse. Very fragile and sensitive to SPL.
  • Condenser - Utilizes Electrostatic Induction, phantom or other power source often required. An internal Impedance Conversion Amplifier (ICA) is found in these mics. Usually these can handle high SPL or they have a PAD (pre attenuation device).
    • Tube - has its own power supply (new models may use only phantom power) and uses it to charge (polarize) its diaphragm and back plate. It draws its output signal from the difference in capacitance between the diaphragm and back plate as the diaphragm responds to SPL. Also uses a vacuum tube in its amplification
    • Electret - The most affordable type, utilizing solid state electronics, uses 2 permanently charged plates for the diaphragm and back plate but still requires power (phantom or battery) for the ICA.

Now that you've learned about the different types, you must learn the different polar response patterns of a mic's capsule. The response pattern tells you how or from what direction a mic will pick up sound.

These are the different types:

Omnidirectional (pressure)

This pattern receives SPL from all around it. In Fig. 1 you see the response pattern of an omni mic. Its capsule is located at the origin of the x and y axis pointed towards the 0 degree mark. As you can see the circle represents that it will receive SPL equally from all angles.

Directional (pressure-gradient)

These patterns are more directional, meaning that they have specific points of SPL rejection.

Unidirectional - Picks up sound primarily from one direction.

  • Cardiod - Sound is rejected from the back.
  • Super-Cardiod - Like the Cardiod pattern but more sound is picked up from the back and front lobe is more directional.
  • Hyper-Cardiod - Like the Super-Cardiod pattern but even more sound is picked up from the back and front lobe is even more directional.

Bidirectional (commonly known as figure 8)

As seen in fig.3, it will receive SPL from in front and back of the capsule but reject sounds coming from the sides. This characteristic is very valuable for stereo imaging as we'll discuss in Part 2 of this article.

Most Dynamic mics have a fixed polar pattern. Condenser microphones can have the ability to switch patterns and those that do will have 2 capsules to help achieve the different responses by manipulating the 2 signals.

*Stay tuned for The Mic Demystified: Part 2 for some common applications of these different mic types, to see how these polar response patterns can be used in recording, and some tips on stereo imaging.

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