What Are the Different Types of Wired Microphones?

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What Are the Different Types of Wired Microphones?

With well over a hundred years of history and development, wired microphones have evolved from simple experimental designs to sophisticated and reliable devices capable of impressive quality. All microphones are a form of transducer, which means they function by converting one form of energy to another. In the case of microphones, they covert the energy of sound waves (from a singer, for example) to electrical current, which can then be transferred via the microphone's cable to other devices, where it can then be acted upon in many ways. It can be recorded, amplified, and reproduced through a loudspeaker, or transmitted hundreds or even thousands of miles down a telephone line and over a global network. The microphone is always the first in line in this complex chain of technical events. If the microphone fails, the chain is broken even before it starts. Fortunately, that long evolution and experience has produced real advances and modern wired microphone technology is stable and reliable.

The Basic Principle of Microphones

The basic principle is similar in all conventional wired microphones. Sound waves strike the microphone and cause a sensitive element to vibrate with exactly the same vibration patterns. The movement of this element, in turn, causes a varying electrical current to be generated (or an already-present electrical current to be modified), in a way that exactly replicates the physical movement of the element and original sound wave patterns.

Microphone Characteristics

While the basic principle is the same, various constructions of microphone have varying characteristics. Certain types are better suited to certain applications. Important microphone properties include the following:

Sensitivity

This refers to how well the microphone is able to collect and convert sound waves to electrical signals. Price is normally a good indicator of a microphone's sensitivity. Microphones with low-sensitivity have no particular advantage except that they're cheaper to produce and to buy.

Frequency Response

Frequency response refers to how sensitive a microphone is to sound waves at different frequencies. Most microphones are better at picking up sounds within a certain frequency range than others. Microphones that are designed for speech, for example, tend to have a fairly limited frequency response as speech itself lies within a fairly narrow frequency band. A symphony orchestra, on the other hand, has a wide frequency range ranging from the lowest double bass notes up to the highest and shrillest sounds of flutes, piccolos, and violins. Virtually the whole audible spectrum is there. Wired microphones that are set up to record their performance must be capable of capturing the entire range of high and low notes either individually or in combination with different microphones being used to capture different frequency ranges. Their outputs can then be fed to a mixer to achieve the best overall balance of sound.

Directionality

Relative to how they're positioned, some microphone types respond to sounds better in certain directions than in others. Some microphones can pick up sounds equally well in any direction. Other microphones, by contrast, are designed to pick up sounds from the direction in which they're pointed and to be less responsive to sounds approaching from the sides. Most manufacturers publish a graph of their microphones' typical pick-up pattern as part of the specification sheet supplied with the microphone. The table below shows the main types of directionality employed in microphone design.

Omnidirectional microphones

Omnidirectional microphones pick up sounds equally well in all directions. Most general-purpose microphones are omnidirectional. They are also especially suited to sound detection roles in some security systems.

Unidirectional microphones

Unidirectional microphones are more sensitive to sounds originating directly ahead and less sensitive to sounds coming from other directions. This provides a great advantage when it's desired to pick up a single sound source and block, or at least significantly reduce unwanted sounds from elsewhere. They have a very important use in the live and studio music recording industry. So-called shotgun microphones are unidirectional microphones that have a very narrow directional sensitivity. As their nickname suggests, they can be very precisely aimed at their target and will ignore everything else. They have specialist applications in areas such as TV sports coverage.

Bidirectional microphones

Bidirectional microphones are capable of responding to sounds directly in front and also directly behind while blocking out sounds from the sides. This type of microphone finds a lot of use in face-to-face live interview situations but has often been thought of as problematic for stereo recordings.

Stereo microphones

These consist of two independent unidirectional microphones combined in a single unit. Each is optimised to capture sounds from left and right positioned sources, respectively. The final output is a stereo audio signal.

Types of Wired Microphone

Different methods of converting the element's physical vibrations to electrical current patterns are used in wired microphones and this has resulted in different families of microphones, with varying characteristics that suit particular situations.

Dynamic microphones

The sound-sensitive element in a dynamic microphone is a moving coil connected to a surface diaphragm and suspended within a magnetic field. Sound waves strike the diaphragm, which transfers them as physical vibrations to the coil. As the coil then vibrates within its magnetic field, it generates a small electrical current that varies in exact accordance with its vibrations. Dynamic microphones are popular in live situations as they tend to be less susceptible to unwanted audio feedback than other microphone types.

Ribbon microphones

Ribbon microphones are similar to dynamic microphones as they rely on a magnetic field to generate the signal. Using a metallic ribbon as the element, however, produces a marked figure of eight pick-up area, which makes ribbon microphones effective bidirectional microphones.

Condenser microphones

The method employed in condenser microphones is an arrangement in which the sound vibrations vary the element’s capacitance, which, in turn, varies the output signal current. Condenser microphones typically have very good frequency response and directionality and are often used in live music recording as well as studio recording.

Crystal microphones

Crystal microphones make use of a natural property of certain crystals and other materials known as the piezo-electric effect. Physical vibrations cause the crystal to generate small electric currents that mirror the wave pattern of the vibrations. Crystal microphones are often used as contact microphones. A common example is their use on acoustic guitars, where a contact microphone may be affixed to the body of the guitar. It responds to the guitar's vibrations directly through the wood rather than through air.

Fibre optic microphones

Fibre-optic microphones are a relatively new introduction to microphone technology. The microphone's diaphragm, when vibrating in response to incoming sound waves, disturbs a laser beam delivered via optical fibres. These disturbances can be recorded and reproduced as electrical signals. Although based on a fairly new technology, fibre optic microphones already show very impressive audio sensitivity and frequency response characteristics.

Microphone Cable

An essential component of wired microphones is the cable that transfers the output signal to any suitable equipment for further processing. The cable used in a good-quality microphone will have equally high-quality conductors and effective shielding to eliminate radio interference from various sources. Microphone cables need to be in good condition and replaced when necessary. Cables that are damaged can easily cause interference and distortion.

How to Find Wired Microphones on eBay

Microphones are a highly-popular item for sale on eBay. Thousands are available at any given time. Simply searching for "wired microphones" using their search function returns a sizeable but unsorted list.
Fortunately, eBay's category system is available to filter out any microphone types that aren't required. The eBay category Pro Audio Systems is a rich source of wired microphones. To find this, click on All Categories on the home page, then on Musical Instruments before finally Pro Audio Equipment. Within that category, there are subcategories and filtering options that list the microphones in convenient groups, such as: by type, by price, by condition, by manufacturer and more.

Conclusion

One impressive property that microphones of a reasonable quality have is that they keep their quality indefinitely. Provided the microphone is handled with reasonable care, it can be expected to perform well and reliably for many years.

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