All About Microphones
Microphones can play an important role in the use of
audio, by allowing you to record your own sound clips. Different microphones
have different characteristics and some of the most important are described
below.
There are many different types of microphones to
choose from. The following information from How Stuff Works - Question of the
Day: Microphones (http://www.howstuffworks.com/question309.htm),
describes the major categories of microphones.
- Carbon microphones
- The oldest and simplest microphone uses carbon dust. This is the
technology used in the first
telephones and is
still used in some telephones today. The carbon dust has a thin metal or
plastic diaphragm on one side. As sound waves hit the diaphragm they
compress the carbon dust, which changes its resistance. By running a current
through the carbon, the changing resistance changes the amount of current
that flows. See How
Telephones Work for more information.
- Dynamic microphones - A dynamic microphone
takes advantage of
electromagnet effects. When a magnet moves past a wire (or coil of
wire), the magnet induces current to flow in the wire. In a dynamic
microphone the diaphragm moves either a magnet or a coil when sound waves
hit the diaphragm, and the movement creates a small current.
- Ribbon microphones - In a ribbon microphone
a thin ribbon is suspended in a magnetic field. Sound waves move the ribbon
which changes the current flowing through it.
- Condenser microphones - A condenser
microphone is essentially a capacitor, with one plate of the capacitor
moving in response to sound waves. The movement changes the capacitance of
the capacitor, and these changes are amplified to create a measurable
signal. Condenser microphones usually need a small battery to provide a
voltage across the capacitor.
- Crystal microphones - Certain crystals
change their electrical properties as they change shape (see
How Quartz Watches
Work for one example of this phenomenon). By attaching a diaphragm to a
crystal, the crystal will create a signal when sound waves hit the
diaphragm.
| Sound
Pick-Up Patterns
or Directionality |
How a microphone picks up sound is another important
quality. The following information comes from Microphone Pickup Patterns and
Typical Gain Before Feedback (http://www.applegateandcompany.hispeed.com/Sound/
microphone_pickup_patterns_and_t.htm)
- Omni-Directional - The simplest microphone
design will pick up all sound, regardless of its point of origin, and is
thus known as an omni-directional microphone. They are very easy to use and
generally have good to outstanding frequency response.
- Bi-Directional - It is not very difficult to
produce a pickup pattern that accepts sound striking the front or rear of
the diaphragm, but does not respond to sound from the sides. This is the way
any diaphragm will behave if sound can strike the front and back equally.
The rejection of undesired sound is the best achievable with any design, but
the fact that the microphone accepts sound from both ends makes it difficult
to use in many situations. Most often it is placed above an instrument.
Frequency response is just as good as an omni, at least for sounds that are
not too close to the microphone.
- Cardioid - Named for the heart-shaped
pick-up pattern, this pattern is popular for sound reinforcement or
recording concerts where audience noise is a possible problem. The concept
is great, a microphone that picks up sounds it is pointed at. The reality is
different. The first problem is that sounds from the back are not completely
rejected, but merely reduced about 10-30 dB. This can surprise careless
users. The second problem, and a severe one, is that the actual shape of the
pickup pattern varies with frequency. Variations of the cardioid microphone
include a super-cardioid microphone, which has a tighter pickup
pattern than a regular cardioid microphone--it doesn't "hear" as much sound
from the sides; and a hyper-cardioid microphone, a very specialized
microphone. A good example is a shot-gun microphone. The microphone "hears"
only what it is pointing at--nothing from the sides and very little from the
back.
There are many different styles of microphones and they
come in many shapes and sizes.
- Handheld microphones are (as the name
suggests) held in a person's hand or may placed in a microphone stand.
- Lavalier microphones are usually clipped on
a speaker's clothing, such as their tie or lapel. These microphones may be
wired or, more popularly, wireless. Hanging microphones are usually
suspended by their own cables and may sometimes be found in orchestras or
choirs.
- Shotgun microphones are often mounted on
poles and pointed toward the speaker(s). These microphones may often be
found when movies and television shows are being made.
- Computer microphones are becoming more
popular as many computers and digital devices now include built-in
microphones.
The Basics of Computer Microphones
Multimedia microphones are fairly simple pieces of equipment, designed
mainly for game play, recording audio clips for use with computerized
presentations or for use with teleconferencing software. Most multimedia
microphones utilize arms or necks that are 7 to 9 inches in length, and most
rest in a stand on the desktop. However, the line between a multimedia
microphone and a traditional microphone is becoming more blurred.
Traditional handheld microphones often can be converted to work with a
computer as a multimedia microphone using a simple jack or plug. Some
multimedia microphones can be worn as a mouthpiece with a headset as well,
making them especially handy for voice-recognition applications.
How to Shop for a Computer Microphone
Flexibility is one of the best features you'll find in a multimedia
microphone, and it's worth paying a little extra for. A microphone with a
flexible neck is going to be far more comfortable to use, no matter where
you're trying to use it. If the microphone is part of a headset, the
microphone should be adjustable with a flexible neck, allowing you to place
it directly in front of your mouth. A microphone sold as part of a headset
also should also easily disconnect from the cord so you can move around
without constantly having to remove the headset. For those who need to
create professional-style audio clips on their computers, investing some
extra money in a traditional handheld microphone and converting it for use
with multimedia applications will be worth the added cost. While multimedia
microphones are solid performers, they can't compete in quality of audio
with traditional microphones.
Where to Buy a Computer Microphone
Because multimedia microphones are so inexpensive--usually ranging
anywhere from $5 to $20--you won't have to search too hard to find some good
deals. Any store that carries a collection of computers and PC peripherals
should have plenty of brands of multimedia microphones from which to select.
Probably the best combination of price and selection will come from a
computer superstore such as CompUSA or an electronics store, such as Best
Buy or Circuit City. Radio Shack is also a good source for inexpensive
microphones. Because multimedia microphones are so inexpensive these days,
repairing them usually is a waste of effort and money, so the store's
service center isn't overly important. If you plan to record a large number
of audio clips for integration into PowerPoint presentations or web pages,
you may want to look into buying a professional-style microphone. In this
case, you will spend more and you may want to search the web for microphone
manufacturers, or you can visit a music equipment store. Before purchasing,
though, make sure the microphone you choose can be used with a computer. You
may need to buy additional jacks or plugs at a computer equipment store or
from the microphone's manufacturer to make certain it connects properly to
you computer.
Many inexpensive microphones for use with computers are
available in the $5 - $50 range. One model manufactured by Koss (see image
below), is a uni-directional microphone that comes with a table top stand and is
flexible so that it can be bent to accommodate speakers of different heights.
You can usually find this type of microphone for about $10.
IMPORTANT NOTE:
The sound quality of your recorded audio is fair
when using this type of microphone, however, the quality of your computer's
sound card will usually determine the quality of the recording at least as much,
if not more than the type of microphone you are using.
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The cable above has a
metal tip called a mini-plug on one end. The other end is wired directly
into the base of the microphone. The plug end is called the male end,
and is one eighth inch in diameter, so sometimes you may hear this type
of connector called a 1/8th inch connector. This type of cable is often
used for audio and is frequently found on headphones used with portable
audio players. A single stripe seen near the end of the metal plug
indicates that this is a monaural cable. Stereo connectors usually have
two stripes. |
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Another popular computer microphone does not plug into the computer's
sound card, but instead uses a USB connection. The picture at left is a
Logitech USB Desktop Microphone that sells for about $30. This
microphone should provide good quality regardless of the type of sound
card your computer has since it bypasses the sound card. It does not
require any additional software or drivers and should work well on any
computer that has a USB connection. |
When you first plug a USB microphone into a PC, you may
need to change some audio settings to make sure the computer recognizes the
microphone. In the Windows XP operating system, you should first go to the Start
menu and click on Control Panel.
Next click on the Sounds and Audio Devices icon (as
shown below left), or if you are in the Category view (as shown below right),
click on the Sounds, Speech and Audio Devices link.
This will bring up the Sounds and Audio Devices
Properties box. Click on the Audio tab.
Use the pull-down menu under the Sound Recording in the
middle of the box and the name of your USB microphone should appear in the list.
Make sure it is selected and then click Apply and OK.
