Microphone Center

A microphone senses sound information and transforms it into an electrical format. If you remember that microphones convert sound waves into an electric current, you’ll have a basic understanding of what it does.

But there are many types of mics. So how do I select the right mic for what I need, and keep within my budget? This article discusses the basics any microphone user should know.

We have microphones everywhere today…

• in your telephone or mobile phone handset
• on stage at a rock concert
• on the table in TV chat shows
• clipped to the news reader’s shirt
• hidden in the spy’s hat(!)
• in your sister’s baby alarm
• and of course in any recording studio

Without microphones we could not amplify the speeches in an auditorium, or mellow the sound of Aunt Annie’s attempts at karaoke; we couldn’t hear film or TV sound tracks, or radio broadcasts…

So how did these every-day items come about?

• 1876 - Alexander Graham Bell transmits intelligible words (”Mr Watson, come here, I want to see you”) across a wire from one room to another using a liquid transmitter, and electro-magnetic receiver. (Basic technology of the dynamic mic.)
• 1876 - first commercially practical carbon microphone invented by Thomas Edison to improve Bell’s telephone. Developed it into the basis for the traditional phone model that we know today. Emile Berliner also built a transmitter for voice based on “loose contact” between 2 metal electrodes.
• 1878 - an improved carbon microphone was developed by David Edward Hughes
• 1942 - following the invention of the radio, the broadcast ribbon microphone was created.
• 1964 - saw the birth of the electro-acoustic transducer, used to create the Electret that revolutionized the microphone due to its reliability, affordability and smaller size.
• Throughout the 1970s these dynamic and [tag]condenser microphones[/tag] were developed to provide much higher sensitivity and a clearer recording sound.

Microphone technology is continually advancing but through this brief history you’ll have a better idea of how we got to where we are today.

How it Works

As I said before, a microphone is a device that senses sound information, which enters in the form of air pressure patterns, and converts them into an electric current, called an audio signal.

All microphones have some kind of diaphragm - the microphone’s equivalent of our ear-drum. When a sound arrives at the diaphragm, it vibrates in sympathy with the sound. It is this minute mechanical vibration that is converted into an electrical current, and sends on the audio signal to a mixer or amplifier.

So if you are a recording engineer, you are mostly interested in the accuracy of the transformation that occurs when the sound vibrates the diaphragm.

The exact process of converting micro mechanical movements into audio signals depends on the various microphone technologies used. Here are the main ones you’re likely to come across:

• dynamic - in a dynamic microphone, a moving magnetic field produces varying electric current in a coil of wire
• ribbon - in a ribbon microphone, a moving (metal ribbon) conductor in a magnetic field induces varying current in the conductor
• condenser or capacitor - in a condenser microphone, varying the distance between 2 electrically charged plates results in varying capacitance, with corresponding electrical current variation. “Also referred to as electro-static”
• piezzo-electric - in a piezzo-electric transducer, varying compression creates corresponding electrical potential variation in some materials. (More often used in direct contact with musical instruments eg as under the saddle acoustic guitar pickups)

There are two main types of home recording mics, the onboard microphone and the external microphone. Since the onboard is already built into your computer, there are no additional costs associated. However, they generally are poor quality, more susceptible to feedback and they do not have the ability to pick up the finer details of your sound source.

For these reasons I usually prefer to use a external microphone, although the convenience and quality of some high-end laptop mics make this less of an issue than it used to be. For example, my MacBook Pro records one-one interviews well enough for general use, since it has an excellent onboard microphone.

Filed under: Microphone Basics on June 21st, 2007