Have you ever wondered how you hear different sounds coming out of your left and
right speakers and not the same sound on both? This dual sound is called stereo sound. Stereo sound is produced by stereo microphone recordings from a studio or concert setting. To give you a better understanding on this works here's an explanation of a mono-microphone. Microphones work by intaking sound waves which vibrate a diaphragm connected to an amplifier circuit.
The diaphragm is typically made out of a material called electret, which is a type of plastic. The electret has a maintained charge on it which allows electricity to flow. The disadvantage to using this plastic material is that it only holds a charge for a couple years before it has to be replaced.
As the diaphragm moves the sound waves are converted into an electrical signal through the amplifier, called rarefactions and compressions. The signals from the amplifier are then recorded onto a medium like a tape, cd, or record. So, in order to make a stereo microphone, two microphones are encased, put at a 45 degree angle, but have to be bi-directional. This placement is also referred to as X-Y setup or Blumlein Pair.
Due to this configuration the sound is like and exact replica of an orchestra instead of a one man band. Another approach to this technology is called the MS or Middle-Side Technique. This technique involves one element to be bi-directional and the other omni-directional. The bi-directional records all sound except for the center area and the omni records everything. This results in sound first moving through the bi-directional component and then through the omni component giving you the feeling of which direction the sound is coming from. If the sound comes from either side the signal is louder than any instrument that makes noise from the center.
The sound differences are separated into channels to maintain the sound difference of the two sides and are played back on right and left speakers. Imagine listening to a band that sounds like the noise only comes from one person and not all members of the band. The sound you hear would not have enough fluctuations in sound waves for your ears to hear the audio levels each instrument and vocal are actually producing. The performance would be just like karaoke instead of professional. This is why stereo microphones are needed to produce optimal sound performance.