In our brief examination of the recording chain front end, the microphone, it's good not to forget what follows the microphone. In the same way a phono cartridge requires a phono preamplifier to process and amplify the signal—and we all know how important to sound quality the phono preamplifier is in the chain—so too do microphones.
Both microphones and phono cartridges are mechanical transducers that convert motion into electrical energy. In the case of a microphone it is converting changes in air pressure while with phono cartridges it is the motion of the needle tracing the plastic grooves in the vinyl.
Both transducers have very low output and must be amplified before you can play them back on a reproduction system or place them into an A/D converter to record them.
And, just like with moving coil and moving magnet cartridges, different microphone types have varying output levels that require more or less amplification.
If we break down the main microphone types into three categories they would be: condenser, ribbon, dynamic.
By far, the most common and preferred microphone type used today is the condenser microphone (like the U67, Telefunken, and Gefell I wrote about already). Condenser microphones operate using an electrically-charged diaphragm placed close to a backplate. When sound waves hit the diaphragm, the distance between the diaphragm and backplate changes, causing capacitance variations that generate an electrical signal. Somewhat the opposite of an electrostatic loudspeaker.
Ribbon microphones are today mostly relics used for specific duties in recording studios. They utilize a thin strip of metal (usually aluminum) suspended between two magnets. When sound waves hit the ribbon, it vibrates, inducing a small electrical current proportional to the sound waves. These are amazing on horns and blaring instruments.
Dynamic microphones are everywhere. They are versatile, handle huge dynamics, have low cost, and are most widely used in live performances as well as specialized applications in the studio (like high dynamic applications such as drums). If you ever attended a school function in the auditorium it's likey you were listening to some administrator drone on through one of these. They operate using a diaphragm attached to a coil of wire suspended within a magnetic field. When sound waves hit the diaphragm, it vibrates, causing the coil to move within the magnetic field and generate an electrical signal.
All three types of microphones, like phono cartridges, must be amplified by a preamplifier before we can use them to record or listen through a PA system.
In the case of the condenser types, they need two stages of preamplification. In the same way a moving coil cartridge requires the additional gain boost of a head amp, condensers do as well. This "head amp" is built into the condenser microphone and receives power either through its connecting cable. In most condensers the external power needed to run their internal head amp comes from what is known in the industry as "phantom power". In pro applications this is 48V DC. In consumer versions that connect via USB, it is +5V and inside the microphone is included an A/D converter and amplifier. In the case of the Neuman U657 and the Telefunken stereo, the vacuum tube head amp in the microphone body receives its power from an external box where the higher voltage power supply is located.
Tomorrow, the microphone preamplifier.
