Microphones are a subset of a larger group of devices called transducers, which convert energy from one form to another. In this article, we will take a closer look at condenser microphones to learn how they change acoustic energy to electric energy.
How Do They Work?
You are probably most familiar with the housing of a microphone. It’s the hard outer casing part of the microphone that you can see. It often has a wire frame mesh to protect the inner workings (called the capsule or element) of the microphone.
For a condenser microphone, the capsule is where the transduction magic happens. In the capsule there are two components layered closely together. One is the backplate and the other is the diaphragm. The backplate is a piece of electrically conductive material (often gold-sputtered mylar or metal foil) fixed in place. The diaphragm—which is a thin electrically conductive membrane—is attached to the capsule so it is free to move. Both the backplate and the diaphragm are electrically charged, which creates a capacitor. (Capacitors are circuit components made of two plates that store charge.) The size of the charge between the backplate and the diaphragm remains constant so long as neither one moves.
As pressure waves travel through the air into the microphone, the diaphragm moves, changing its distance from the backplate. This changes the capacitance, or stored charge, between the diaphragm and backplate, a difference which is output as an electrical signal. From there, the signal goes through a circuit to ensure it is strong enough and clear enough to be sampled and manipulated by the computer, mixer, or data acquisition system at the other end of the cable.
All of this is only possible so long as there is an electrical charge provided to the capsule. Thus, all condenser microphones require a power source. Most condenser microphones use batteries or phantom power. Phantom power is an electrical power supply delivered to the microphone along the same cord that carries the microphone signal (the power rides the same cord as the signal like a ghost in the background). This power is absolutely essential to condenser microphones to maintain the charge between the membrane and backplate.
Is a Condenser Microphone Right for Me?
Because the diaphragm is relatively light, condenser microphones tend to have greater sensitivity than other types of microphones. They also have a wider flat frequency response and a better transient response than other microphones, making for cleaner recordings.
Some potential cons for condenser microphones include the need for a power supply and a typically higher purchasing price than other microphones. Some condenser microphones, called electret microphones, have a permanent charge on the backplate or the diaphragm to overcome this problem. The word electret is an amalgamation of the words electricity and magnet. Essentially, an electret has a dielectric material that keeps a permanent charge. Electret condenser microphones are popular in cell phone, laptop, and other small consumer electronic applications.
Condenser microphones may also struggle more in extreme temperature or humidity conditions. Like all equipment, it is important to make sure that the microphone you are using is meant for a given task. A wide range of microphones are available, and most microphones come with a specifications and guidance for optimum use. If you have questions about what microphone to use for an application, most manufacturers have recommendations and specs available for their products online.
Although condenser microphones are used often in research labs and recording studios, they are not meant for all applications. Sometimes a dynamic microphone is better suited to your application. Read more about dynamic microphones here.