How Do Microphones Work?
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They’re such a big part of lives now that you probably don’t realize how often you encounter a microphone every day. Whether you’re hearing an announcement in a public space, listening to music, or even watching a video on your phone, microphones play a very big part in the spaces we visit and the media we consume.
While they’re very essential aspects of performance and recording, a lot of us don’t know how microphones work or what differentiates one from the other. And despite microphone technology constantly changing throughout the years, the basics we need to know have stayed the same. From learning the basics of how microphones work and what differentiates microphone types from each other, here’s what you should know about microphones and how they capture sound.
How Do Microphones Work?
Microphones are a type of transducer or a device that converts energy from one form to another. Microphones convert sound waves or acoustical energy into electrical energy, also known as the audio signal. Amplified and sent to a loudspeaker or headphones, the sound picked up by the microphone transducer should come out from the speaker with no significant changes.
While different types of microphones have different ways of converting energy, they all have a diaphragm. The microphone diaphragm is an extremely thin piece of material, often paper, plastic, or aluminum, which vibrates when incoming sound waves from a sound source hit it, causing other components in the microphone to vibrate. These vibrations are then converted into an electrical current which becomes the audio signal.
Impedance
Microphones have an electrical characteristic called impedance, measured in ohms that depend on the design. Low impedance is considered fewer than 600 ohms, medium impedance is considered between 600 ohms and 10k ohms, and high impedance is above 10k ohms.
Most professional microphones are low impedance or about 200 ohms or lower. Low impedance microphones can drive long cables with a less high-frequency response and are more resistant to hum and radio-frequency interference.
Low-impedance microphones are often preferred over high-impedance input, as using a high-impedance microphone with a long cable will result in loss of high-frequency response signal due to the capacitance of the cable, and because long high-impedance cables tend to pick up more hum.
Types of Microphones and How They Work
Carbon Microphones
Carbon microphones were heavily used in the 20th century, and while there are different and more modern types of microphones today and with this microphone design is less common now, these microphones still find use thanks to their resilience.
Carbon microphones are usually suspended by metal coils, with a metal housing with holes cut out to protect the internals while letting sound through. A layer of carbon granules is sandwiched between two metal plates, or the microphone diaphragm and the backplate. A voltage across the metal plates causes a current through the granules and, as the microphone diaphragm moves back and forth, it alters the pressure and resistance of the granules, creating a low-quality electrical signal.
Dynamic Microphones
Dynamic microphones are best used when the volume is too high and ambient noise is uncontrollable, such as in live events or large spaces. Dynamic microphones can also be used for recording musical instruments like snare drums and guitar amps due to it needing more electrical energy to make the microphone diaphragm move back and forth.
A dynamic microphone works when sound waves hit the diaphragm of the microphone and make it move back and forth along with the coil. When the coil moves within the magnet’s magnetic field, it creates an electrical current. This current travels through the coil onto the recording device. Like with other types of microphones, the current will vary in strength based on the pitch and volume of the sound.
Most dynamic microphones are cardioid mics, meaning that the microphone is made to capture from one side of the capsule. Dynamic microphones with a super-cardioid pattern are also preferred for many live vocals since their directional properties are better than cardioids.
Moving-Coil Dynamic Microphones
A moving-coil dynamic microphone is versatile and ideal for general-purpose use. This type of microphone is a simple design with few moving parts. This audio equipment is quite durable and resilient to rough handling, making it great for stage performances and touring.
They are robust, relatively inexpensive, resistant to moisture, and often wireless microphones that are usually better suited to handling high sound pressure, such as from close-up sound, certain musical instruments, and amplifiers. Moving-coil dynamic microphones generally have no internal amplifier and do not require internal batteries or external power.
With the moving-coil microphone, the diaphragm moves due to sound, which in turn makes the coil vibrate and creates an electrical signal. The oscillation of the electrical conductor within the permanent magnetic field causes an AC voltage to be produced across the coil via electromagnetic induction. This AC voltage is taken via lead wires as the mic’s audio signal.
Moving-Ribbon Microphones
Moving-ribbon microphones are a type of dynamic microphone that are extremely sensitive and are designed to be used for atmospheric types of sound, such as jazz, folk, blues, or more restrained vocals.
Active ribbon mics contain a thin ribbon of aluminum foil situated between two magnets. When the wire is moved within a magnetic field, a current is generated in the wire. When acoustical energy or sound waves hit the ribbon microphone, they convert sound and generate electrical energy or an audio signal. While almost every dynamic microphone is great for live events, active ribbon microphones are best used in the studio.
Think a dynamic microphone is exactly what you need as your own microphone? You can check out some of the best dynamic microphones on the market today right here.
Condenser Microphones
A condenser microphone is most often seen within the confines of recording studios and closed spaces where sound quality can be better controlled, and often need an external power supply to function.
Condenser microphones tend to be more sensitive and responsive to ambient sound and loud sound than dynamic microphones, making them useful for capturing subtle nuances and intricate details. A condenser microphone is not always ideal for high sound pressure as its high sensitivity can cause overload distortion in the mixing console and mic preamp.
Like most microphones, condenser microphones work by converting sound waves into electrical energy and often need to be connected to external power supplies. One of the most important parts of condenser microphones is the diaphragm, which moves according to the sound pressure difference between its front side and backside and moves in accordance with the sound waves it is subjected to, making this an essential part of the condenser microphone transducer.
Condenser mics and their capsules are designed as parallel-plate capacitors, with the movable diaphragm acting as the front plate in the capacitor while the backplate is stationary. When a sound wave hits the diaphragm of the condenser microphone, the diaphragm vibrates in close proximity to the backplate. The condenser capsule must be charged to capture sound properly. This is why all condenser mics require power to work and why the capsules have a very high impedance converter.
Electret Condenser Microphones
Moving coil microphones are the most commonly used type of dynamic microphone. These types of dynamic mics utilize a coil of wire attached to it. In a true condenser microphone, the electrical charge comes from phantom power. However, electret microphones use a different method for keeping the capsule charged. An electret material is one that carries a permanent electrical charge sealed within an insulating film. This means that no power is required to charge the microphone. However, external power may still be required to run the internal electronics of the microphone.
Phantom Power
Condenser microphones often need phantom power to function. This delivers a DC voltage to the microphone through the same shielded two-conductor cable that carries the audio from the mic.
For phantom power to function, the line between the power supply and the microphone must be balanced to the ground and uninterrupted by devices such as filters or transformers which might pass the audio signal but block DC power. Phantom power also requires a continuous ground connection from the power supply to the microphone.
Final Note
While a relatively new invention, microphones have become one of the most important pieces of audio equipment and sound systems in modern times. While there is more than one type of microphone out there today to suit different purposes, they all serve the same function of converting sound to be heard at its best. And now that you know just how each microphone works, you can now pick what you think suits your needs the most.
