Microphone

A microphone, often called a mic or mike, is a special tool that changes sounds into electrical signals. This helps us talk, listen, and enjoy music in many ways. Microphones are used in phones, hearing aids, computers, and many other devices that need to pick up sound.

There are several kinds of microphones, each working a little differently. One common type is the dynamic microphone, which uses a coil of wire near a magnet. Another is the condenser microphone, which uses a moving part to change sound into electricity. There are also contact microphones that use special crystals to do this job.

Before a microphone’s signal can be recorded or played back, it usually needs to be connected to a preamplifier. This small device makes the signal strong enough to be used. Thanks to microphones, we can share our voices and music all around the world.

History

People needed ways to speak to larger groups, so they used devices like theater masks with horn-shaped openings to make voices louder. These early tools helped actors in big spaces be heard.

Later, inventors created devices that could send sound over wires. In 1856, Antonio Meucci made a device with a moving coil of wire in a magnetic field to create electric signals from sound. In 1876, Alexander Graham Bell and Elisha Gray used a liquid design for early telephones, but the sound quality was not very good. The first good voice telephone microphone was the carbon microphone, invented by David Hughes and later improved by Thomas Edison. This helped create better telephones, broadcasting, and recording.

In 1916, a new type called the condenser microphone was made, and in 1923, the moving coil microphone was built. The ribbon microphone was also introduced in 1923. In 1949, the Neumann U 47 set a new standard for recording sound in studios. As television and film grew, new microphones like the shotgun microphone in 1963 were developed for better directionality. The Shure SM57, made in 1965, became very popular for recording instruments and live music because of its clear sound and durable design.

Varieties

Microphones come in many types, each working in a different way to turn sound into an electrical signal. They can be used for things like phone calls, recording music, and more.

Condenser

The condenser microphone uses a special part called a capacitor. When sound waves hit it, the distance between two plates changes, which creates an electrical signal. These microphones are known for their high quality and are often used in studios for recording music. They need a small amount of power to work.

Dynamic

Dynamic microphones work by moving a small coil inside a magnet when sound hits it. This movement creates an electrical signal. These microphones are tough, don’t get damaged easily by moisture, and are popular for live performances.

Ribbon

Ribbon microphones use a thin metal ribbon that moves inside a magnetic field when sound hits it. This movement creates an electrical signal. These microphones are good at picking up sound from both sides and are often used in recording studios.

Carbon

The carbon microphone was one of the first types of microphones. It uses granules of carbon that change how much electricity flows through them when sound presses on them. These microphones are very strong but don’t sound as good as newer types.

Piezoelectric

Piezoelectric microphones use special materials that create electricity when they are pressed by sound waves. These are often used in devices like drum triggers and underwater recording.

Fiber-optic

Fiber-optic microphones use light to turn sound into an electrical signal. They are good for places where other microphones might not work well, like inside machines that create strong magnetic fields.

Fabry-Pérot interferometer-based microphones

These are a special kind of fiber-optic microphone that uses light bouncing between two mirrors to detect sound. They can pick up very faint sounds and are used in scientific research.

Laser

Laser microphones use a laser beam to detect how a surface moves when sound hits it. This can be used to pick up sounds from far away.

Liquid

Early microphones used water to turn sound into electricity. These were not very practical for everyday use but were important in the history of telephones.

MEMS

MEMS microphones are tiny chips that can be built into many modern devices. They are a type of condenser microphone and are very common in phones and computers.

Plasma

Plasma microphones are experimental and use a stream of ionized gas. Sound changes the gas, which changes the electricity flowing through it.

Speakers as microphones

Sometimes, speakers can be used as microphones because they work in a similar way. They are not as good for picking up high-quality sound but can be useful in simple devices like walkie-talkies or video game chat systems.

Capsule design and directivity

The way a microphone is built affects how it picks up sound. A pressure microphone uses a diaphragm to sense sound pressure from all directions, so it hears sounds equally from every side. A pressure-gradient microphone has a diaphragm that is open on both sides, which lets it pick up sounds more from the front and back and less from the sides. When sounds come from the front and back at the same time, this type of microphone doesn’t detect much difference. This creates a special pattern called a figure-8. Other designs mix these two ideas to change how the microphone hears sound. Shapes and extra parts can also change how well a microphone picks up sounds from different directions.

Polar patterns

A microphone's directionality, or polar pattern, shows how sensitive it is to sounds coming from different angles. The diagrams above show how the microphone picks up sound from various directions.

An omnidirectional microphone picks up sound equally from all directions. Unlike other types, it doesn’t use special designs to change sound direction and works well for low frequencies. These microphones are often used in studios, churches, and TV interviews.

A cardioid microphone is shaped like a heart and mainly picks up sound from the front while reducing sound from the sides and back. This makes it great for singing and speaking. Other types, like hypercardioid and supercardioid, have tighter front sensitivity. Bi-directional microphones pick up sound equally from the front and back but ignore sound from the sides.

Shotgun microphones are very good at picking up sound from one specific direction using a long tube. They reduce unwanted noise but can sometimes pick up sounds from behind, affecting audio quality.

Main article: Boundary microphone

Application-specific designs

A lavalier microphone is designed for hands-free use. These small microphones are worn on the body and can be attached to clothing with a clip, pin, tape, or magnet. The cord can be hidden under clothes and connected to a receiver in a pocket or directly to a sound system.

A wireless microphone sends audio as a radio or optical signal instead of using a cable. Most professional wireless microphones use a small radio transmitter to send the signal to a nearby receiver.

A contact microphone picks up vibrations directly from a solid surface. This type of microphone can detect very quiet sounds, like those made by small objects or insects.

A throat microphone picks up speech directly from a person's throat, allowing use in noisy environments.

A parabolic microphone uses a curved reflector to focus sound waves onto a microphone, similar to how a parabolic antenna works with radio waves. These microphones can pick up sounds from far away and are used for nature recording, sports events, and other purposes.

A stereo microphone combines two microphones in one unit to create a wider sound. These are often used for broadcast or field recording.

A noise-canceling microphone is designed for noisy places. They are used in aircraft and live concerts to help make voices clearer by reducing unwanted sounds.

Stereo microphone techniques

Different methods are used with microphones during live shows, recording in studios, or filming movies. By placing one or more microphones in the right way, we can capture the sounds we want and avoid unwanted noise.

Powering

Many microphones need power to work, especially those with special parts inside. Early microphones used a different power source and a special cable. Later, as technology improved, the power needed became smaller, and the same cable could carry both sound and power.

In the 1960s, new ways to power microphones were created, mostly in Europe. Two main methods were developed: one called T-power and another called phantom power. Today, phantom power is used more often because it works for both powered and unpowered microphones. In devices like cameras and camcorders, a method called plug-in power is often used, which works with a small cable connector. These power methods are described in an international standard.

Connectors and connectivity

Microphones use different types of connectors to connect to other devices. Common connectors include:

• Male XLR connector on professional microphones
• 1⁄4 inch (or 6.35 mm) phone connector on less expensive musician's microphones
• 3.5 mm (or 1⁄8 inch) TRS mini phone plug on prosumer camera, recorder, and computer microphones
• USB for direct connection to computers

Some microphones use other connectors, such as a 5-pin XLR or mini XLR, for portable equipment. Lavalier (or lapel) microphones often use a special connector for wireless transmitters, like a radio pack. Since 2005, professional-quality microphones with USB connections have become available for direct recording into computer software.

The AES42 standard, published by the Audio Engineering Society, defines a digital interface for microphones. Microphones that follow this standard send a digital audio stream through an XLR or XLD male connector instead of an analog signal. These digital microphones can be used with new equipment that supports the AES42 standard or through a special interface box. Studio-quality digital microphones are now available from several manufacturers.

Measurements and specifications

Microphones are made differently, so they respond to sound in their own special ways. This can change how they pick up sounds of different pitches and loudness. While scientists like microphones that respond the same way to all sounds, musicians often like microphones that change the sound in interesting ways.

There are rules about how to describe microphones, but not all companies follow the same rules, so it can be hard to compare them. One way to show how a microphone picks up different pitches is with a chart that shows its sensitivity from low to high pitches. Another important measure is how quiet a microphone can pick up sounds, which is called its noise level. Lower numbers mean the microphone can pick up very quiet sounds. There is also a level where the microphone cannot pick up sounds any louder without changing the sound badly, called the clipping level. The range between the quietest and loudest sounds a microphone can pick up is called its dynamic range. Sensitivity tells us how well a microphone changes sound into an electrical signal, with higher numbers meaning it can pick up sounds better.

Measurement microphones

Some microphones are made to test speakers and measure noise levels. These microphones are carefully made to give accurate results and come with a paper that shows how accurate they are.

These microphones can hear sounds from all directions and are used to measure how loud a sound is. To measure sound intensity or power, scientists often use two or more of these microphones together or special tools called hot-wire anemometers.

Calibration

Main article: Measurement microphone calibration

To use a microphone for science, we need to know exactly how sensitive it is. This can change over time, so these microphones need to be checked regularly. Companies and labs that test equipment can do this checking. All checking goes back to special tools at places like NPL in the UK, PTB in Germany, and NIST in the United States.

Depending on what they are used for, these microphones need to be tested often, like every year, or after something bad happens, such as being dropped or hearing sounds that are too loud. Most come in special cases to protect them.

Arrays

A microphone array is a group of microphones working together. These arrays are used for many helpful purposes. They can pick up voices from background noise, like in phones or hearing aids. They are also used for surround sound and to find where sounds are coming from, such as locating airplanes. Arrays help make very clear recordings and can focus on specific sounds in a three-dimensional space.

Windscreens

See also: Pop filter

Windscreens, also called windshields, help reduce the effect of wind on microphones. Pop-screens protect against wind coming from one direction, while foam covers shield wind from all directions. Blimps, zeppelins, and baskets fully enclose the microphone, protecting it from wind vibrations that can create noise.

The material used for these screens—such as wire gauze, fabric, or foam—is designed to let sound waves pass through easily while blocking stronger wind. Thicker materials block more wind but can also affect high-frequency sounds. The space between the screen and the microphone also helps reduce wind noise. Smooth surfaces and materials like artificial fur can further reduce turbulence and noise.

Various microphone covers

Two recordings being made—a blimp is being used on the left. An open-cell foam windscreen is being used on the right.

Dead cat and a dead kitten windscreens. The dead kitten covers a stereo microphone for a DSLR camera. The difference in name is due to the size of the enclosure.