10 Varieties of Microphones

Sound is an extraordinary phenomenon. Every noise we perceive is a result of tiny fluctuations in air pressure. What’s remarkable is how effectively the air carries these changes, even over long distances, with such precision.

If you’ve studied How CDs Work, you’re familiar with the first microphone ever created. It featured a metal diaphragm connected to a needle, which etched a pattern onto metal foil. When someone spoke toward the diaphragm, the resulting air pressure changes moved the diaphragm, which then moved the needle, recording the sound on the foil. Later, running the needle over the foil would generate vibrations that would move the diaphragm, recreating the sound. This purely mechanical system demonstrates the power of air vibrations.

All contemporary microphones aim to achieve the same goal as the original models, but through electronic rather than mechanical means. The purpose of a microphone is to transform varying air pressure waves into fluctuating electrical signals. There are various technologies employed to achieve this conversion. Continue to the next page to explore different types of microphones, including one of the first invented by Alexander Graham Bell.

10: Liquid Microphone

Liquid microphones, created by Alexander Graham Bell and Thomas Watson, were among the earliest functional microphones developed and paved the way for the later condenser microphone. These early devices consisted of a metal cup filled with water and sulfuric acid, with a diaphragm placed over the cup and a needle positioned on the opposite side. When sound waves hit the diaphragm, they caused the needle to move within the liquid. A small electrical current passed through the needle, which was modulated by sound vibrations. Though the liquid microphone was never highly practical, it served as a fascinating science experiment.

9: Carbon Microphone

The simplest and oldest microphone utilizes carbon dust. This technology was used in the first telephones and continues to be used in some telephones today. A thin metal or plastic diaphragm rests on one side of the carbon dust. As sound waves hit the diaphragm, they compress the carbon dust, altering its resistance. Running a current through the carbon changes the current flow as the resistance varies. These microphones are still employed in mining and chemical industries because higher voltage lines could trigger explosions.

8: Fiber Optic Microphone

Fiber-optic systems, which utilize incredibly thin glass strands to transmit data instead of traditional metal wires, have significantly impacted the telecommunications industry, including microphone technology. So, why is this important? Unlike traditional microphones, which are often bulky and transmit electrical signals, fiber-optic microphones are extremely small and suitable for electrically sensitive environments. Additionally, they can be manufactured without metal, making them invaluable in magnetic resonance imaging (MRI) applications and other scenarios where radio frequency interference is a concern [source: Fibersound Audio].

7: Dynamic Microphone

A dynamic microphone utilizes the principle of electromagnetism. When a magnet passes over a coil of wire, it generates an electric current in the wire. In the dynamic microphone, sound waves move the diaphragm, causing either a magnet or a coil to shift. This motion produces a small current. This microphone type is most effective when placed near a vocalist or instrument, capturing sound from no further than a foot away.

The modern dynamic microphone is typically the design that most people envision: a slim, tubular body with a circular recording head on top. These mics are ubiquitous in live music performances and karaoke due to their blend of reliability, portability, and excellent sound quality.

6: Electret Microphone

Electret microphones are among the most commonly used microphones globally. Due to their low cost and simplicity, they are found in devices such as cell phones, computers, and hands-free headsets. An electret mic is a type of condenser microphone that replaces the external charge with an electret material, which is naturally polarized electrically. These microphones are also popular in documentary and news production, often used as tiny, discreet lapel mics that can be clipped to a subject's clothing [source: BeStar Acoustic Components].

5: Ribbon Microphone

A ribbon microphone uses a thin ribbon, typically made from aluminum, duraluminum, or nanofilm, suspended within a magnetic field. As sound waves pass, they cause the ribbon to move, altering the current that flows through it. These microphones are bidirectional, meaning they capture sound from both sides of the mic.

The RCA PB-31 was one of the pioneers of ribbon microphones, introduced in 1931. It made a significant impact on the audio and broadcasting industries by setting a new benchmark for clarity. Other manufacturers, such as BBC-Marconi with their Type A and ST&C Coles 4038, produced similar models shortly after.

Ribbon microphones lost popularity after the early radio era, as they were replaced by more durable dynamic and condenser models. The delicate ribbon inside made them highly fragile, often requiring repairs even from the slightest bump. Despite this, modern studios occasionally use ribbon mics when they desire a true "vintage" sound.

4: Laser Microphone

A laser microphone captures vibrations from surfaces, such as a windowpane, and converts them into an audio signal. When sound strikes the surface, it causes the surface to bend, which in turn bends the laser beam. This bending is then translated into sound using a photocell. Recently, a new type of laser microphone has been developed, which works by passing smoke across the laser beam aimed at a photocell, ideal for espionage due to its ability to detect sound over great distances, though it’s not suited for regular audio recording.

3: Condensor Microphone

A condenser microphone operates as a capacitor, where one of the plates moves in response to sound waves. This motion alters the voltage between the plates, and the resulting changes are amplified into a detectable signal. To function, condenser mics typically require a small battery to maintain a voltage across the capacitor, although many modern consumer models can draw power directly from a USB connection to a computer.

Condenser microphones are popular in recording studios, available in two types: large diaphragm and small diaphragm. Large diaphragm mics are favored for recording vocals and instruments producing deep bass or mid-range frequencies. Small diaphragm mics, more compact in design, are excellent for capturing higher-frequency sounds such as those from string instruments or cymbals.

2: Microelectromechanical Microphone

The microelectromechanical microphone (MEMS) is an advanced version of the electret design and is becoming increasingly popular in devices like smartphones and headsets. These tiny microphones, measuring just a few millimeters across, house a microchip with a mechanical diaphragm for sound capture, a capacitor to convert the sound into electrical current, an amplifier to boost the signal, and a digital converter to turn it into audio data for use in digital devices.

1: Crystal Microphone

Certain crystals exhibit a change in electrical properties as they shift shape, like the phenomenon in quartz watches. When a diaphragm is attached to a crystal, the interaction with sound waves produces a signal. Though cheap to produce, crystal mics were eventually replaced by better-quality condenser and dynamic mics. They now find limited use in applications such as monitoring and automotive transmitters and sensors.

As demonstrated, almost every conceivable technology has been utilized to transform sound waves into electrical signals. The common element among them all is the diaphragm, which captures the sound waves and initiates movement in the system, generating the electrical signal.