Microphone

A microphone is a device that converts sound waves—small variations in air pressure—into electrical signals. These signals can then be amplified, recorded, or transmitted. Microphones are fundamental components of many audio communication and production technologies, including telephony, broadcasting, music recording, speech recognition, and surveillance.

History of the Microphone

Although one of the earliest microphone designs was developed by Johann Philipp Reis in the 1860s, his device was unable to clearly transmit speech.

• In the 1870s, Elisha Gray and Alexander Graham Bell designed microphones based on the liquid conductor principle; Bell achieved the first intelligible voice transmission in 1876 and secured the patent rights.
• In 1878, David Edward Hughes developed the first carbon microphone using carbon granules. Thomas Edison further improved this technology, inventing the durable carbon microphone used in telephones.
• Advancements in radio broadcasting and recording technologies during the 1920s led to improvements in carbon microphones; electromagnetic and condenser microphones also became widespread during this period.
• In the 1930s, ribbon microphones emerged, and with the use of strong magnets, microphones became smaller and more durable. New technical solutions were developed in condenser microphones to prevent interference caused by humidity.

Today, research continues on new technologies such as microphones compatible with high sampling rates, ambisonic systems, and optical microphones. In the future, optomechanical and laser-based microphone technologies are expected to play a significant role in the microphone industry.

Types of Microphones

Microphones are classified according to their method of converting acoustic energy into electrical signals. The main types include dynamic, condenser, and ribbon microphones, along with several specialized varieties.

Dynamic Microphones

Dynamic microphones operate based on electromagnetic induction. A coil attached to the diaphragm moves within a magnetic field, generating an electrical current. Due to their low sensitivity and robust construction, they are widely used for high sound pressure level (SPL) sources such as live vocals, drums, and guitar amplifiers. Dynamic microphones do not require an external power supply.

Condenser Microphones

Condenser microphones (also known as capacitor microphones) detect changes in capacitance between a diaphragm and a fixed backplate, converting these changes into electrical signals. Their high sensitivity and wide frequency response make them preferred in studio environments for vocals, acoustic instruments, and ambient sound recording. They are usually powered by 48V phantom power or an internal battery.

They have two subtypes:

• Large diaphragm condenser microphones are popular for vocals and instruments, emphasizing bass or midrange frequencies.
• Small diaphragm condenser microphones are suitable for sources with fast transients and high-frequency detail (e.g., cymbals, strings).

Ribbon Microphones

Ribbon microphones use a thin metal ribbon suspended within a magnetic field. Sound waves move this ribbon, changing the current passing through it. These microphones are bidirectional (figure-eight polar pattern) and provide a smooth, natural tone. Due to their delicate construction, they require protection from physical damage, and some older models are sensitive to phantom power.

Other Types

• Electret Microphones: A subtype of condenser microphones using permanently charged materials; commonly used in consumer electronics like mobile phones and computers.
• USB Microphones: Typically condenser or dynamic microphones with built-in digital converters and audio interfaces, allowing direct connection to computers.
• Tube Microphones: Condenser microphones employing vacuum tubes for signal amplification; they add warmth and character to the sound.
• Crystal Microphones: Use piezoelectric materials; not intended for high-quality audio but for specific applications.
• MEMS Microphones: Microelectromechanical systems developed for compact digital audio recording in mobile devices and computers.

Advantages and Disadvantages

Choosing a microphone type requires balancing sensitivity, durability, frequency response, and suitability for the acoustic environment.

Polar Patterns

Microphones have different polar patterns that define their sensitivity to sound arriving from various directions. These patterns are critical for microphone placement and isolating unwanted sound sources.

• Cardioid: The most common directional pattern. It picks up sound primarily from the front while largely rejecting sounds from the sides and rear. Suitable for close-miking vocals and instruments.
• Supercardioid and Hypercardioid: Narrower versions of the cardioid pattern; they provide tighter sound pickup from the front but allow slightly more sound from the sides and rear. Require precise positioning.
• Omnidirectional: Picks up sound equally from all directions. Preferred for natural and realistic recordings; useful when the speaker moves around (e.g., lavalier microphones).
• Bidirectional (Figure-Eight): Picks up sound equally from the front and rear while rejecting sounds from the sides. Used in stereo recording techniques such as Blumlein and mid/side.
• Shotgun: Provides a very narrow and focused pickup from the front, largely rejecting side and rear sounds. Used in film, broadcasting, and outdoor recording to capture sound from a distance.