Microphones
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Microphones are essential tools that convert sound waves into electrical signals, enabling the amplification, recording, and transmission of audio. Understanding their operation and components can help you select the right microphone for your application.
How Microphones Work
Microphones function as transducers, converting acoustic energy (sound waves) into electrical energy (signals). This process involves a diaphragm—a thin, flexible membrane—that vibrates in response to sound waves.
The various types of microphones, such as condenser mics or dynamic mics, transform sound waves into electrical signals in different ways, using different mechanisms.
Think of a microphone as a reverse loudspeaker. Just as a speaker converts electrical signals into sound, a microphone captures sound and turns it into electrical signals that can be amplified, recorded, or transmitted.
Microphone Components
Listed below are the components used in the most common types of microphones (dynamic and condenser mics). Each component plays a role in recording sound.
- Capsule: The capsule is the core of the microphone, housing the diaphragm and other parts that work with it. It serves as the area where sound waves are converted into electrical signals and has the greatest effect on the sound created by the mic.
- Diaphragm: A thin membrane that vibrates when struck by sound waves. Its movement is crucial for translating acoustic energy into electrical energy.
- Backplate (in Condenser Mics): In condenser microphones, the backplate is a charged component placed near the diaphragm, forming a capacitor. As sound hits the diaphragm, it creates variations in the distance between the diaphragm and the backplate. These variations are measured and translated into an electrical signal.
- Magnet (in Dynamic Mics): Provides a magnetic field in dynamic microphones. As the coil moves within this field, it induces an electrical current that mirrors the sound wave.
- Coil (in Dynamic Mics): Attached to the diaphragm, the coil moves within a magnetic field, generating an electrical current corresponding to the sound wave’s characteristics.
- Circuit: The signal from the microphone capsule is then sent through internal circuitry. This circuit processes the electrical signal generated by the diaphragm’s movement, preparing it for amplification or recording. The circuit consists of a transistor, transformer, and an analog output. The circuit and how it is constructed also affect the sound of the mic, but usually in a more subtle way, adding harmonic coloration to the core sound created by the diaphragm.
Dynamic vs. Condenser Microphones
Dynamic Microphones
Dynamic mics use the coil and magnet construction illustrated above to translate sound waves into an electrical signal. Sound waves move the diaphragm and coil, generating an electrical current.
They are more durable than condenser mics and are less sensitive. They can handle high sound pressure levels and do not require phantom power to operate.
Popular examples of dynamic mics are the Shure SM57, Shure SM58, and the Electro-Voice RE20.
Condenser Microphones
Condenser mics use the diaphragm and backplate construction illustrated above. Sound-induced diaphragm movements cause capacitance changes, resulting in an electrical signal.
Condenser mics require an external power source, often provided as phantom power, to maintain the electrical charge. Condenser mics are much more sensitive than dynamic mics and excel in capturing detailed sounds.
Popular examples of condenser microphones are the Neumann U87, Rode NT1, and the AKG C414.
Ribbon Microphones
Ribbon microphones are a special, delicate type of mic used primarily in studio recording. Ribbon mics employ a thin metal ribbon suspended within a magnetic field. Sound waves cause the ribbon to vibrate, inducing an electrical signal.
They are renowned for their natural, warm sound reproduction and bidirectional pickup pattern, capturing sound from the front and back while rejecting it from the sides.
Directional Characteristics and Polar Patterns
A microphone’s design and construction influence its sensitivity to sound from various directions, known as its polar pattern, sometimes referred to as a pickup pattern. Common patterns include:
- Cardioid: Sensitive to sound from the front, less so from the sides, and minimal from the back, resembling a heart-shaped area in front of the mic. This is the most commonly found polar pattern in mics. For example, most handheld and studio mics use a cardioid pickup pattern.
- Omnidirectional: Captures sound equally from all directions.
- Bidirectional (Figure-8): Captures sound from the front and back while rejecting it from the sides.
These patterns influence microphone placement and usage. For instance, a cardioid mic is ideal for isolating a vocalist from background noise, while an omnidirectional mic captures the sound of an entire space.
Other Factors Influencing Microphone Performance
Frequency Response
Frequency response indicates the output level of a mic across its entire frequency range. It affects how natural or unnatural the mic sounds, as well as its overall tonal quality and clarity.
Frequency response is measured by testing how the mic reacts to each frequency within the audible range (typically 20 Hz to 20 kHz).
Microphones with a “flat” frequency response are ideal when you want the most accurate, uncolored sound—such as in critical recordings or measurement situations. Others are voiced with purposefully boosted frequencies to add character, presence, or reduce muddiness and rumble.
Preamp
A microphone preamplifier (preamp) is essential for boosting the weak electrical signals produced by microphones to a usable level. In digital recording, preamps are most commonly found in audio interfaces that connect the mic to a computer. Without a preamp, most microphones, especially dynamic ones, would output signals too quiet for recording or amplification.
Preamps do more than amplify signals—they shape the sound. High-end preamps are designed to introduce minimal noise, preserving the microphone’s natural tone. In contrast, budget preamps may add hiss or unwanted distortion. Some preamps, especially those in analog consoles, add subtle harmonic coloration, contributing to warmth or brightness. Dynamic range also plays a role—high-end preamps offer better headroom, preventing distortion at high volumes.
Recording Environment
The environment in which you record significantly influences the quality of your audio captures. Factors such as room acoustics, ambient noise, and reflective surfaces can introduce unwanted sounds or distortions, affecting the clarity and fidelity of the recording.
Environment is a key factor in all recordings. A noisy, untreated environment can make a high-end microphone sound cheap.
Sensitivity
Sensitivity is a measure of how effectively a microphone converts sound pressure into an electrical signal, affecting how well it captures soft or distant sounds. Higher-sensitivity microphones produce stronger output signals for the same acoustic input compared to lower-sensitivity models.
Condenser mics are typically the most sensitive, making them suitable for capturing subtle nuances in quiet sound sources. Dynamic mics are typically less sensitive and therefore better suited for loud sound sources, such as guitar amplifiers or drums, where high sensitivity is unnecessary and could lead to distortion.