A microphone is fundamentally a transducer — it converts acoustic energy (sound waves in air) into electrical energy (voltage variations in a wire). Every microphone on the market uses one of a handful of underlying principles to accomplish this conversion, and understanding these principles is essential for making informed purchasing decisions and getting the best recordings possible.
Dynamic Microphones: Robust and Versatile
Dynamic microphones work on electromagnetic induction. A lightweight diaphragm — typically made of plastic film coated with a thin layer of aluminum or copper — is attached to a coil of wire suspended in a magnetic field. When sound waves push the diaphragm back and forth, the coil moves within the magnetic field, generating a small alternating voltage according to Faraday's law of electromagnetic induction.
The classic Shure SM58 remains one of the most recognizable dynamic microphones in live audio. Its frequency response of 50Hz to 15kHz with a presence peak in the 2-5kHz range makes it exceptionally good at capturing the critical midrange of vocals while rejecting the low-frequency rumble that causes feedback on stage. The SM58's cardioid polar pattern — which picks up sound primarily from the front and rejects from the sides and rear — is carefully engineered to provide consistent rejection across its operating range.
What makes dynamics attractive for live use is their durability. There are no fragile electronics, no delicate diaphragm under tension, no phantom power required. You can drop a dynamic mic, step on it, and it keeps working. This ruggedness comes with a trade-off: dynamics are less sensitive than condensers, meaning they produce lower output voltage for the same sound pressure level. This requires more preamp gain — and more preamp gain means more self-noise in the signal chain. For studio applications where the sound source is close-miked and controlled, this limitation matters. For live vocals in front of a loud band, it's irrelevant.
The Beyerdynamic M201 and Shure SM7B are examples of dynamics that work exceptionally well in studios. The SM7B's extended bass response and smooth high-end made it the de facto standard for broadcast voiceover and podcasting for decades, despite its low output requiring high-gain preamps. Understanding when to use a dynamic versus other types is often the difference between a recording that cuts through a mix and one that gets buried.
Condenser Microphones: Detail and Precision
Condenser microphones use electrostatic rather than electromagnetic transduction. The diaphragm in a condenser mic is typically a thin metal or metal-coated polymer film stretched very tightly over a metal backplate, forming a capacitor. When sound waves deflect the diaphragm, the distance between diaphragm and backplate changes, altering the capacitance. This change in capacitance, when a polarising voltage (or in electret designs, a permanent charge) is applied, produces a proportional change in output voltage.
The Neumann U87 is perhaps the most famous condenser microphone in recording history. Its large-diaphragm capsule produces a detailed, open sound that works on everything from vocals to acoustic guitar to room ambience. The U87 offers multiple polar patterns — cardioid, omnidirectional, and figure-8 — making it versatile for stereo recording techniques and different mic placements.
Condenser microphones require external power to operate the active electronics in the microphone body. "Phantom power" (+48V) is the standard method, supplied by mixing consoles and microphone preamps through the same XLR cable that carries the audio signal. The phantom power standard (IEC 61938) delivers 48 volts through pins 2 and 3 of the XLR connector, with pin 1 as ground. This is why you see the "48V" button on microphone preamps and audio interfaces.
Small-diaphragm condensers like the AKG C414 or Neumann KM184 are workhorses for acoustic instruments. Their extended high-frequency response, fast transient reproduction (the ability to accurately capture rapid changes in sound pressure), and consistent polar pattern across their frequency range make them ideal for capturing the attack of guitar strings, the breath of woodwinds, and the complex overtones of percussion. In orchestral recording, matched stereo pairs of small-diaphragm condensers are standard for coincident and near-coincident stereo techniques.
Ribbon Microphones: The Natural Sound
Ribbon microphones use a thin strip of metal foil — usually aluminum, typically less than 3 microns thick — as both diaphragm and conductor. This strip is suspended between the poles of a magnet, and when sound waves move the ribbon, it cuts through the magnetic field, generating a voltage. The ribbon's bidirectional polar pattern (figure-8) is a natural consequence of its design: both sides of the ribbon are exposed to sound pressure, with the front creating positive pressure on one side and negative on the other.
The RCA 77DX and Coles 4038 are classic ribbon designs from the 1930s-1950s that are still used in professional recording today. Their warm, smooth high-frequency response and natural rejection of off-axis sound make them flattering on brass instruments, electric guitar cabinets, and string sections. Ribbon microphones don't have the presence peaks that condensers often exhibit — instead, they reproduce transients with less edge, creating a sound that many engineers describe as "natural" or "vintage."
Modern ribbon microphones like the Royer R-121 and AEA R84 address the fragility concerns of vintage designs. The R-121's ribbon is physically tougher and can handle higher sound pressure levels than older ribbons, making it suitable for close-miking electric guitar cabinets at volumes where older ribbons would have been damaged. The figure-8 pattern of ribbon microphones is also useful in studio recording: by placing the microphone so the null (least sensitive axis) points toward a problematic reflection or nearby instrument, you can achieve isolation that a cardioid condenser couldn't match from the same position.
Polar Patterns: Coverage and Rejection
A microphone's polar pattern describes its sensitivity to sound arriving from different angles. Cardioid (heart-shaped) microphones pick up primarily from the front, with rejection at the sides and least sensitivity at the rear. This makes cardioid mics useful for live sound because they can be pointed at a performer while rejecting stage monitors and audience noise from behind. The hypercardioid and supercardioid patterns are tighter variations with slightly more rear sensitivity but greater reach from the front.
Omnidirectional microphones pick up sound equally from all directions. In studio recording, omnis can produce a more natural, open sound because they don't exhibit the off-axis coloration that directional microphones introduce. The proximity effect — the bass boost that occurs when a directional mic is placed close to a sound source — is also absent with omnis. However, omnis are rarely used in live sound because they offer no rejection of feedback-causing reflections.
Figure-8 patterns (like ribbon microphones produce naturally, and large-diaphragm condensers can electronically emulate) are bidirectional, picking up from front and rear while rejecting from the sides. This is useful for mid-side stereo techniques, where a figure-8 microphone combined with a cardioid produces a fully adjustable stereo image. It's also useful in studio recording for recording two performers facing each other with the microphone between them.
Choosing the Right Microphone
For live vocal applications, a dynamic cardioid microphone like the Shure SM58 or Sennheiser e835 remains the professional standard. These microphones handle high sound pressure levels, resist feedback, survive touring, and don't require phantom power. The investment in a quality dynamic vocal mic pays dividends in reliability night after night.
For studio vocal recording, the choice depends heavily on the vocalist and genre. A large-diaphragm condenser like the Neumann U87 or AKG C414 is a versatile starting point that works across genres. For particularly aggressive vocal styles, a dynamic like the SM7B or a robust ribbon can handle high SPLs without the condenser diaphragm distorting. For breathy, intimate vocal styles, a small-diaphragm condenser with extended high-frequency response might capture the desired detail.
Instrument recording applications are equally varied. Electric guitar cabinets are commonly close-miked with dynamic microphones (SM57 on the speaker cone, Royer on the cabinet outside) or ribbon microphones for a less harsh, more natural representation. Acoustic guitars benefit from small-diaphragm condensers positioned to capture both the picking detail and the body resonance. Drum overheads are typically matched pairs of small-diaphragm condensers. Kick drums are often captured with a dynamic inside the drum combined with a large-diaphragm condenser or ribbon outside.
The best approach is to develop familiarity with a range of microphones and trust your ears. Technical specifications like frequency response charts and polar pattern diagrams are useful guides, but nothing replaces listening tests in your specific acoustic environment with your specific source material. Build your microphone collection thoughtfully, and resist the temptation to use the same microphone on everything — the best engineers match microphone to application with deliberate intention.