Dynamic, condenser and boundary microphones
Microphones differ in how they turn sound into voltage, and that decides a lot: sensitivity, noise, ruggedness, and how they sound.
Dynamic microphones
A diaphragm moves a coil in a magnetic field (moving coil) or a thin metal ribbon in a field (ribbon). Motion induces a voltage.
- No power needed, very rugged, handles loud sources.
- Low sensitivity (around 1 to 3 mV/Pa) and a modest high-frequency response, because the moving mass is relatively large.
- Ribbons are naturally figure-8 and have a smooth, soft top end, but are delicate and sensitive to blasts of air.
Condenser microphones
The diaphragm and a fixed back plate form a capacitor. Sound changes the distance between them and therefore the capacitance, which a small amplifier converts to voltage.
- Higher sensitivity (5 to 50 mV/Pa) and a wide, detailed frequency response, because the diaphragm is very light.
- Needs power: 48 V phantom power, supplied through two 6.8 kΩ resistors over the signal lines, or a separate supply.
- Electret capsules hold a permanent charge, so only the amplifier needs power. Used in small and low-cost microphones.
- RF condensers use the capacitance to tune a radio-frequency oscillator instead of a polarising voltage, which makes them less sensitive to humidity.
Large and small diaphragms
| Large diaphragm (about 25 mm) | Small diaphragm (about 12 mm) | |
|---|---|---|
| Noise | lower self-noise | higher self-noise |
| Pattern | less consistent across frequency | more consistent, more precise |
| Use | voice, close sources | stereo pairs, instruments, measurement |
A large diaphragm also makes the pattern more directional at high frequencies, and shapes the character of off-axis sound.
Boundary microphones
A boundary (or pressure zone) microphone sits flat on a surface, with the capsule only a few millimetres from it. Direct sound and the reflection from the surface arrive almost together, so there is no comb filtering from the surface. It is useful on stages, tables and floors. Two designs exist, one with an omni capsule near the surface and one with a plate arrangement that gives a directional response. The low-frequency cutoff depends on the size of the surface.
Choosing
- Loud and rough sources, live use: dynamic.
- Detail and quiet sources: condenser.
- Stereo pair for acoustic music: matched small-diaphragm condensers.
- Fixed in a room or on a stage, unobtrusive: boundary.
Draft: written by an AI assistant, awaiting technical review.
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