A condenser microphone is a microphone that converts sound into an electrical signal by means of a capacitor, formed by a thin, movable diaphragm and a fixed backplate. Among microphones, it is valued for its high sensitivity, extended frequency response and accurate transient detail, which makes it the standard choice for studio vocals, acoustic instruments and many measurement and broadcast tasks.
Because the capacitor must be charged and its tiny signal buffered, a condenser microphone needs a power source, usually 48 V phantom power supplied by the mixer or audio interface. This requirement and its delicate diaphragm distinguish it from the robust, passive dynamic microphone.
How a condenser microphone converts sound
The capsule consists of a diaphragm a few micrometers thick, typically gold-sputtered polyester film, stretched in front of a perforated metal backplate. The two plates form a capacitor holding a fixed electrical charge, so when sound pressure moves the diaphragm, the changing gap changes the capacitance and therefore the voltage across the plates.
That voltage change is the audio signal, but it comes from an extremely high source impedance. A built-in impedance converter, either a field-effect transistor or a vacuum tube, buffers the signal and drives the microphone cable. Because the diaphragm is so light, it follows fast transients and high frequencies more closely than the heavier moving coil of a dynamic microphone.
The charge on the capsule can be supplied in different ways, as the table shows.
| Type | How the charge is supplied | Typical character |
|---|---|---|
| True condenser (externally polarized) | Polarizing voltage from phantom or external supply | Classic studio design, very low noise |
| Electret condenser | Permanently charged material in the capsule | Compact, low cost, common in lavaliers |
| Tube condenser | External supply, tube as impedance converter | Dedicated power unit, often a warmer sound |
| RF condenser | Capsule in a high-frequency oscillator circuit | Robust against humidity |
Large-diaphragm and small-diaphragm designs
Condenser microphones are commonly grouped by diaphragm diameter, which strongly shapes their sound and polar behavior. The boundary is informal, but capsules of about 1 inch (25 mm) are called large-diaphragm and those of about 1/2 inch (12 mm) or less are called small-diaphragm.
| Property | Large-diaphragm | Small-diaphragm |
|---|---|---|
| Typical diameter | About 25 mm | About 12 mm or less |
| Self-noise | Often very low, about 5 to 12 dB-A | Usually somewhat higher |
| Off-axis response | Changes noticeably with angle | More consistent with angle |
| Typical sound | Present, often flattering | Neutral and precise |
| Common uses | Vocals, voice-over, solo instruments | Acoustic guitar, overheads, ensembles |
Many large-diaphragm models offer switchable polar patterns by combining two capsules back to back. Small-diaphragm pencil microphones are favored for stereo pairs, because their consistent off-axis response keeps the stereo image accurate.
Condenser microphones compared with dynamic and ribbon types
The three main transducer types trade sensitivity against robustness in different ways. A condenser captures the most detail but also captures the room, background noise and every small movement of the performer.
| Type | Transducer | Needs power | Sensitivity | Typical strengths |
|---|---|---|---|---|
| Condenser | Capacitor | Yes | High | Detail, transients, high frequencies |
| Dynamic | Moving coil in a magnet | No | Low | Durability, high sound pressure, live stage |
| Ribbon | Thin metal ribbon in a magnet | Passive models no | Low | Smooth top end, figure-8 pattern |
Lavalier and shotgun microphones are usually condenser designs as well, because small capsules and high sensitivity are essential for those applications. Their use cases differ, but the underlying transducer principle is the same.
Key specifications and how to read them
Condenser specifications describe how quiet, how loud and how sensitive the microphone is. Together they define the usable dynamic range and how much preamplifier gain will be needed.
| Specification | Typical range | What it means in practice |
|---|---|---|
| Sensitivity | About 10 to 40 mV/Pa | Higher values need less preamp gain |
| Self-noise | About 5 to 20 dB-A | Lower values suit quiet sources |
| Maximum SPL | About 120 to 150 dB SPL | Level before distortion rises |
| Pad | Often -10 or -20 dB | Prevents overload with loud sources |
| Phantom power | 48 V, a few mA | Must be enabled on the input |
Practical use and common mistakes
Condenser microphones reward careful placement and a quiet room, because they reveal both. Typical vocal setups place the singer about 15 to 30 cm from the capsule, with a pop filter in between.
- Recording in an untreated room: the microphone captures reflections and background noise as clearly as the voice.
- Forgetting phantom power: the microphone produces no signal, or a weak, distorted one.
- Overloading the capsule or preamp: loud drums or guitar amplifiers call for the pad or more distance.
- Plosives and handling noise: without a pop filter and shock mount, breath bursts and stand vibrations reach the recording.
- Humidity and condensation: moisture on the capsule can cause crackling, so microphones should acclimatize before use.
A non-technical view
A condenser microphone has an extremely thin, light skin inside. It moves with even the faintest sound. Because it is so light, it picks up breaths and the shimmer of a guitar string. Heavier microphones tend to smooth these tiny details over.
That sensitivity comes with two conditions. First, it needs a small amount of electrical power to work. Second, it also hears the room, the traffic outside and the computer fan. It shines in a quiet space, which is why it is the usual choice in recording studios.
A concrete example
A podcast producer sets up a large-diaphragm condenser microphone in a small spare room for a narrated series. The first test recording sounds hollow, because hard walls send reflections back into the capsule, and the meter shows a noise floor near -55 dBFS from a desk fan.
The producer hangs heavy blankets behind the speaker, switches off the fan, places a pop filter and positions the speaker about 20 cm from the microphone with the cardioid pattern selected. Phantom power is enabled on the audio interface and the gain is set for peaks around -12 dBFS. The new recording has a noise floor below -70 dBFS and a close, intimate voice that needs very little processing.