Choosing a microphone is the decision that most affects the sound of a home recording, more than the software and often more than the audio interface. The two big families are dynamic and condenser microphones. Neither type is better in absolute terms: there are situations where one or the other works better.
How a dynamic microphone works
In a dynamic microphone a thin membrane, the diaphragm, is attached to a small coil sitting in a magnet's field. When sound makes the diaphragm vibrate, the coil moves and generates a weak electrical voltage by induction. It is the same principle as a loudspeaker, in reverse.
Typical characteristics:
- needs no power;
- is rugged, withstanding knocks, humidity and high sound pressure;
- has low sensitivity: it produces a weak signal and needs a lot of gain from the preamp;
- responds less to detail in the extreme highs and to fast transients, because the diaphragm and coil have more mass.
How a condenser microphone works
In a condenser microphone the diaphragm is one of the two plates of a capacitor: the other is a fixed backplate placed very close to it. When the diaphragm vibrates, the distance between the plates changes and so does the capacitance. An internal circuit converts these variations into a signal.
This design requires power, usually 48 V phantom power supplied by the interface through the XLR cable. Some models, called electret, have a permanent charge and use power only for the internal circuit.
Typical characteristics:
- high sensitivity: less gain is needed;
- great detail in the highs and on transients;
- picks up a lot of the room too: reflections, fans, traffic;
- more delicate with knocks and humidity.
Large and small diaphragm
Large-diaphragm condensers are the classic studio vocal mics; they tend to have a full sound and low self-noise. Small-diaphragm ones are often used on acoustic instruments for their accurate response, even off-axis.
Practical comparison
| Aspect | Dynamic | Condenser |
|---|---|---|
| Power | None | 48 V phantom or electret |
| Sensitivity | Low | High |
| Room noise picked up | Little | A lot |
| Detail in the highs | Moderate | High |
| Ruggedness | Very high | Medium |
| Gain required | High | Moderate |
Proximity effect
Many directional microphones, dynamic and condenser alike, show proximity effect: the closer the source, the more the bass increases. Used well, it makes a voice warm and "radio-like"; used badly, it makes it muddy and boomy. Moving a few centimeters changes the result a lot, so it pays to find a distance and stick to it.
Which to choose at home
Untreated room, background noise
A dynamic used a few centimeters from the mouth is almost always the safest choice. It picks up little of the room and puts the voice up front. The downside is the high gain required: some budget interfaces add hiss at maximum gain. In those cases there are small inline amplifiers that provide extra gain before the interface.
Quiet, treated room
A large-diaphragm condenser delivers a more open, detailed voice. But without acoustic treatment it will record the wall reflections just as precisely, making the voice sound "boxy".
Acoustic instruments
Guitar, piano and strings generally benefit from a condenser's detail.
Very loud sources
Guitar amps and drums are often recorded with dynamics, which handle high sound pressure without difficulty.
USB microphones
USB microphones build the preamp and converter into the microphone body. They are convenient for getting started, but limit expansion: you can't easily use two USB microphones together and you can't change the preamp. In my work I find them fine for meetings and simple recordings, less so for a multi-voice podcast.
In short
- A dynamic is rugged, not very sensitive and picks up little room: ideal in untreated spaces.
- A condenser is sensitive and detailed, requires phantom power and a quiet room.
- Proximity effect boosts bass up close: find a distance and keep it.
- A dynamic needs a lot of gain: check that your interface provides it without hiss.
- USB microphones are handy for starting out but hard to expand.
