Two microphones with the same "front" sound can behave in opposite ways in a real room. The difference lies in directionality, that is how sensitive the microphone is to sounds arriving from the sides and from behind. The graph that describes it is called a polar pattern, and knowing how to read it helps you choose a microphone and, above all, place it.
How to read a polar pattern
The diagram is a circle seen from above, with the microphone at the center. Zero degrees is the direction the microphone "faces", the front; 180 degrees is the rear. The plotted curve shows sensitivity in each direction: where the curve touches the outer edge sensitivity is highest, where it pulls in toward the center the microphone picks up less.
The concentric circles usually represent attenuation steps of 5 or 10 dB. Many spec sheets show several curves for different frequencies, because directionality is not the same in the lows and the highs.
The main patterns
Omnidirectional
Picks up sound almost equally from every direction. It is the most natural pattern and has no proximity effect, but it records a lot of room. It works well in rooms with good acoustics, for recording a group around a table or as a clip-on mic on clothing, where the source is very close.
Cardioid
The curve is heart-shaped: sensitive at the front, less at the sides, very little at the back. The point of least sensitivity, called the null, is at 180 degrees. It is the most common pattern for voice and podcasts, because it reduces sounds coming from behind the microphone.
Supercardioid and hypercardioid
Narrower than cardioid at the front, they reject the sides better. In exchange a small lobe of sensitivity appears at the rear, and the nulls move to the sides, around 120-130 degrees for a supercardioid. They are useful when other sources are nearby, as in a podcast with several people seated at the same table.
Figure-8 (bidirectional)
Equally sensitive front and back, nearly deaf at the sides. The rear is in opposite polarity to the front. It is typical of many ribbon microphones and some multi-pattern condensers. It is used to record two people facing each other with a single microphone, or in specific stereo techniques.
Summary table
| Pattern | Sensitive to | Nulls | Typical use |
|---|---|---|---|
| Omni | All directions | None | Room, lavalier, groups |
| Cardioid | Front | Rear (180°) | Voice, podcasts, instruments |
| Supercardioid | Narrow front | About 125° | Several nearby voices |
| Figure-8 | Front and rear | Sides (90°) | Two people, stereo |
Placing the microphone using the nulls
The most useful way to exploit a polar pattern is to aim the nulls at noise sources.
- Cardioid and computer: if your PC has a noisy fan, position the microphone so the computer sits directly behind it. The noise arrives in the least sensitive zone.
- Supercardioid and window: with a supercardioid the deafest point is not directly behind but at an angle. Rotate the microphone until the noisy window falls in that direction.
- Figure-8 and street: if the noise comes from one side, a figure-8 oriented with its sides toward the source attenuates it very well, provided there is no reflective wall close behind the microphone.
Headphones and monitors
In a podcast participants often listen on headphones. If someone uses speakers or open-back headphones at high volume, the sound coming out is picked up and creates echo. Pointing the nulls toward the speakers reduces the problem, but closed-back headphones remain the best solution.
Directionality changes with frequency
No real microphone follows the ideal pattern at all frequencies. Many cardioids become nearly omnidirectional in the lows and narrower in the highs. This explains why low-frequency noises, such as a fridge hum or heavy traffic, are picked up even from behind.
Another consequence is off-axis coloration: someone who moves to the side while speaking doesn't just get quieter but also duller. In my work I always ask whoever is recording to stay in front of the microphone and, if they tend to move, I prefer a model with a more even off-axis response.
Multi-pattern microphones
Some dual-diaphragm condensers let you select the pattern with a switch. They are versatile and handy for experimenting: you can record the same voice in cardioid and in omni and compare how much of the room gets into the recording.
In short
- A polar pattern shows how sensitive the microphone is in each direction.
- Cardioid for voice, supercardioid with several nearby sources, omni for room and lavalier.
- Figure-8 picks up front and back and rejects the sides.
- Aiming the nulls at noise sources is the most effective placement technique.
- Directionality varies with frequency: bass almost always arrives from behind as well.
