In order to make the most of your recordings, it is important to understand the basic principles of polar patterns. Because not understanding it could make or mar the entire recording process. The directional or polar pattern of microphones is what determines the sensitivity of the microphones from different angles. That is to say, the polar patterns define the amount of signal from different directions that can be picked up by the microphone.
By choosing the right pattern, you can prevent unwanted sound sources from filtering into the signal entering your microphone. It also helps you to adjust the mix between the ambient and room sound, or it can change the frequency response as well as influencing the proximity effect.
How to read a polar pattern diagram?
First off, you may need to be able to read polar pattern diagrams correctly. It contains the necessary information that is needed to anticipate your recording results. Imagine a 360° field surrounding a microphone. The 0° mark lies at the front of the microphone and it is the angle at which the microphone is at maximum sensitivity. The circle scale consists of smaller circles, each representing a reduction in sensitivity of about 5 dB.
The decibel (represented as dB) is a logarithmic unit for comparing two values. So, should the specifications of a cardioid microphone indicate a rear rejection of 25 dB, this means that the most sensitive part is (0 °) and the least sensitive part (180 °) and they are being compared.
For pressure (sound), the current and voltage are +6 dB twice as high as the signal strength, +20 dB generates 10 times more signal. A more conventional rear rejection for the cardioid pattern is around -20 dB. So, the sound that comes from behind the microphone can be picked at a sensitivity of 1/10 when compared to the front signal.
What is an omnidirectional polar pattern?
1. Captures sound from every angle
The omnidirectional pattern is one in which sounds are captured from every angle. It captures sound from any direction. This is because it has the same sensitivity to sound pressure in any direction.
2. Low sensitivity to wind or handling noises
An omnidirectional pattern offers the flattest frequency response, best bass reproduction, and is less sensitive to wind or handling noise when compared to other polar patterns.
3. Not suitable for low sound room recordings
When recordings are made in a low sound room, the result may not be as satisfying as expected. In recording situations where the sound picked up are to be played using a PA (e.g. concerts), the feedback may be an issue.
4. Smaller diameter better for higher frequencies
Because the microphone body is not infinitely small, it tends to be in its own way when sound from the rear is to come in. This, therefore, can result in a slight flattening of the polar response. It increases when the diameter of the microphone (assuming it is cylindrical) approaches or reaches the wavelength of the frequency in question. What this means is simply that microphones with the smallest diameter offer the best omnidirectional properties at high frequencies.
When to use an omnidirectional microphone
- If you’re recording sound from a wide source, e.g. room tone, outside ambiences, an orchestra, a choir, a band or even a grand piano.
- When you’re recording a moving target, e.g. an acoustic guitarist who wouldn’t standstill.
Pros of an omnidirectional microphone
- Immune to proximity effect
- There is lower self-noise
- A frequency range which generally extends a full octave lower
- Less coloring of off-axis sounds
- The last pro is particularly true for omnidirectional microphones with small diaphragms. For this reason, small diaphragm microphones are the most accurate measurement microphones ( e.g Earthworks microphones).
Cons of using an omnidirectional microphone
- it can pick up unwanted sounds (this effect is generally expected and may be intentional)
If you want to record something very specific and eliminate ambient noise, an omnidirectional microphone may not be the best choice for you.
Pay attention to your recording environment and avoid background noise as much as possible to avoid unwanted noise.