What Are A Microphone's Polar Patterns?
Each and every microphone made today has what is known as a polar pattern, but what exactly is this? Though it may sound a little complicated, a polar pattern simply describes a microphone's inherent directionality. In more specific terms, polar patterns refer to the sensitivity of any given microphone to sounds arriving from different angles, to its central axis.
Let's take a look at a pictorial example. When you view an image of a microphone's polar pattern, what you're looking at is a top-down view of a microphone, facing forwards. In the image - a typical case - zero degrees marks the front of the microphone, 180 the back, with the left and right edges found at 270 and 90 degrees respectively. Each circumference of the circle, from the outside to the inside, represents a 5-decibel (dB) reduction in audio sensitivity.
As we can see, the shape of the polar pattern touches the outermost circle at zero degrees, falling below -5 dB at the 90 and 270 decibel points. This indicates that the microphone is more than 5 dB less sensitive at its sides, as opposed to the front.
Looking towards the rear of the microphone, we can see that the sensitivity continues to decline incrementally right up until the very back is reached, complete with a zero dB reading. In theory, this means that the no sound should be captured from the rear of the instrument.
Using a polar pattern to make the finest choice
Once a you've developed a good understanding of polar pattern image, you'll quickly and easily be able to visualise any given recording microphone's directionality. Therefore, you'll be able to utilise this information to help you choose the most suitable microphone possible for your next audio session. Moreover, you'll be able to recognise both the most and least sensitive areas of a microphone's polar pattern - this can help you make informed decisions with regards to microphone placement, to both maximise the capture of a sound source's desired output, and minimise the capture of unwanted sound.
Remember, though a microphone might sound incredible in practice, if the polar pattern is not going to complement the desired sound source or recording environment, it may not be the most suitable one for your needs.
One of the best ways of using polar patterns to isolate certain sound sources, while minimising others that may be nearby, is the surprisingly common practice of micing up to a drum kit. What do we mean by this? Stay tuned for a upcoming post, where we will discuss this activity in greater detail.
Read on for a concise explanation of some of the most commonly used polar patterns across the RØDE microphones range.
Directional polar patterns
The cardioid polar pattern is the most common of the directional polar patterns - this is the one featured in the example above. So-named because the response resembles a heart shape (hence, cardio), it's widely used when there is a need to focus on one sound source, simultaneously reducing pick-up from the sides and rear.
A simple example of this would be a vocalist on stage, giving a live performance with a handheld microphone. A cardioid polar pattern would be highly effective at capturing the singer's voice, but would also block out other sounds form the fold back monitors and other performers on the stage.
A pair of cardioid microphones held together at a 90 degree angle to one another can create the commonly used stereo technique known as X/Y. This approach can give a separate left and right capture of the sound source, and features prominently on RØDE's NT4 microphone and Stereo VideoMic range. This technique, among others, will be analysed in greater depth in a forthcoming article.
Hyper-cardioid and super-cardioid polar patterns
These two polar patterns are, of course, variations of the classic cardioid shape, but with a tighter directionality at the front. They also pick up smaller levels of sound from the rear and sides off the capsule, if in close proximity. This characteristic must be factored in, if either of these cardioid polar patterns are apparent.
The shotgun microphone is the most extreme example of a directional device, with a particularly narrow front pick-up area - sounds from all other sides will by largely ignored. The longer the line tube of a shotgun microphone, the tighter the polar pattern will be. These specific type of microphone are most commonly used in film and television sets, where it is necessary for sound to be picked up from a distance. Sports events and wildlife documentaries also harness the capabilities of the shotgun microphone.
Bidirectional (figure-of-eight) polar pattern
Bidirectional microphones, also known as figure-of-eight devices, pick up an equal level of sound from the front and the rear, but sound from the side is blocked out, hence the '8'-shaped polar pattern. These microphones will result in a highly realistic sound duplication, as you're capturing more of the natural ambience of the recording space, alongside the sound source. The RØDE NTR Ribbon Microphone, as with all devices of this type, features the figure-of-eight polar pattern.
These particular microphones are also used in the popular 'Blumlein' and 'mid/side' stereo recording techniques. Figure-of-eight microphones will be further discussed in greater detail in an upcoming article, which will also cover recording techniques and stereo arrays.
Omnidirectional polar pattern
Omnidirectional microphones pick up sound from all directions in a perfect sphere, resulting in an incredibly natural and realistic audio recording. Typically, omnidirectional microphones include lavalier and headset varieties, as they allow the talent to move their head naturally without altering the overall sound of the recording.
When you come to choose your RØDE microphone, be sure to take a look at the polar pattern graphics, found in the specs section for each device. These will help you choose the perfect microphone for your needs.
Keep an eye on the RØDE blog for more exciting upcoming articles - in the near future, you can learn all about microphone placement, selection and recording techniques.