Unable to find out why your microphones are not producing the best sound? Don’t know how to optimize the quality of your recordings? Whether be it in live sound situations, or in studio recording sessions, you need to know how to properly use microphones. Hence, the question that you should be asking is – What is “Microphone Polar Patterns”?
In today’s awesome article (I think it’s going to be!), we will cover the various concepts surrounding the subject of microphone polar patterns. Understand what they actually do, and how they affect audio recording in general. Find out why some patterns are more suitable for certain applications, and others are not. So, let’s not waste any more time and start learning!
Introduction – What are they?
Polar patterns are essentially a microphone’s directionality, which indicates its sensitivity to sound waves coming from different angles around its central axis. Polar pattern diagrams are designed to show the locus of points that produce the same level of audio signal output in a microphone, if a determined sound pressure level (SPL) is being generated from that specific point.
Take note that a microphone’s design is what determines its physical body’s orientation, in relation to the polar pattern diagrams. For microphones with large diaphragms such as the “Oktava 319”, the upward direction that is depicted in the polar diagram, is typically perpendicular to the microphone’s body. This is commonly referred to as “side fire” or “side address”.
As for microphones with much smaller diaphragms such as the Shure SM58, the diagram typically shows the extension of the polar pattern, coming from the axis of the microphone. Also referred to as “end fire” or “top/end address”. Microphone designs will sometimes include a combination of multiple principles in producing the intended polar pattern.
These design principles often range from “shielding” (meaning diffraction/dissipation/absorption) by the housing itself to the electronic combination of dual membranes.
Let us now look at the various types of polar patterns:
- Shotgun microphones
Also known as “nondirectional”, an Omnidirectional microphone’s pick-up is usually understood to be a perfect three-dimensional sphere. In real world applications however, this is not accurate. Just like most directional microphones, an omnidirectional microphone’s polar pattern is a function of frequency.
The microphone’s body will of course, not be infinitely small. Thus, this causes a destructive interference to sounds coming from the rear, resulting in a slight flattening of the polar response. As the microphone’s diameter increases (assuming it’s cylindrical), reaching the wavelength of the affected frequency, the flattening will also increase accordingly.
Hence, a microphone with the smallest diameter will provide the best omnidirectional attributes at high frequencies. Unlike cardioids, omnidirectional mics do not use resonant cavities as delays. Thus, they are considered to be the most transparent mics, as they don’t heavily colour the original sound. Being pressure-sensitive, it is possible for them to produce a flat low-frequency response down to 20 Hz or lower.
These types of microphones are largely sensitive to sounds arriving from only a single direction. Unidirectional mics will face upwards in its polar patterns diagrams. Professional diagrams will depict the sound intensity for various frequencies, plotted at angles radially from 0 to 360 degrees. More simplified diagrams will only show an overview of pattern shapes, and their names.
Here are the different types of unidirectional polar patterns:
The cardioid microphone is arguably the most used in the audio industry. The name comes from its “heart-shaped” sensitivity pattern, i.e. a cardioid. Microphones under the cardioid family are often used for vocal or speech applications, as they are excellent in rejecting sounds from other directions. In 3D form, the cardioid is apple-shaped, centred around the microphone which acts as the “stem” of the apple.
Cardioid microphones reject most sounds coming from the side and rear, minimizing the chances of feedback from the monitors. Since directional microphones produce their patterns based on pressure gradient sensing, placing them too closely to the sound source (around a few centimeters) results in a boost of the low frequencies due to the increased gradient.
This phenomenon is called the “proximity effect”. The Shure SM58 Dynamic Microphone has been in the live sound industry for over 50 years. It is very often used for vocal applications in live concerts, all over the world. This demonstrates the importance and popularity of dynamic cardioid mics.
Hyper and super-cardioid
A hyper-cardioid microphone is similar to a cardioid mic, but designed to have a slightly larger figure-8 pattern, ultimately producing a more narrow and “tighter” area of sensitivity at the front. It also has an additional small lobe of sensitivity at the rear.
A super-cardioid mic is very similar to a hyper-cardioid, but with stronger front sensitivity and weaker rear sensitivity. Various patterns (between omni and figure-8) can be achieved by adjusting their mix. But standard explications state that a hypercardioid is produced with a 3:1 ratio combination, producing nulls at 109.5°, while supercardioid is created with a 5:3 ratio, with nulls at 126.9°.
Also known as “Figure 8”, these microphones are equally sensitive to sound coming from both front and back of the element. They are designed to not respond to sound pressure, but only to the pressure difference between front and back. Sound coming from the sides do not produce any pressure difference, as they reach both front and back equally. Thus, there is no sensitivity to sound from the sides.
If we look at it mathematically, omnidirectional microphones are considered as scalar transducers (responds to pressure from all directions) and bi-directional microphones are vector transducers (responds to the gradient along an axis normal to the plane of the diaphragm). It is important to take note that most ribbon microphones are designed with a bi-directional polar pattern.
Widely known as the highest directional microphone of simple first-order unidirectional designs, shotgun microphones have a polar response of a hypercardioid at lower frequencies. However, they have an increased forward sensitivity at medium and higher frequencies due to an interference tube. This causes a cancellation of sound waves (that are off-axis) entering the longitudinal array of slots.
Using this technique does have its set-back, as it can produce some colouration to the original sound. This is due to the presence of some rear lobes that changes in level and angle, depending on the frequency that is affected. Because of their very narrow forward sensitivity, shotgun microphones are generally utilized on television and film productions, in stadiums, and for outdoor recording of wildlife.
Alright folks! That would be all I have to offer for you people today. Hopefully you can now experiment with the different types of microphone polar patterns, and use them in your productions!
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