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Cardioid Microphone Pickup and Polar Pattern

Cardioid Microphone Pickup and Polar Pattern

A simple explanation of a cardioid pickup pattern for a microphone.



Microphones that have a pickup pattern referred to as cardioid are great for picking up sound directly in front of them but rejecting noise from the sides and rear, sometimes also referred to as unidirectional. The shape of the pickup pattern basically resembles a heart which is where the term cardioid comes from. Thanks to the microphones ability to focus on the noise coming from the front makes them an ideal microphone for use when ambient noise from the room is not wanted into the mix. As some of the ambient noise in the room is rejected by these microphones they can also be effective when trying to deal with feedback issues as the reflections of sound around the room can't get back into the microphone as easily as other microphone pickup types.

The cardioid pickup pattern does come with a slight downside whereby the proximity effect comes into play. The proximity effect is where bass response of the microphone is increased when the sound source is close to the microphone. This needs to be considered and could be detrimental to speech intelligibility if the person speaking is trying to use the microphone too close; this of course can be overcome by ensuring correct microphone technique.

Here's an image of the polar pattern for a cardioid pickup pattern microphone:


Polar Pattern - Cardioid

Looking at the polar pattern you can get a lot of good information about how the microphone is expected to perform but don't forget these readings would have been taken in an anechoic chamber so they are free from sound reflections.

If you look at the solid line on the left hand image and compared to the frequency legend underneath you will see that it refers to the 125Hz response of the microphone. The response of the microphone at that frequency produces an almost oval shape and does pick up some sound from the rear and the sides. Compare this to the 8000Hz frequency response of the right-hand image which is a lot more directional and you can see the microphone rejects most of the noise coming from the rear and sides. You can then decipher all the other frequencies in between by looking at the other lines on the chart. The 500Hz and 1000Hz lines will show the most relevant shape to the cardioid description.

One final thing to note about these charts is how to read the graph lines. Looking at the 0 point this is the response directly on axis to the microphone head and will be the most sensitive point. As you move around clockwise our anti-clockwise you will reach the 30 degrees off axis and then onto the 60 degrees off axis etc. If you look at the 90 degrees off axis measurement for the 500Hz frequency line you will see that it is a distance in from the edge. Each segment of the circular graph is a 5dB reduction in response sensitivity; this can be derived by looking at the numbers above the 0 measurement on each line. So, follow the chart round to 90 degrees, look in until you find the line require for the frequency you're looking at, see which segment it lands on and deduct that amount of level from the expected response.

Hopefully that all makes sense, but we'll cover it again on other pickup patterns soon.


   
Created On  5 Feb 2018 9:13  -  Permalink

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