Blog
Song path: Recording: Cardioid Microphones
Written by Andy Patterson
In the Abubilla studio we have a variety of microphones, which do different things in different ways. Microphones are transducers – they convert one type of energy into another – so acoustic energy into electrical energy. They work in an opposite way to loudspeakers, which convert electrical energy to acoustic energy. You can actually use a speaker cone as a microphone, but more on this in another edition of the song path.
The way each of these microphones work is different, and as a result this affects the amount of sound they pick up.
One way in which they differ is in their directivity or ‘Polar Pattern’. This describes how sounds which come from different directions will be picked up by the microphone. This is a useful indicator, as you can use the directivity of the microphone to plan your recording and how different sounds are picked and recorded.
The first pattern we are going to look at is CARDIOID.
As the word suggests, it is shaped a little like a heart, but has also been compared to the shape of an apple without the stalk.
So, in the case of the microphone shown here, we can see the heart shape. The back side of the mic (or the cleft of the apple) can be seen to be very good at rejecting sound. So you can use this to your advantage. If there is something reasonably close to something else and you want to maximise the pickup of one sound source over that of another, you could aim the back of the microphone at the unwanted sound source and cut down on the amount that is recorded. In an anechoic chamber, the rejection would be very good, but remember in real world situations, there will be reflections of the sound source that come into the microphone at different angles, and so there will not be complete rejection, but it can help to achieve the separation you need.
The Shure SM58 microphone has a very good off axis rejection, which is why it is used extensively in Live sound for vocals – the back of the microphone often pointing downwards at monitor speakers, which have a sloping front to project the sound towards the listener – and hence the microphone as well.The SM58 also has a good inbuilt pop shield – to screen out plosives. The other cardioid microphones we have in the Abubilla studio include the Røde NT5, the AKG C214 and the C414 (which has switchable directivity patterns).
One effect that you must be aware of with directional microphones is that of the ‘Bass-tip up’ or ‘proximity’ effect. This is due to the way the microphones are constructed to ensure their directivity. It results in an increase in the low frequency response of the microphone when it is close to the sound source. This must be taken in to account when mic’ing sound sources.
We’ll look at the other microphones and their uses soon.