What difference does polar pattern make? Actually, probably none. Look at the mics in your mic cupboard. I'll bet they are all cardioid! So you don't even have the option.
Cardioid is way out in front as the most common polar pattern, and that's because it is by far the most useful.
A cardioid mic, if you need a reminder, is sensitive to the front and sides but not at the back. An omnidirectional mic is almost equally sensitive all round. A figure-of-eight mic is equally sensitive at front and back but not at the sides. A hypercardioid mic is sensitive at the front but there is a small unwanted lobe of sensitivity at the rear.
So the great advantage of the cardioid compared to the rest is that you can easily point it away from sound sources you don't want to pick up. This could be other instruments, the audience in a live recording, or just the ambience or reverberation of the room.
In 'How to record a 50-strong choir and piano accompaniment with just five mics', one of the objectives was to place mics for the piano that wouldn't also pick up the choir. This is to give more flexibility in mixing.
Clearly these microphones should be directional, and cardioid mics would give the best separation between piano and choir. Hypercardioid mics would work too, given a little attention to their unwanted rear pickup.
So, picking up the sound you want and not picking up the sound you don't want is a clear reason to consider polar patterns.
But there are other reasons too…
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If you want a really clean-sounding mic, then you should choose a 'native' omnidirectional or figure-of-eight. By 'native' I mean a mic that is built to that pattern, not a multipattern mic that is switched to it.
It is simpler for a manufacturer to design an omnidirectional or a figure-of-eight mic. Cardioid and hypercardioid patterns are created by blending the DNA of omnidirectional and figure-of-eight. Frankenstein would have been proud.
Having said that, microphone manufacturers have pretty much conquered the 'in between' patterns of cardioid and hypercardioid. Even so, it is a worthwhile listening experience to try native omnidirectional and figure-of-eight mics. The sound is just that little bit more pure.
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OK, subjective sound quality. All directional mics, meaning mics that are not omnidirectional, show an increase in low frequency response when the mic is close to the sound source. This is often known as the proximity effect.
The proximity effect is clearly less than natural. On the other hand it does produce a nice warmth.
You could, for instance, record the lead vocal of a song with a cardioid, and record the background vocals with omnis. The contrast in tonal quality will separate them nicely.
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One more reason…
Using only cardioid mics is like a violin player only playing on one string.
A violin has four strings, and we have four basic polar patterns. We should become virtuoso users of them all, otherwise we can't really claim to have mastered recording technique.
So in conclusion, if your microphone kit is over-balanced towards cardioids, which I bet it will be, then you owe it to yourself to invest in the alternative patterns.
And useful though multipattern mics are, they are not quite the same, nor so satisfying, as mics that are natively omnidirectional, figure-of-eight and hypercardioid. such as the little beauties in the photo above, from the Sennheiser MKH range. (The MKH50 is supercardioid rather than hypercardioid, which is a little less focused, but has reduced unwanted rear sensitivity.)
Let us know your experiences with polar patterns. We would love to hear.