In this free video tutorial, Production Expert Team member Julian Rodgers demonstrates a simple method for testing the polarity of mics.
Sometimes Plosives Are A Good Thing
We usually spend our time trying to keep plosives out of our mics. But the big, low-frequency bump caused by the diaphragm being displaced by a plosive can be used as an indication of the electrical polarity caused by the diaphragm being displaced away from you.
Just the lightest puff of air is all that's needed, the important thing is that it starts quickly so there is a pressure wave that hits the diaphragm rather than a gradual blow. If you try this, here are some pointers:
- Don't monitor the mics! - you don't want to send your speaker drivers jumping across the room. You're not interested in what it sounds like, just what it looks like.
- Switch out High Pass Filters - obvious but worth saying.
- Don't hold the mic too close - 6-8 inches is fine. The inverse square law is in effect here so if you pop gently from up close, that's the same as doing it really hard from further away.
- Respect delicate mics - A dynamic won't care how it gets treated, modern condensers can take loads of abuse. Ribbons are strictly at your own risk. I don't recommend this for ribbons but not all ribbons are the same and some modern ribbons are far tougher than they used to be. With care, I'd happily use this technique on my sE VR2 but I wouldn't do it to my Coles 4038s.
Tricky Examples Where This Technique Helps
There is always the possibility that the phase can get reversed on its journey from the mic to the recorder. Incorrectly wired cables. Mismatches between gear which is wired pin 2 hot and pin 3 hot. There are lots of possibilities. In the video, I give two examples of cases where testing the polarity of a mic has thrown up unexpected results.
The first is the case of a mic with what I refer to as a logo in the "marketing position" - on the back of the mic so the logo is clearly visible in the publicity shot with the singer and the logo in shot.
The second is the case of a homemade sub kick made from a speaker driver. Testing the polarity of a speaker driver is easy using an AA battery but the polarity of speakers and mics is opposite - after all, they are doing the opposite of each other!
Try this technique, you probably won't find any surprises but if you've never checked you'll never know. Just don't go wrecking any vintage ribbons!