Crown Audio by Harman

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How to prevent feedback with a choir? Should I use large or small diaphragm mics?

I am the FOH mixer for a church and I read your article on strategies for miking choirs. One of the biggest problems I am facing is getting feedback before I reach a good level.  Also, would large- diaphragm mics accomplish a larger sound better than the small-diaphragm mics we already use? 
Ryan Connelly, DNA Hot Properties
Reply: Large-diaphragm mics tend to have deeper bass and lower noise than small-diaphragm mics, while small mics tend to have tighter polar patterns and less off-axis coloration than large mics. Since feedback is your main concern, small mics are the better choice. You can always equalize small mics to get more bass (if that doesn’t cause feedback).
These are the main techniques for preventing feedback:
·       Use mics with a mostly flat frequency response and a cardioid or supercardioid polar pattern.
·       Place mics as close as possible to the choir – maybe 1 foot in front of the front row, and 1 foot above the head height of the back row, aiming at the back rows.
·       Use as few mics as you can get away with. The more mics you use at the same distance from the source, the more feedback.
·       Do not use monitor speakers near the choir, or at least do not put the choir mic signals through their monitors – just the piano.
·       If the choir is small enough, try a regular stand-mounted mic close to each singer. This is a typical technique for praise-band singers of up to 12 people.
·       Aim the null point of each mic’s polar pattern at the nearest house speaker.
·       Place the house speakers as close to the audience as is practical so you can turn down the speakers.
·       Use more-directional house speakers.
·       Use a graphic EQ.
Good luck – let me know how things are working out for you.