Question: Recently I was setting up an auditorium for classes and encountered some problems. We needed to connect multiple microphones (four in total) for lecturing, interpretation, and Q&A sessions. After reviewing some documentation on mixers and microphones, I came up with the following questions...

Question:

Subject: Questions about recording

I ran into your site when looking for solutions for setting up our auditorium for classes. We need multiple microphones (four) for lecturing, interpretation, and questions. After checking out some documents of mixers and microphones, I have the following questions:

  1. Do dynamic microphones or condenser microphones better suit our need?
  2. What's the difference between a balanced and an unbalanced microphone? A mix manual says it only supports a balanced microphone via an XLR port. Why?
  3. How does one avoid the high frequency screaming noises when using a microphone?

Many thanks.

Answer:

The consideration for speech and music is different. Fortunately you can save some of your budget. Here's my suggestion:

  1. Dynamic microphones are cheaper and sturdier, thus recommended. However, I suggest getting those with cardioid, supercardioid, or even hypercardioid polar patterns to minimize feedback problems.

  2. Modern microphones with XLR ports are usually balanced. One of the XLR line is to balance the zero volt ground line, thus minimize ground loop humming. If you are running very short cables, it's possible to connect an unbalanced microphone via an adapter; if you are running slightly longer length, a balanced microphone will greatly improve the signal quality; if you are running long cables, a preamp is highly suggested to level your signal to line standard.

    In addition, if some of the microphones are to be passed among the audience, wireless microphones may be a good direction to go. You can get a multi-band or multi-frequency receiver. In sum, you might save more this way than having to dig your floors when cabling.

    Also, please take some caution in phantom power switches and line layout. Condenser microphones need the phantom power to operate but not dynamic ones. If you use unbalanced microphones, be sure to check the line layout and the switch status.

  3. These are common ways to minimize the feedback problem:

    • Avoid pointing the microphones to the speakers;
    • Use microphones that support cardioid, supercardioid, or hypercardioid polar patterns;
    • Use a device called feedback destroyer (or something alike); it detects the problematic frequency and automatically EQs it out.

    In the studio setting, we simply use a pair of headphones to avoid leakage; in a live setting, changing the direction of the speakers or the signal paths usually helps; feedback destroyer is usually my last choice when other means fail (mostly it leaves my music signal intact but not always).

Tsan-Kuang