Guide to Avoiding Microphone Feedback

Guide to Avoiding Microphone Feedback

What Is Feedback?

Feedback occurs when a microphone picks up sound from a speaker and re-amplifies it in a loop, producing a loud squeal or hum. It’s most common in live sound setups.

1. Microphone Placement Best Practices

  • Keep microphones behind speakers, not in front of them.
  • Point the back or side of directional mics (like cardioids) toward the speakers to reject sound.
  • Maintain a consistent distance from the mic—closer is better for signal strength and less gain.

2. Use the Right Microphone Type

  • Cardioid or supercardioid mics are best for feedback control—they reject off-axis sound.
  • Avoid omnidirectional mics unless necessary (e.g., in theater with lavaliers).

3. Control Stage Volume

  • Turn stage monitors down and avoid aiming them directly at the mic capsule.
  • Use in-ear monitors instead of floor wedges whenever possible.
  • Keep instrument amps from blasting into open mics.

4. Use EQ Effectively

Ring Out the System (Manual EQ Notch Cuts):

  • Slowly raise mic gain until you hear the beginning of feedback.
  • Identify the feedback frequency and cut it using:
    • A graphic EQ: Lower the suspect frequency band.
    • A parametric EQ: Narrow the Q and make a deep cut at the problem frequency.

General EQ Tips:

  • Roll off low end (high-pass filter) on vocal mics to reduce rumble.
  • Avoid excessive boosting in the 2 kHz–8 kHz range, where feedback often occurs.

5. Use Gain Structure Properly

  • Set mic gain (trim) properly—strong enough to get a good signal, but not so high that it causes feedback.
  • Use compressors sparingly, as too much gain makeup can increase feedback risk.

6. Use Feedback Suppression Tools

  • Many mixers (like Behringer X32 or digital stageboxes) include feedback suppressors or auto-EQ.
  • Standalone devices like dbx AFS2 or digital processors can automatically notch out problem frequencies.

7. Minimize Open Mics

  • Mute unused mics.
  • Use gating or automixers to reduce the number of open channels.
  • Avoid using multiple mics for a single sound source (especially podiums or choirs).

8. Train Performers & Presenters

  • Instruct them to speak directly into the mic.
  • Avoid “wandering” off-axis or pointing the mic toward a speaker.
  • Don’t cup the microphone head—it changes the pickup pattern and raises feedback risk.

9. Test and Soundcheck

  • Always do a soundcheck to identify feedback-prone mics or positions.
  • Walk the stage with the mic and listen for trouble spots.
  • Set EQ and gain levels before the audience arrives.

10. Have a Plan B

  • Keep mute buttons or a kill switch handy in case feedback happens live.
  • Know how to quickly lower master faders or cut suspect channels if needed.