Why Feedback Often Starts Before the Mixer
Feedback is often treated as a console problem. The sound-guy hears the ring, grabs an EQ, pulls down a frequency, and hopes the system behaves. Of course, some sound guys know the deal, but many just lack experience.
The quick EQ technique could work in a pinch but , oft-times, is not the real answer. In fact, you could find that the problem is the room!
Feedback begins with a physical loop. A microphone picks up a source. The sound system amplifies that source. Some of that amplified sound returns to the microphone. If enough of it comes back at the right level and frequency, the system “rings” or takes off.
The mixer did not create that loop by itself. The room, the loudspeakers, the microphones, the stage layout, and the gain structure all helped to create it.
That is why placement matters so much.
In AVL’s video “You Can’t Fix Bad Sound With EQ” Seth explains how his early live-sound experience taught him to get results with very limited tools. There were no digital consoles, no gates, no compressors, and very limited EQ. Good results depended on placing microphones and loudspeakers correctly, because there was not much technology available to rescue a bad setup. Today we have modern tools to help but, as he explains, ‘physics is forever!’
Physics Is Forever!
If a loudspeaker is aimed at reflective surfaces, the room sends energy back where it is not wanted. If microphones are placed too far from the intended source, they pick up more room sound and less direct sound. If stage volume is excessive, open microphones capture more spill. When monitors are aimed poorly, they can feed directly into vocal microphones. What a mish-mosh mess!
And, each of these conditions reduce gain before feedback.
EQ can diminish the severity of certain feedback frequencies but, obviously, it cannot change where the loudspeaker is aimed. It cannot move a microphone closer to the source, and it will never be able to make a reflective room less reflective. It cannot stop loudspeaker energy from exciting a wall, ceiling, or corner, either.
EQ is a useful tool after the system has been physically set in its proper place to succeed. It is not much of a rescue plan when the layout itself is causing the problem.
Understanding this is especially important in churches, schools, auditoriums, and multipurpose rooms where volunteer operators are often asked to solve complex acoustic problems from behind a console. If the system layout is wrong, the operator may be blamed for feedback that was accidentally designed into the room.
That is unfair to the operator and expensive for the owner.
A better approach starts earlier:
- Evaluate loudspeaker coverage.
- Look at microphone locations.
- Consider stage volume.
- Listen from multiple seats.
- Measure the room when needed.
- Identify where sound is going before deciding how to process it.
The goal is not to avoid EQ. The goal is to stop asking EQ to solve problems that belong to design, placement, and acoustics.