March 14, 2017
Have you ever struggled with stage monitor feedback that you couldn't control? Or maybe you found that you couldn't get enough volume and clarity out of your system without causing feedback? If so, you might want to master the lost art of 'ringing out' your stage monitor system. What does it mean to 'ring out' your monitors and how will it help you overcome feedback issues? I'm glad you asked! In this series we'll examine the world of live sound on stage and see how this essential technique can yield huge gains (no pun intended) in terms of quality sound on stage.
What is feedback and why is it following me?
Most musicians have a general idea about feedback, because it is a very common live sound issue. We are all familiar with the runaway feedback from howling acoustic guitars or microphones squealing, but the details are a little less understood. Feedback happens when a signal loop forms between the speaker and the microphone, bursting into oscillation at the most prominent frequency present. When this happens the oscillation reinforces the offending frequency causing a 'runaway train' effect. The mic is picking up the signal exiting the speaker and sending it back through the system which causes the runaway frequency to emphasize itself. It usually isn't long before you're drawing dirty looks from the club manager and your fans in the audience. And while those dirty looks can put you under a lot of pressure, it is important to know that the system is giving you a clue about how to solve the problem. Find the offending frequency and lower it in the channel or the mix. This breaks the signal loop, and stops the feedback. It sounds easy enough, yet we've all suffered in a situation where the sound tech didn't understand this concept well enough to get the feedback under control.
Stack the Deck in Your Favor
There are some important considerations to keep in mind when working to banish feedback. Ringing out the monitors is crucial, but you first need to get the situation setup as best you can. If the setup is really poor, then ringing out the monitors may remove too many frequencies and you have to raise the volume, putting you right back where you started.
Sound waves are directional and they reflect off of surfaces in the room. This can be especially challenging on tight club stages with musicians playing at extremely high volumes. In these cramped quarters, the sound waves can bounce off the walls, ceilings, and even the musicians crowded together, sending the monitor signal right back into the mics. To begin with, it helps to keep the stage volume to a minimum practical level. You also want to be careful with mic and monitor placement. A mic pointing straight into a monitor will amplify the signal exiting that monitor thus producing feedback. Pay attention to your placement and try to eliminate this problem by orienting your microphones for maximum rejection in the direction of the monitors. Stage mics typically have the most rejection at the rear when using cardioid pattern microphones, like Carvin Audio’s M68, and slightly off-axis to either side plus the rear for hyper-cardioid pattern microphones. So it really helps to face the mic in essentially the same direction the speaker faces with the back of the mic turned towards the speaker. This takes advantage of the microphone's built-in rejection of off-axis sounds.
Carvin Audio's M68 Microphone has a cardioid polar pattern for excellent off-axis performance and feedback control.
While reducing your stage volume is critical to avoid pushing the limits of audio physics too far, it is equally important to make sure that you get a strong signal out of each of the instruments or voices you want in the PA. In general you want to keep your mic as close to the source as possible. This reduces the need for excessive gain at the mixer, and it reduces stray signals from adding to the gain of possible feedback. As in many things, balance is the key. If you have control of the environment, try adding soft surfaces in the stage area. This helps diffuse the sound waves reducing reflections. It also helps if you can keep signal sources separated as much as possible, so the mics pick up the instrument you want without amplifying other sources. Amplifying other sources through several mics increases the group gain of that source and its potential for feedback. This is often the hardest thing to ring out, because it is in all the sources. And finally, be careful adjusting the input gain on your mixer. If the source requires excessive gain then go back and check the source, mic placement, and its potential to reflect or directly enter your monitors.
Many times these basic ideas are enough to achieve a good monitor sound without feedback. But for those times where you need more help, you'll want to master the art of 'ringing out' the stage monitors. In part two of this series we'll discuss this technique and give you the tools to combat feedback in more challenging venues.
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