How to Remove Audio Feedback through Equalization

By Chris Huff

Not all feedback is eliminated in the same way. Feedback typically occurs when a microphone and a loudspeaker are too close together thanks to a singer dropping the mic to their side. In this case, let's call it user error. But have you ever had multiple people use the same microphone and suddenly you hear the ringing of feedback? Have you ever created feedback by altering the EQ of a channel? Let's find out why.

What is feedback?

Audio feedback is the sound created when a sound loops between an audio input and an audio output. A simple example is a microphone and a monitor. The monitor is broadcasting sound the microphone then picks up. The monitor then is amplifying that sound and broadcasting it back out where the microphone picks it up again. Eventually, when the volume going into the microphone is the same as the volume coming out of the monitor, feedback begins.

The first frequency that feeds back is the one that requires the least amount of energy to excite resonance. Resonance is a vibration of large amplitude caused by a relatively small stimulus of the same or nearly the same period as the natural vibration period of the system.

What are the common reasons for audio feedback?

  1. Microphone located too close to a monitor
  2. Gain structure set too high so as frequencies primed for feedback


What can be done to stop audio feedback in these cases?

  • Move the microphone
  • Move the monitor
  • Use a more directional microphone to meet your mic'ing need.
  • Turn down the monitor volume
  • Turn down microphone gain (likely the person needs to hold the mic to their lips if singing)
  • Watch for reflective surfaces that might be bouncing the monitor sound to a microphone not directly in line with the monitor. Then, make changes then using one of the above.
  • Simple but common...turn off microphones when not in use. A stage arrangement can change for an event and create the right conditions for an open mic to cause feedback.
  • Equalize the microphone channel signal, lowering the frequencies which are causing the feedback.


How does the equalization-for-feedback process work?

In the first part of the article, I mentioned the frequency that required the least amount of energy to excite resonance. Let's lasso that one to the ground!

Frequencies by their sound:

  • Hoots and howls: Likely caused by a feedback frequency in the 250 to 500 Hz range.
  • Singing: The range is in-line with 1kHz.
  • Whistles and screeches: most likely above 2 kHz.


Determine the likely frequency range and then apply a cut to that range by 3dB.

What about creating feedback when EQ'ing a channel?

It's that very EQ process where we can cause feedback ourselves. For example, one time I had choir mic's all set and EQ'ed to my liking. During a specific song, I decided to try boosting the mid-range EQ a bit more (that 1kHz range). That's when the feedback started. I quickly cut that mid-range frequency back before anyone (except my sound guy, Jeff) noticed.

The keys to feedback control

Eliminate the conditions in which it can appear. Teach singers to hold the mic right up to their lips...and never drop down next to a monitor, establish proper gain structure, and turn off unused mic's.

When it does appear, know that you have an immediate alternative to turning down volumes...you might just be able to EQ it out.

Question(s): What have you done to control feedback in your environment?


By Chris Huff, of www.behindthemixer.com. Used by permission.


Free Book: A Tale of Two Mixers

There has been a whole lot of hubbub about several new, smaller digital mixers.

Sorry. All gone, now.
A very short book has been written comparing features on the most popular among them: to sort through the hubbub, and examine them in light of the real world. Part tongue-in-cheek, part real-world review, part spec comparison, it's a useful tool. And hey, it's FREE!








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David McLain, CTS | Technical Sales CCI  SOLUTIONS
Be seen. Be heard.
PO Box 481 / 1247 85th Ave SE
Olympia, WA  98507-0481
Voice: 800/426-8664 x2155 / Fax: 360/754-1566
personal email: dmclain@ccisolutions.com
CCI Solutions online: www.ccisolutions.com
Church Soundguy blog: www.churchsoundguy.com

Fitting a Countryman E6 Mic

The Countryman E6 and E6i mics are among the most popular mics in the world today. But fitting them is a little tricky. Here's how it works best.

When Old Becomes New: Hearing Loop Assisted Listening Systems

As more of our nation is diagnosed with hearing loss, it's important that we offer our parishioners the best assisted listening options possible.
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It’s always interesting to see old technology become new again.

We see it daily in our lives, but I’m referring to a specific type of old tech; hearing loops.

The technology, which is correctly known by the name of inductive loops, has been in existence for decades.

Based on Faraday’s law of induction, a magnetic field is created and individuals that have a Telecoil (t-coil) equipped hearing aid, can receive audio signals directly in their hearing aid.

A “loop” is a relatively low-tech solution. In simple terms an area is surrounded “looped” with a piece of copper wire.

An amplifier drives signal down that wire creating a magnetic field inside the “loop”.

To receive the magnetic signal a person inside of the field simply has to switch their hearing aid to the “T” (t-coil) position.

With the current ADA (American Disabilities Act) requirements and an aging population, providing a loop based hearing assistance system can be beneficial not only for compliance but also for the convenience of our parishioners.

“Hearing loss is a significant issue. As the baby boomers come of age, the years of industrial sounds and/or noise pollution coupled with exposure to loud music has accelerated the problem,” says Todd Billin of Hearing Loop Systems.

With 36 million of Americans reporting hearing loss and over 8 million already outfitted with hearing aids, the need for hearing loops continues to grow.

There has been no stronger advocate than David G. Myers, PhD, Professor and Social Psychologist at Hope College.

When visiting Europe and attending a service at an old cathedral, Dr. Myers noticed a sign on the wall and remembered the words of the audiologist he purchased the hearing aids.

He knows upon seeing the “Hearing Loop Installed” sign that if he flipped a switch on his hearing aid he’d be tapping directly into the house audio.

Sure enough, from the moment Dr. Myers flipped that switch he has been and continues to be a huge supporter of the technology.

He is the creator of hearingloop.org, a website that provides education and information on hearing loops.

“I activate my T-Coils and instantly the speaker’s voice comes to me not from some distant loudspeaker but seemingly from the center of my head, says Myers.

“My hearing aids now serve me as customized wireless loudspeakers”

There can, of course, be challenges when installing a loop system.

The most obvious being how to route the cable in an existing space.

“In all of the existing buildings in which I have designed and installed loops, including very old churches, airport terminals and sporting venues, like the Michigan State Breslin Center, I have always found somewhere to hide the wire for the loop system,” says Tim Vander Meer of Hearing Loop systems.

A loop can cause a high pitched noise through some instruments pickups such as guitar, piano, strings.

Generally speaking this usually happens on older pickups or installations where there is not a solid ground present.

Spillover into adjacent rooms can also be an issue; this also can be overcome by using a properly designed phased array system.

The advantage of a loop is that there is no need for portable receivers and batteries as the t-coil in the hearing aid requires no power.

Additionally the hygiene issue goes away as earphones do not need to be cleaned and shared.

However, for those individuals not using t-coil equipped hearing aids, portable receivers are still, of course, available.

There is also a cost/benefit savings compared to traditional RF and Infrared systems, as the only limit on users of loop systems is physically how many people can fit inside of a loop.

As you consider assisted listening systems for parishioners in the future, whether for compliance or convenience, I would certainly consider a loop system.

What are your thoughts on assisted listening systems? Let me know in the comments below!

Gary Zandstra is a professional AV systems integrator with Parkway Electric and has been involved with sound at his church for more than 25 years.

From ProSoundWeb, used with permission.