Feedback Problems in your PA System?
Running sound for a band is not the easiest thing to do and can often times cause even the best sound engineers a lot of headaches. Typically, getting your monitor mix where everyone is happy and without feedback, is the toughest challenge (in my opinion). It never fails, that you can start the show out with everybody hearing themselves, but then as the show progresses, the crowd gets more into it and the guitarist will reach back and crank his amp up just a little. Well, the bass player can’t be outdone, so he bumps his amplifier volume just a bit, etc… Now, the vocals need to be brought up in the monitor mix. Here comes the feedback!!!
Let’s go back to sound check before the show. It is extremely important that you have proper microphone placement. When possible, position the microphone where it is on axis with the floor monitor. Avoid pointing the microphone at the speakers, if this happens, you will never get a good strong monitor mix and you will be dealing with feedback throughout the show. Also keep in mind…the better vocal mic you use will help reduce feedback. A Shure SM58 can be found for around $80-$100 and it’s a really nice microphone. The placement of the floor monitor
is important as well. Sound reflects off of objects which can sometimes cause feedback through the sound reflection coming back through the vocal microphones. Keep that in mind when positioning stage monitors
A graphic equalizer is your best friend when it comes to eliminating feedback. I recommend a long throw 31 band eq. The long throw sliders make it easier for you to cut out the right frequency without cutting too much. Long throw just allows for more precise adjustments.
I always start with the eq flat. Turn up the monitor output on the mixer for the channel you are using. Turn it up until you start to get feedback. If it’s a low rumble, try pulling down 80 Hz-125 Hz. If its high pitched, I tend to find that 2k or 4k will usually help out. I generally roll off the high end of the eq from 10k and above. The vocals won’t go that high, so you shouldn’t even notice it’s not there. Once you have done it enough times, your ear will get trained to the frequencies, so it will be easy to find the proper slider. There is seldom a need to boost any frequencies. I like to get the vocals as loud as possible without feedback and then lower them down. This will allow some headroom when the vocalist says they need more monitor volume. Some people (especially at karaoke
) like to cup their hands around the microphone…almost guaranteed feedback! You definitely want to try to avoid that.
It’s really nice to have different monitor mixes for each musician. This allows much more control over the levels and much easier to please than running one universal mix.
These are just my opinions from my 10 years running sound. Hope that some might find it helpful.