Problems with feedback can make a great, well-rehearsed band sound, well, maybe a ‘challenging listen’ would be a diplomatic way of putting it. However you describe it, “a shower of angry kittens” for example, getting rid of feedback – or stopping it occurring in the first place – is one of the easiest ways to get your performance sounding more professional.
I’d still practise though…
How to stop feedback happening
Obviously, as with so many things, prevention is better than cure; so let’s start there. Unwanted feedback is almost always caused by the vocal mics picking up too much of the PA or monitors.
Knowing this, positioning of the microphones and the PA and monitors is critical. Knowing the polar pattern of the mic is of key importance here. Most vocal mics – including the Shure SM58, will be cardioid, with the maximum amount of rejection directly to the rear of the mic.
However, other vocal mics, such as the Shure Beta 58a, are supercardioid (hyper cardioid mics have the same problem), and so have a pickup ‘lobe’ directly behind the mic. So, when positioning your foldback monitors, they’ll want to be directly behind the mic for cardioid, and firing into that dead-spot at 45 degrees behind for the supers and hypers.
If you’re holding the microphone, keep your hands away from the grille! If you cup your hands around the interesting end of the microphone, you change a lot of aspects of the mic’s performance, which will also make you sound less good, so convince your singer not to do that!
At certain smaller gigs, you might not have separate foldback and you could be relying on the PA to hear what you’re playing. This can complicate your setup, and some compromises will probably have to be made between what you hear, where you stand, what the crowd hears, and how loud you can play.
Once you’ve got a setup that works, scribble a wee sketch and take some measurements and you can use this as a basis for the next performance. Things might change a bit depending on the room, but it should give you somewhere to start.
Getting rid of feedback when it happens
For a lot of gigs, you’re not going to have the opportunity to get there in advance, soundcheck thoroughly, ‘ring out‘ the room/PA combination and deal with potential feedback frequencies by notching out regions with a graphic eq.
You may also be engineering your own gig, so if feedback happens during a song there’s not going to be anyone there to deal with it! If you can, arrange the setup so you can reach the mixer from your performance position. While it’s not ideal to have to adjust a fader part-way through a song, it’s probably better than letting a lupine howl tear throw the eardrums of your adoring audience!
The dbx AFS2 the rescue!
When you’re getting on with the gig and flying without an engineer, having a box that can solve your feedback problem for you can be a great for your peace of mind, letting you get on with what you should be doing: performing.
The dbx AFS2 feedback suppressor is one such box, and could prove to be a valuable addition to your live rig…
The dbx AFS2 is a 1U rack-mountable unit that you connect between your mixer and your amplifier or powered speakers. Alternatively, if your mixer has them, you can patch it into the master insert point using XLR or TRS connections.
The job of the dbx AFS2 is to listen for those troublesome frequencies popping out and feeding back, and notching them out as you would do manually with a graphic EQ. Unlike a regular 1/3rd Octave graphic though, the filters on the AFS2 are very, very, very narrow, meaning it chops out less of the sound you want to hear, while still working hard to stop feedback ringing through.
Not only does the quick and easy ‘Wizard’ button let you get set up and lock those filters to the problem frequencies as part of your soundcheck, the filters can also be used in ‘live’ mode, constantly scanning for feedback and dealing with troublesome frequencies on demand; perfect for unattended live use and hopefully keeping your hands away from the mixer when they should be producing sweet sounds elsewhere!
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