Stage monitor squeals and rings are just part of dealing with the live sound part of the business. But if you know the theory, and the tricks to suppress the evils of stage monitors, then you are halfway there. In this article, we will go down the list of things to make your gig a more squeal free performance.
When I came up against the demons of rings and squeals, I threw money at the problem, and sure enough it helped a lot. But good microphones, stage monitors, and fancy signal processing does not have to be the only cure for rings and squeals. But as I oft pontificate, good microphones are your first priority when money is made available to improve the sound system. And a microphone noted for its tight pickup pattern is especially prized for acoustic feedback rejection. The down side is that singers with poor mic technique will struggle at first on tight microphone patterns (i.e. hyper-cardiod mics).
When it comes to stage monitors, flat frequency response is what you want. This is because any peak response frequencies in the speakers or mics will be the first to ring when the monitor level is turned up. Now add a performer with a brimmed hat, and things get tougher as that fashion accessory becomes a nice presence band reflector to guide even more wedge mix into the vocal mic. Good stage monitors are the second money priority in budget, so cheap is as cheap does. Back to that “flat” thing. Do not make the mistake of falling for the music store demo with a CD and buy the one that sounds really great. It is likely being “goosed” with some kind of EQ either through the board or internally in the case of powered monitors. Ask for a spec sheet and look at the frequency response which should be as flat as possible through the bulk of the speaker’s range.
When it comes to mics, we have cardioid and hypercardiod mic pickup patterns, and each have feedback notches unique to the pattern type. Cardioid mic patterns on the cheaper mics, like the famous Shure SM58, have their rejection point directly in the rear boresight of the mic. Tighter pattern mics with super or hyper-cardioid pickup patterns, have multiple rejection points but slightly off the rear of the mic (where the cable plugs in).
With cardioid mics, the mic should be tilted up at the vocalist with the rear pointed at the wedge. When using mics with super/hyper-cardioid patterns, the wedge or wedges should be slightly offset to be in the rejection notches for maximum feedback rejection. Also tight pattern mics should be more level in the mic clip to put the rear (which on a tight mic actually picks up more sound than it does from about 15° off center) into the audience and not near the stage monitors.?
Ringing Out With Equalization
The whole process of ringing out the stage monitors is to counter the un-flatness of the contributing electrical signal processing and speaker and mic transducers. That is why most monitor mixes employ electronic frequency equalizers between the monitor mix auxiliary output of the mixer and the monitor amp rack. Parametric or Graphic Equalizers are commonly used for ringing out, with most sound persons using a graphic equalizer due to the visual feedback of the frequency response via the fader positions. Ringing out the monitors works best with a few prerequisites. One is that your line checks are complete and all mics are up and close to their performance gain settings. The next is that performers have their preferred mixes and they are roughly dialed-in. Then drop all aux masters driving mixes to very low levels and taking one mix at a time. Then slowly crank up the mix via the aux master until a ring begins to appear.
As a ring begins to sensed, a notch-down on the suspect frequency fader by 3 to 6dB should be done, and then resume bringing the aux master level up to get to the next ring. This all works well if you have experienced ears and know your third-octave frequencies in your head.
When about two to four ring tones are suppressed, that is about when you should stop the process on that mix and call it good enough. Another clue that you are getting to the end on ringing-out are that very little aux master increases cause another ring to occur, or multiple rings at the same time. One other clue that something terribly is amiss on mic/monitor placement, or a suspect bad mic, is that one ring frequency keeps coming up after killing it repeatedly.
No one said that you have to do ring outs at the last minute onstage before the gig. If you bring your own sound system, ring it out at rehearsals first to shorten up or eliminate the ring out at the gig. Most rings and squeals are due to mics and monitors paired together, and not the stage acoustics.
Of course, other more obvious methods are out there to identify ring frequencies. Peavey’s FLS (feedback locating system) is a patented display of LEDs next to equalizer faders that permits rapid ring identification and cues the operator for a fader notch maneuver. Similarly, Real-Time Analyzers (RTAs) can be attached to mics or signal lines to display rings or potential rings as they occur. Today we are also beginning to get feedback suppressor signal processing to aid in automatic ring/squeal squashing. Even without such technology, with training you can pick out the ring frequency with your ears for the trouble-making third-octave band long before it has a shot of blooming into a full blown squeal.
One thing to be aware of, is that many automatic feedback suppressor products have entered the market with mixed results. While most get the job done, most do take some time to detect a ring, and let a ring persist for part of a second before a filter placed on the offending ring. The nasty thing about these automatic suppressors is that the detection algorithms are not ever good enough to determine a feedback ring from a loud guitar note held for a long time. So for some sustained note performers, beware that the suppressors may engage if the instrument is in the mixes.
Originally posted 2009-08-22 18:43:28.