Feedback ControllersFeedback Killers ensure that feedback is avoided. These so-called "Feedback Destroyer", "Feedback Eliminator" or "Feedback Controller" devices really work. Feedback killers have extremely steep and narrow filters that detect the disturbing frequencies and are active throughout the concert and extinguish the feedback whistle before it occurs. It sounds like an ingenious solution and it is! Purists may suggest that these filters are also audible and therefore disturbing. We have tested this equipment and while these filters are clearly visible the human ear seems to be insensitive. Used sensibly the Feedback Killers from Sabine and DBX are really not audible, according to some customers however cheaper feedback suppressor have their weaknesses in exactly this area, this fact is also mentioned in numerous forums. The cheaper devices can be made good use of when you run them exclusively into the monitoring system, so that the front signal remains unprocessed. These feedback killers are run between the mixer and amplifier, or even placed on the subgroups with the microphones, since other signals like electric guitar, keyboards etc are not at all affected by the feedback. Feedback can be avoided differently: 1. The complete system and also the monitor just quieter. 2. In empty, echoing rooms with reflecting walls you can alter the room acoustics with carpets, curtains, sound-absorbing materials such as SAS-mats. 3. The microphones as close as possible to the sound source, so close to the mouth or the guitar as possible. The speakers as far away as possible from the microphones, as close as possible to the concert audience 4. Loudspeakers with high directivity use (column, line arrays) 5. Use the right microphones. Cardioid and Hypercardoid, mics like the popular Shure SM58. 6. Provide strong signals by powerfully singing into the microphone and do not move out in front of the speakers. 7. Unused, open mic channels on the mixer should be turned off, these open mic channels provide feedback and also undefined mushy sound. 8. Using in ear monitoring as apposed to the traditional stage monitoring . 9. Acoustic guitar, the pick up on the monitor system, the microphone for the room. 10. Filter out interfering resonance using an equalizer, but that is not easy and definitely an intervention on the sound which may also prove positive. The conclusion is that in professional concerts there is no feedback, the problem is manageable. Good Feedback Killers work and are a convenient.