Behringer SHARK FBQ100 Manual - Page 8

8 SHARK FBQ100 User Manual If you are using not just one FBQ100 for the monitor path, you should employ Monitoring P.A. some additional units to safeguard critical signal paths. Experience has shown that during a concert the musicians on stage usually want their instruments made louder in the monitors. With the SHARK you can raise the volume without running the risk of feedback. When the concert begins the FBQ100 automatically tracks and removes varying feedback signals produced by "moving" vocal microphones. 2.2 The feedback destroyer in the SHARK +4 dBu Line Monitor Out Master Out Fig. 2.4: Two SHARKs in the monitor path The SHARK identifies feedback by splitting the entire frequency spectrum (20 Hz to 20 kHz) into sections of 1/60 of an octave and determining the level of each of these bands. The values calculated are then referenced to the level of the overall signal. The resulting level difference determines whether or not a filter is set. The SHARK allows you to adapt these decisive parameter to your needs: within a range from 1 through 100 you can edit the feedback detection sensitivity. The standard setting is 50, which ensures the best possible detection of feedback for the majority of applications. For speech-only applications you can raise the feedback detection threshold towards 100, which enables the algorithm to detect and remove feedback even more quickly. Vice versa, lower values provide for a more stable feedback suppression responding less to wanted feedback-like signal portions produced by guitars or keyboards. 2.1.5 The SHARK used in single channels and subgroups Whenever you want to make sure that wanted feedback such as the feedback sounds produced by a guitar won't be removed, you should insert one or several FBQ100 into "feedback-prone" single channels (e.g. vocals) or subgroups of your mixing console! Route all channels that are susceptible to feedback (e.g. all vocal mics) to one or several subgroups, in which you insert one or several SHARKs. In this way, all channels that are less liable to produce feedback (e.g. those carrying line-level signals, or instrumental microphones with lower volumes) can pass the console unaltered, while only critical microphone channels are controlled by the FBQ100. Thus, you can protect your sound reinforcement system against feedback and still use wanted feedback sounds. Send Return Mixer Insert Point Return +4 Line Out dBu In Send Ground Ground In FILTER LEARN mode, feedback is generated and suppressed automatically. Whenever it detects feedback, the FBQ100 selects the filter parameters automatically to efficiently remove the feedback. As the filter is set to the frequency detected, this mode is ideally suitable for suppressing constant feedback frequencies produced by "fixed" microphones, e.g. those used on drums. Once set, the filters automatically enters lock mode, i.e. the frequency remains fixed but width and depth of the filter are still being adapted to the signal. The filter width is enlarged whenever the feedback frequency shifts slightly. If feedback persists, gain is reduced even more and kept low to prevent feedback from recurring. All microphones that are moved during a performance (e.g. hand-held vocal microphones) are usually susceptible to varying feedback frequencies, which should be suppressed in automatic search mode (entered when you power up the SHARK). Much like in FILTER LEARN mode, a filter automatically determines the ideal settings for all parameters, in order to suppress feedback. However, once all filters have been set, the filter first activated gets reset to automatic search mode. Thus, the SHARK makes sure that there is always one free filter to identify and remove new feedback frequencies. If your music contains wanted feedback elements (e.g. guitar feedback), the SHARK will suppress these too, because it is impossible from a physical point of view to distinguish wanted from unwanted feedback. Section 2.1.6 provides some information on how to get around this physical problem. 2.3 The integrated delay Fig. 2.5: The SHARK in the insert path 2.1.6 Automatic "tuning in" of P.A. and monitor systems With the FBQ100 you can improve the protection against feedback even before a concert begins, simply by "tuning in" your sound reinforcement system: once the system has been installed and set up, open all microphone channels and monitor paths, then enable FILTER LEARN mode on your FBQ100. The SHARK generates short feedback-causing signals, which are then sent back to its input and suppressed by the filters. These filters are permanently assigned and can be reconfigured as free searching filters only by means of a RESET. Without the SHARK you could raise the overall volume level only until the first feedback occurs. But with the FBQ100 you've got considerably more headroom! Please note that the FILTER LEARN mode is limited to about 15 seconds. In addition to speakers on or near the stage, major-scale installations often have speaker groups positioned at a distance to the stage or flown above the audience, in order to provide listeners away from the stage with direct sound. However, since sound needs some time to travel around (343.6 m/sec at 20°C, accelerates by 0.6 m/sec per °C), it reaches the audience not simultaneously but gets delayed by a certain amount. To make up for the different run times between stage and remote speakers, the latter must be provided with an electronically delayed signal, which is usually done by means of special-purpose Delay devices. You won't need them, however, when you've got a SHARK, as the FBQ100 integrates a Delay Line circuit giving you the same convenience of operation as dedicated devices. Simply measure the distance between the various speaker groups and enter this value (in meters or feet). Chapter 2.1.3 shows you how to wire the FBQ100 in this type of application.