User manual SABINE POSITIVE FEEDBACK BROCHURE

[. . . ] The Advantages of FBX Feedback Exterminators® Positive Feedback INSIDE: Story of Feedback Equalization The FBX Solution Glossary of Tech Terms 1 2 3 5-8 Version 3 TM ® The Story of Feedback By Doran Oster, President Ever since Lee DeForest invented the first vacuum tube, engineers have walked the tightrope between feedback and system gain. The purpose of this guide is to give you the tools to get all the gain you need without the agony of feedback. We'll start with a common-sense discussion of the techniques sound engineers now use to control feedback to get the most gain and clarity out of their sound systems. Our imaginary work bench Imagine a mic and speakers set up in a tiny shower room. [. . . ] In the early days of sound reinforcement, these filters were custom made to a specific frequency and width for a specific application. Now there are a number of commercially available parametric filter sets that allow engineers to dial in the width, center frequency and depth of the filter. The problem with parametrics is that they're expensive, they require a good deal of expertise and auxiliary equipment to tune properly, they require constant retuning whenever the room acoustics change, and they are far too slow and cumbersome for catching feedback that occurs during the program. Adaptive Parametric: The FBX Solution The Sabine FBX Feedback Exterminator® is the next step in the evolution of feedback control. It constantly monitors the program, searching for tones that have the overtone signature of feedback. Once feedback occurs, the FBX automatically places a very narrow, constant-width filter directly on the feedback frequency and lowers it just deep enough to eliminate the ringing sound. The FBX finds and eliminates feedback automatically before and during the program. The FBX's narrow filters eliminate feedback without losing the fidelity of the sound. Fig. 2: Graphic EQ Typical Graphic EQ: -10 dB cut at 500, 630, 1K, 1. 25K, 1. 6K & 2K Hz If the graphic EQ really had 1/3-octave filter widths, the frequency response curve would vary 6 dB between sliders. This would ruin the sound. Graphic EQ's usually use one octave wide overlapping filters that provide much smoother frequency response curves. Notice that the overlapping filters add together to cut -16 dB when the sliders are only pulled -10 dB. 3. Use wide-filter graphic EQs for controlling the shape of the sound and narrow FBX filters for controlling feedback, and you'll typically achieve a 6 3 THE FBX SOLUTION to 9 dB increase in gain compared with using the EQ alone. Gain increase from equalization really depends on the characteristics of the sound system and the room. Returning to our imaginary system in the shower room, the sound bounces off the hard tile surfaces and reflects back into the microphone with only a slight touch of the volume slider. If you filter the first feedback point, you can only increase the volume fader a touch more before the second feedback occurs at a new frequency. Even if you filter six different resonance points, you may only achieve 1 or 2 decibels of net gain because there are so many low-energy resonant paths. When we set our system in a large open field and the speakers are far away from the microphone, we really have to crank it up before we hear the first feedback. In this system, damping six feedback points could easily deliver well over 15 dB net gain!Six resonance points worth - whatever that happens to be in your unique system. You can maximize your gain by following our anti-feedback directives and by learning more about how the FBX filters work best for your situation. Microphone Mobility Mobile karaoke and wireless microphones present a special feedback challenge. It does little good to set a number of filters for a mounted microphone if you plan to carry the mic around the stage to differ- ent locations. [. . . ] The frequency response curve shows that the biggest cut in power, called the center frequency is at 1, 000 Hz, that the filter removes half of the power (-3dB) between 645 Hz and 1550 Hz, the Q of the filter is 1550-645 Hz/1000 Hz (. 905), and the maximum depth is -12 dB. 6 shows the frequency response of two adjacent sliders pulled down 12 dB. The combined filter width is 1. 49 octave and the two filters add together to give a maximum depth of -19. 3 dB. Constant-Q Filters Frequency Response Curves A frequency response curve is a graph that shows the gain of a component or a group of components at different frequencies. 6: Typical Frequency Response Two overlapping EQ sliders pulled down 12 dB It is common to describe a filter's quality factor, or "Q, " as the center frequency of the filter divided by the filter width (in Hertz) measured at the -3dB point. [. . . ]