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. [. . . ] Adaptive Parametric: The FBX Solution The Sabine FBX Feedback Exterminator® is the next step in the evolution of feedback control. The FBX is essentially a self-tuning parametric EQ. 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 out performs other EQs five ways: 1. 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. It typically finds and eliminates feedback in less than one second. 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. What about that 6 to 9 dB increase in gain?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. We would need an enormous system to drive six feedback points. In this system, damping six feedback points could easily deliver well over 15 dB net gain!How much gain do you achieve with the six FBX filters?Six resonance points worth - whatever that happens to be in your unique system. [. . . ] The definition of constant Q is blurring. Many equalizer manufacturers claim their equalizers have constant Q filters, when in fact they get substantially wider as they get deeper. The only way to know for sure if the filters are truly constant Q is to inspect their frequency response curves. 7 & 8. ) Net Gain Before Feedback Many people measure their increase in gain by the amount they push up the mixer's calibrated slider. [. . . ]