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6.2 Feedback Control A graphic equalizer can be used to provide some control over moderate feedback problems, but does not have enough flexibility or resolution to handle severe situations. You will achieve the best results when you can eliminate one or two feedback points by setting one or two sliders for no more than a 6dB cut. Often you can find a feedback point by boosting sliders in succession to determine which frequency ranges contain the feedback modes, and then cutting those ranges. Be very careful in this process to avoid explosive feedback and possible system and hearing damage! If you find feedback points with many equalizer bands, remember that cutting every band may not help (all you will do is reduce system gain). The combination of a graphic equalizer for tone control and a parametric equalizer (such as the Ashly PQX-571 or PQX-572) for feedback control is highly recommended. 6.3 Console Channel Equalization Many mixing consoles provide only simple equalization for individual channels. If your console has channel inserts, you can patch your graphic equalizer into a channel that’s being used for something important (like your lead singer) and use it to tailor the sound of this channel exactly the way you want. 6.4 Large Room Equalization Large rooms tend to suffer from multiple reflections with long time delays, long reverberation times, and “ring-modes”, all of which lead to reduced intelligibility and a generally “muddy” sound. As sound travels long distances through the air, high frequencies are attenuated more than low frequencies. In general, large rooms benefit from some low frequency roll-off, high frequency boost, and attenuation of ring mode frequencies. As in the case of feedback control, a graphic equalizer can help reduce an isolated ring-mode or two, but a tunable narrow-band equalizer such as a parametric is more effective here. Operating Manual - GQX 3102, GQX 3101, and GQX 1502 Graphic Equalizer 7. DESIGN THEORY While most graphic equalizers look very much the same, there are several important differences in the circuitry used to implement various designs. Perhaps the major differences are in the filters. Some equalizers use a filter made of a capacitor, an inductor, and a resistor, or “RLC” filter. The advantage here is simplicity, but the real disadvantage is the inductor itself. An inductor is a coil of wire with a core of some sort. Inductors are susceptible to hum fields and they are large and expensive. Other equalizers use the same basic approach, but replace the inductor with a “simulated inductor”, which is actually a circuit comprised of an amplifier, a capacitor, and a couple of resistors. This adds parts but is less expensive than a real inductor. The problem with this approach is that simulation is less than ideal; it produces an inductor with high resistive loss resulting in poor curve shape when used in a filter. Another problem with all these “RLC” designs is that large capacitors must be used for the lower frequency filters, limiting the choice to large, expensive non-polar types or electrolytic capacitors with poor audio performance. Also, when this filter type is combined with a potentiometer to adjust the equalization, the resistance of this pot affects the “Q” of the filter so that a little equalization produces a much broader curve than a lot of equalization. The other filter approach is a true bandpass filter. This can be made with no inductors and more practical sized capacitors; the “Q” is easily set and remains constant, and the parts count is reasonable. there are several types of bandpass filters suitable for this job. Ashly uses a “Q” enhanced Wein-bridge filter. Because it is a “symmetrical” design using matched tuning components, the “Q” is easily set and is very stable. VAR Z C L R Figure 7.1: Passive RLC Filter Design VAR Z - + Figure 7.2: Simulated Inductor Filter Design - + OUT IN Figure 7.3: Wein-Bridge Filter Design Operating Manual - GQX 3102, GQX 3101, and GQX 1502 Graphic Equalizer In designing a graphic equalizer, a selection of filter sharpness must be made. More sharpness (higher Q) produces less filter overlap and tighter control over an individual band, but also causes “ripple” in the frequency response when many filters are boost or cut together to produce a flat response. We feel that the graphic equalizer’s primary use is for “voicing” and tone control, and have set our filter sharpness to produce a maximum of 1dB ripple. The summing system in a graphic equalizer is also important. Since there are a number of filters which combine to produce the overall response, it is important that the filters not interact (they WILL overlap, but the response of one filter should not modify the response of another). Ashly uses an “interleaved” summing system where every other filter uses the same summing amplifier so that adjacent filters never share the same drive and feedback signals. This allows the filters to maintain their natural response...
Questo manuale è adatto anche per i modelli :Strumenti Musicali - GQX-3101 (142.44 kb)
Strumenti Musicali - GQX-3102 (142.44 kb)