dbx PX User Manual
Also see for DriveRack PX: Features & specificationsQuick start guideManual
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Contents
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A.8 System Setup and Gain StructureThe DriveRack PX offers a wide range of tools for sound system design and setup. These toolscan make your system more efficient and better sounding, but to get the best possible soundit is important to use these tools properly. In the DriveRack PX we have included a Wizardsetup tool to help in system setup. If you use the Wizard to set up your DriveRack PX it willautomatically set the limiters for some powered speaker selections. If your powered speakersare not available in the Wizard, you should choose the Custom setting. The following sectionexplains how to maximize system gain and how to use the limiters to protect your poweredspeakers from clipping.In traditional system design, the output of your mixer would be routed to a system EQ, acompressor, and a crossover with output level control. From the crossover, there may beadditional filters that are employed to improve the response of your speakers. There mayalso be limiters set up to keep your powered speakers from going into clipping and protectyour speakers from the hazards of a clipped signal. Your powered speakers play a vital role insystem setup, because they are last item in the chain and offer the greatest amount of gain(that is their job after all). If your powered speakers are incorrectly setup you will not beusing your system to its fullest potential.One thing that is critical to system setup is maximizing gain structure. Gain structure refersto aligning the gain of each device so that they all clip at the same point; and the noisefloor of the entire system is at its absolute minimum. Quite often PA systems are setup withthe amplifier input controls turned all the way up in the incorrect assumption that this isthe only way to get the maximum output level. Amplifiers are fixed gain devices, turningdown the amplifier input levels does not change the potential output of the amplifier; it onlyrequires more input voltage to get full output power. Many amplifiers will clip with an inputlevel greater than +6 dBu when the input controls are turned all the way up. Most mixingmixers can deliver over +18 dBu of output level before clipping. This means that with youramps tuned all the way up you are sacrificing 12 dB of headroom, resulting in poorer noiseperformance and the potential of system clipping. By adjusting the amplifier controls properly,you can maximize your system performance.A way to set up your system for maximum gain structure is to use the clip indicators and levelmeters of the mixer, DriveRack PX, and the powered speakers. To do this, hookup the output ofthe mixer to the input of the DriveRack PX and the outputs of the DriveRack PX into the inputsof your powered speakers. Set up the DriveRack PX for your particular powered speakers. Makesure that the output limiters are turned off on the DriveRack PX. Run a continuous signal (pinknoise or sine wave – many test CDs are available that have these types of signals) through yourmixer. Turn up the output of the mixer until it begins clipping. If there is no clip indicator onthe mixer then use the output meters; most reputable mixer manufacturers use red LEDs at thetop of the meters to show the onset of clipping. Once the mixer is clipping, back the outputgain down slightly until the clip indicator on the mixer turns off. Turn up the level control onthe powered speaker until the clip indicator begins to turn on. Turn the level control downslightly, so the clip indicator no longer is on. If the top red LED lights on the input meters onthe DriveRack PX, then you must reduce the level of the mixer feeding the DriveRack PX. If thetop red LED lights on the output meters on the DriveRack PX, then you must reduce the levelDriveRack® PX Section AAppendix® |
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