Rane AC 23S Operation Manual - Page 13

Time Delay Adjustment Using Realtime Analyzer & Pink Noise This method outlines the use of a realtime analyzer, pink noise generator and flat response microphone to set crossover time delay. The procedure applies to virtually any analyzer system. We recommend using a 1/3 or 2/3-octave analyzer as either of these is more likely to match your specific crossover points than a one-octave analyzer. And it is important to match the analyzer to the crossover point as closely as possible for proper phase alignment, otherwise the analyzer readings may be misleading. STEP BY STEP PROCEDURE A 3-Way mode consisting of High, Mid and Low drivers is used here as an example. For other configurations, use the same procedure starting with the highest crossover point and repeating steps 2 through 5 for each lower crossover point. NOTE: If you are running two separate channels on the crossover, tune up only one channel at a time, using the same procedure for both. 1. Place the analyzer mic about 15 feet in front of the speaker stack and at a height about midway between the high and mid drivers. Turn all crossover LEVEL controls fully down. 2. Connect the pink noise source to the crossover INPUT (or mixer or wherever is convenient). Turn up the crossover MASTER LEVEL control and the MID OUT control until noise is heard only from the mid driver at a comfortable volume. 3. With a healthy but not uncomfortable volume of noise from the mid driver, set the analyzer level control so the display corresponding to the high crossover frequency is reading 0 dB. 4. Press in the MID MUTE switch on the crossover so the tone is removed from the mid driver. Without re-adjusting either the meter or the crossover Input or Mid Level controls, turn up the HIGH LEVEL control until the tone coming from the high driver reads 0 dB on the analyzer. 5. Now release the MID MUTE switch on the crossover so pink noise is heard from both the high and mid drivers. Switch the display sensitivity to ±3 dB (not necessary with full scale analyzers) and observe the display reading at the crossover frequency: i. If the display shows a +3 dB reading, then the drivers are properly phase aligned and no delay is necessary; leave the MID DELAY control at minimum. iii. If the MID DELAY control is all the way up and you still do not have a +3 dB (red) reading, you will have to physically move the high driver farther forward until the display shows +3 dB (red). The amount of displacement correction available from the Delay depends on the actual crossover frequency: the higher the frequency, the less amount of correction capability. If the drivers are built into a single cabinet and/or it is impossible to change relative positions, then you will have to obtain additional external delay to achieve proper phase alignment. such as the Rane AD 22B. iv. If turning the MID DELAY control up makes the display reading decrease instead of increase, this means that the high driver is actually in front of the mid driver; adding delay to the mid driver only worsens the situation. There are a couple of ways to deal with this: a. Try to move the high driver back as far as possible without losing stability in balancing the speaker stack. You may want to raise it up as well to restore dispersion close to the stack. If you cannot move the high driver, then you will have to use an additional delay source to align the high and mid drivers. The built-in delay system in the AC 23S is designed to accommodate the majority of common speaker configurations; if you encounter confusion or difficulty with your particular system, it is best to consult your dealer or the Rane factory for assistance. b. If this decrease in the display due to the DELAY control occurs at a low frequency crossover point below about 150 Hz, set the DELAY control to minimum and leave it there. Frequencies below 150 Hz are actually omnidirectional, so that phase misalignment is virtually inaudible below this point. Subwoofers will often possess long folded or straight horns, resulting in the diaphragm being well behind the rest of the stack. Most authorities agree that phase alignment of subwoofers is unnecessary. 6. Lower the microphone until it is vertically midway between the mid and low drivers. Repeat steps 2 through 5, using the crossover LEVEL control, MUTE switch and next DELAY control. You may start each series of steps 2 through 5 at a different volume as necessary-but once the Levels are set in step 3 do not alter these until step 5 is completed. Once all of the crossover DELAY controls are set, then adjust the output LEVEL controls as outlined on page Manual-13. ii. If the display shows less than +3 dB reading, slowly turn up the MID DELAY control on the crossover until the display shows +3 dB. Now the drivers are electronically phase aligned. The Delay control should be left in this position unless the speaker system is physically altered. Manual-10