Rane AC 22S Operation Manual - Page 14

Setting the Output Level Controls Choosing the crossover frequencies was the easy part. Now it gets real fun. The idea is to set the output LEVEL controls on the crossover so that the entire speaker system has a uniform, flat response. Unfortunately, the room in which the speakers are placed has a habit of always getting into the act, so things get messy. As a result there seems to be two schools of thought regarding the use of active crossovers. The Set‑lt‑Once‑And-Glue‑lt School. The philosophy here is to use the crossover to flatten system response as much as possible without room acoustics involved. This means setting up the system outside (unless you happen to have a very large anechoic chamber handy) and with the aid of a realtime analyzer and pink noise source, adjust all of the crossover outputs so the system is as flat as possible. Once the system is tuned, the crossover is then locked behind a security cover (posted guard is optional) and never again touched. It is then the job of the system equalizer(s) to normalize or flatten the system to each different room. The Fix‑lt‑With-The‑Crossover School. Here the crossover knobs get a good workout, for the crossover is used at each location to help flatten the system along with the equalizer. Some even maintain that a good active crossover can work alone like a parametric equalizer in the hands of an expert. This does require experience, skill, and the right equipment to back it up (not to mention a licensed set of ears). Regardless of which school you profess, the absolute importance and effectiveness of some kind of realtime analyzer in your system cannot be overstressed! No, this is not a callous plug for our other products; analyzers in general have come a long way. They're out of the lab (i.e. closet) and into the hands of every smart working musician and sound technician. An analyzer will save tremendous amounts of time and provide the absolute consistency, accuracy, and plain old good sound that very few ears on this earth can deliver. They are affordable, easy to use and amazingly effective. You owe it to yourself and your audience to at least look into one of these analyzers - you'll wonder how you managed at all without one. Whether by analyzer or by ear, here are a few recommended methods of setting the crossover Output Levels. Setting Levels With a Realtime Analyzer NOTE: If you are running two Channels, tune up only one Channel at a time. 1. Set all LEVEL controls to minimum; leave Delay and crossover Frequency controls as set previously. 2. Place the analyzer microphone at least 15 feet away from the speaker stack, on axis (dead ahead) and about chest level. Minimize any background noise (fans, air conditioners, traffic, etc.) that could affect the readings. 3. Run pink noise through the system, either through a mixer channel or directly into the crossover. Turn all amplifier controls at least half way up. 4. We will use the 3‑Way mode here as an example-the procedure applies to all configurations. Turn up the MASTER LEVEL control about half way. 5. Slowly turn up the LOW LEVEL control until you hear a healthy level of noise through the low frequency drivers (it should sound like rumble). 6. Adjust the analyzer display control so it shows the greatest number of 0 dB indicators below the crossover frequency. 7. Now slowly turn up the MID LEVEL control until the display shows the same output level average as the low frequency section. 8. Repeat this procedure for all crossover frequency sections, so the end result is an analyzer display that is flat as possible. IMPORTANT: Compression driver or horn roll‑off, bass roll‑off, and room acoustic usually cannot be corrected by the crossover. If you are using constant directivity horns, see the Constant Directivity Horn Modification section on page 12. If, for example, you are adjusting the HIGH FREQUENCY control and observe a decline in frequency response somewhat above the crossover point, then set the HIGH LEVEL control for equal display level near the crossover point and leave it there. Then use an equalizer or bank of tweeters to correct the roll‑off problem. If you are tuning the system in a room, the acoustics will greatly influence the system response, as shown by the analyzer. Check the system response on an analyzer at several other locations and adjust the crossover as necessary to reach a fixed compromise setting if desired. If you plan to use the analyzer only once to set the crossover, set up the speaker system in a quiet place outside or in a very large concert theater, and run pink noise at low levels with closer microphone placement to keep the room acoustics out of the picture as much as possible. Manual-11