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Setting it up: Part 3


Crossovers

       Up until now, we have dealt with PA systems that use a single amplifier to power a set of full range speaker cabinets. In addition to speakers and horns, these cabinets are equipped with internal passive crossovers. Basically, crossovers are little electrical devices that receive a fullrange signal and divide it into separate outputs of midrange frequencies, lowrange frequencies, and highrange frequencies. That way, the highs are sent only to the speakers designed for the highs, the lows are sent only to the speakers designed for the lows, and the mids are sent only to the speakers designed for the mids. Passive crossovers do this by dividing the signal after it leaves the power amp while active crossovers do this by dividing the signal before it gets to the power amps.

       Passive crossovers (located inside full range speaker cabinets) are good in that they make it possible to provide a full range of sound using only one amplifier, but they are a little inefficient. Since all the speakers are working from the same source, the low speakers, which require more power, will tend to rob power from the higher frequency speakers and horns.

       Active crossovers (plugged in-line before the amplifiers) are good in that they make it possible to power the mids, lows, and highs from different amplifiers. This way you can use a big super-duper amplifier for your lows, and use a smaller amp for the mids and highs. This is a much more efficient use of power, and it gives you the ability to acquire a much more powerful and full sound. The catch is that using an active crossover requires a lot more equipment and expense.

       Using an active crossover in a system is sometimes called bi-amping or tri-amping. Below is an example of tri-amping the mains in a mono system.


Example 4: Tri-Amping the Mains


[Tri-Amp System]


       With the exception of the signal path to the main speakers, example 4 is exactly the same as example 3. The effects loop and the monitor system should be connected in the same way as before, but now the mains have been turned into a tri-amped system. To do this, a crossover, three separate amplifiers, and three separate sets of speaker cabinets must be used. Each of these amplifiers as well as each set of speaker cabinets must be designated to a specific audio frequency. Which frequency goes where is determined by the outputs on the crossover. The "low out" should go to the input of the amp with the highest wattage because the low end speakers will require the most power, and the "high out" should go to the amp with the lowest wattage because the horns will need the least power. Just remember that it takes a lot more energy to vibrate the great big cone on a fifteen or eighteen inch speaker than it does to move the tiny diaphragm in a midrange horn.

Warning:
Never plug a high end speaker or horn into the amp that is plugged into the "low out" of the crossover. These speakers are not designed to handle such low frequencies and will be damaged very quickly if hooked up incorrectly.


To hook up the system in example 4, follow steps 1 through 15:

Monitors and Effects

  1. Connect these together as described in example 3.

Mains (Keep in mind that even though the signal flow splits inside the crossover, it still flows from the mic toward the speakers)

  1. Plug a high impedance cord into the main "output" of the mixer.
  2. Plug the other end of this cord into the "input" of the main equalizer.
  3. Plug another high Z cord into the "output" of the equalizer.
  4. Plug the other end of this cord into the "input" of the crossover.

Lows

  1. Plug a high Z cord into the "low output"of the crossover.
  2. Plug the other end of this cord into the "input" of the highest powered amp.
  3. Plug a speaker cord from each "speaker out" of this amp into the "input" of each low speaker (one cord to each speaker).

Mids

  1. Plug a high Z cord into the "mid output"of the crossover.
  2. Plug the other end of this cord into the "input" of the middle powered amplifier.
  3. Plug a speaker cord from each "speaker out" of this amp into the "input" of each midrange speaker (one cord to each speaker).

Highs

  1. Plug a high Z cord into the "high output"of the crossover.
  2. Plug the other end of this cord into the "input" of the least powerful amplifier.
  3. Plug a speaker cord from each "speaker out" of this amp into the "input" of each Midrange/high horn (one cord to each horn).
  4. Take a break. That was a lot of work.



       To see how a large super-duper stereo PA system with multiple effects loops, monitors, and compressors is hooked up, simply click on "next page". Be patient though. The diagram is a little bit on the large side and will take a little time to load up.


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Introduction · System Setup · The Powered Mixer (combo) · Stereo to Mono · The Small Practical PA · Effects (loops) · Monitors · Multiple Effects · Crossovers · Tri-amp Systems · Diagram (Large PA) · Multiple Effects Loops (revisited) · Compressors · The Snake · Running Sound · Turning It On · Testing(Powered Mixer System) · Testing(Single-amp System) · Testing(Multi-amp System) · Signal Adjustment (Input/Output levels) · Equalizing(EQ)/Feedback Control · Words to Know · Tips and Tricks · Message Board · Home Recording

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