Scott's PA System Tutorial: Running Sound

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Testing the System



The Single Amplifier Component System

This system consists of the same components as the powered mixer system discussed in the previous section. The main difference is that these components are separated into individual units rather than being combined into one single unit. These separate units include; an equalizer, an amplifier, a mixer (soundboard), speakers, and microphones. Separate effects units can also be added, but they are not essential to getting the system working. Using effects is also a fairly large subject. It is large enough in fact to get it's own section later in the tutorial. For testing purposes, we can simply keep the effects knobs (send and return) turned all the way down. They can be tested and adjusted later.

Since the single amp component system is so similar to the powered mixer system, testing it is essentially the same. Simply follow the steps outlined below.

Mono

1) After setting the knobs on the board in the same configuration as described for the powered mixer (or like the picture to the right), the first thing to do is turn the volume knobs on the external amplifier (In some amps, they are on the front. In some, they are on the back) all the way up. This will ensure that you are getting all the power out of the amp that it is designed to deliver.
2) Now, make sure the equalizer is not in "bypass" mode. There is usually a switch on the front labeled "bypass" or something similar. Make sure this switch is in the "off" position. If "bypass" is turned on, the unit will route the signal it receives straight though it without running it through the electronics associated with the frequency adjusting sliders. In other words, the equalizer will be "bypassed", and any adjustments made to the EQ will have no effect on the sound of the PA system. That isn't good, so make sure it isn't bypassed.
3) Turn the "Gain" sliders on the equalizer up to about 3/4 from the bottom. This slider adjusts the input level of the signal as it enters the EQ. Leaving it adjusted at 3/4 gets the level high enough to work with while leaving a little headroom to turn it up later if it becomes necessary. If it is left all the way down, no signal will leave the unit and travel to the amplifier. As a result, no sound will come out of the speakers. In a sense, the gain on the EQ acts like another volume adjustment. Just remember that any extreme (too low or too high) in adjustment on any volume or gain knob can result in distortion or hiss in the speakers..
4) Now, follow steps 1 through 5 as outlined for testing the powered mixer system. The only real differences at this point are in troubleshooting any problems. Since there are more connections and more components, there are simply more places to look for errors. Tracking problems down may take a little more time.
5) One more test that I like to do is make sure the EQ is working. To do this, I adjust the sliders so that the high frequencies are turned all the way down. I then check a mic. Then I hit the "bypass" on the EQ and check it again. If the equalizer is working correctly with the system, there should be a noticeable change in the sound when it is set in "bypass" mode.

Typical mixer channel controls

Since, in a non multi-amped component PA system, the configuration of the components leading to the monitor speakers is exactly the same as the configuration of the components leading to the main speakers (see Setting it up: Small Practical PA), it stands to reason that the testing procedures would also be the same. After testing the mains, follow the directions below to test the monitors.

1) Turn the main master level all the way down.
2) Follow steps 1 through 5 above, but apply it to the monitor system rather than the main. In other words, if it says "main", think "monitor".

Stereo

Running a system in stereo is nothing more than running two separate but identical signal paths out to two different sets of main speakers. To test them, all you need to do is run the same tests outlined in the steps above separately for each main output channel. Okay. If that didn't make sense, just follow the steps below.

1) Make sure all the individual "pan" knobs are set straight up at 12 o'clock.
2) If it has one, turn the master pan knob all the way to one side (Left or A, whatever the case may be). That will divert all the signal to only one of the main output channels. Basically, one side will be turned up while the other is turned down. Again, just like a car stereo. That means that during these tests, you should only expect one set of your speakers to be working at a time, depending on which way you have the pan adjusted.
3) If it doesn't have a master "pan" knob, it will have two different main master sliders, one for right (or B), and one for left (or A). Turn the left one (or A) up about 3/4 of the way, and leave the other one down. This accomplishes the same thing the "pan" knob did in step 2.
4) Now, follow steps 1 through 5 as outlined above for the mono system.
5) If it has one, turn the master "pan" knob the all the way to the right (or B). This should turn the left speakers down and the right speaker(s) up.
6) If it doesn't have a "pan" knob, turn the left slider (or A) all the way down, and the right slider 3/4 of the way up. This will pan the signal to the right speaker(s).
7) Again, follow steps 1 through 5 as outlined above for the mono system.
8) Around now, it's probably time to turn around and yell at your drummer for making all that blasted noise when you are trying to listen to the speakers. It won't do much good, but it will make you feel a little better. You will get to yell at the guitar player later, but he probably isn't there yet.
9) Turn the other channel back up to 3/4 or turn the master pan knob back up to 12 o'clock, whichever the case may be. Check to make sure that both sides of the stereo system are working by listening to both the speakers on the left side of the stage and the right side.
10) At this point, it would be really cool if you could take a little break, but chances are you're running late and don't have time, so take a deep breath or two, complain a little about how no one helps out like they should, and skip ahead to the section called "Input Signal Adjustment and EQing".


The Multi-amped Component PA System


Although this system can seem very large and complex, for the most part testing it is the same as for the single amp component system. The only additional components necessary to make this system work are lots of extra amplifiers and speakers, and a crossover (or crossovers if you are running a stereo system).

Before running the tests for these components it is important to understand the function of a crossover and to adjust it properly.

Warning:
Failure to properly adjust the crossover can easily result in damage to your system, particularly the horns and the speakers. I recommend looking up the specifications for your specific models of horns and speakers to get the proper settings.


As defined in the "Words to Know" section of this tutorial, an electronic crossover is "a rack mountable unit used to separate frequencies leaving the soundboard into highs, mids, and lows with different outputs for each." The amount of each frequency (highs, mids, and lows) going to each amplifier and ultimately to each speaker is determined by adjustments you make with the knobs on the front of the crossover unit. These adjustments are called crossover points, which basically means the points at which no lower frequencies will be allowed to pass. Think of it as a low frequency filter. For example: Say you set the highs crossover point at 1000Hz. That means that only the frequencies higher than 1000Hz will be sent out of the high "output" on the crossover. In a sense, it filters all frequencies below 1000Hz from that particular output channel.

As the warning says, getting the settings wrong can be damaging to the speakers. This is particularly true of the high range horns and speakers since they aren't designed to be able to handle any low range frequencies. It is best (and safest) to consult your manufacturer's specs to find the right crossover points, but if none are available the following settings should be safe for most (stress is on most) systems.

Bi-amp crossover points:
  • Highs - 1000Hz

 Tri-amp crossover points:
  • Highs - 1000Hz to 2000Hz (2000Hz is a bit risky without the specs)
  • Mids - 400Hz to 500Hz

These settings should be adjusted before you even turn the unit on. This will help avoid the possibility of accidentally sending a blast of low frequency signals to the high end horns.

To fully test the multi-amped PA system, follow the steps listed below.

1) Adjust all the knobs on the mixer to the same levels described and pictured for the powered mixer and the single amp component system.
2) If the crossover is equipped with knobs to adjust the volume(not the crossover points) of the outgoing signals (highs, lows, and mids), turn them each up to about halfway. This will leave you room to adjust them either up or down if it becomes necessary later.
3) Adjust the equalizer as described in steps 2 and 3 in the single amp component system test procedure.
4) Adjust the crossover points for the different frequencies in the manner described above, and turn the entire system on as described in "Turning it On" earlier in this section.

Here is where it gets a little different than testing the single amp system.

5) Turn the volume knobs on only the amp intended for the high speakers up all the way unless you are using an exceptionally powerful amp in which case you should turn them only part way up. This is because high frequencies speakers don't require as much power as the other speakers and may even be damaged if provided with too much wattage. Don't turn the other amps up yet. Since the high range speakers are the most delicate part of the system, we want to make sure that they are working correctly before we do anything else.
6) Gradually turn the main (Volume or Level) knob or slider up to near its normal setting. On knobs, straight up at twelve o'clock is good. On Sliders, three quarters of the way up is good. These settings will vary depending on the soundboard, and the personal preferences of the soundman. Just make sure you don't turn it all the way up, or all the way down. Somewhere between one quarter and three quarters is fine.
7) Turn the gain (or trim) knob on the lead vocalist's microphone channel up to about the nine or ten o'clock position.
8) While repeating the word "check" into the lead vocalist's microphone, gradually turn up the "level" knob or slider for that input channel until you can hear your voice coming out of the high speakers. You want to keep the volume low for now. The purpose of testing this way it to make sure no low frequencies are getting into the high speakers, and at very low volumes, they can handle the lower frequencies.
9) Now have someone else check the mic (or you can do it yourself if the cord is long enough) while you go out to the high speakers and listen to them to see if each is working. Make sure to place your head in front of each individual speaker. Also check to make sure no sound is coming from any of the other speakers. If there is sound coming out of the low or mid speakers, or if there is any problem in the way the high speakers sound (they should sound very high pitched, and should not be breaking up or distorting), then something is connected wrong, and you will need to retrace your connections.
10) Very gradually turn the same slider up while listening carefully for any unusual sounds coming from the high end speakers. If you hear anything wrong, like distortion or clipping, turn it back down immediately and check your connections, and gain and level settings.
11) Once the volume has reached the approximate level at which you will be running the system, and everything is still sounding a-okay, you can turn the slider level on the board and the volume on the high amplifier back down to zero and perform the same series of tests over again for the mids.
12) Once the mids check out, you can turn all the amps up to the appropriate levels (all the way for each of them with the possible exception of the highs), and proceed through the entire test sequence outlined for the single amp component system.
13) Jump up in the air, click your heels together, and shout "YeeeeeHaaaa!!!!!" or "WooooHooo!!!" or "@%$^~#*%$!!!" (Depending on where you're from) because you are finally done with testing. Now it's time to get to the actual "running" part of running sound.



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