North Ridge Community Church – Main Array Wiring Issues

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Last post I showed you some of the photographs of the room.  Now I wanted to show you the detail shots that I took of the wiring on the back of the speakers.  I would have gone up on a lift to document this but it is way too much of a hassle to remove the stairs to get the lift in the right position.

An audio tech, long before I was at the church, rewired the system at the speakers incorrectly.  Currently the high frequency/mid frequency drivers on the 4 main cluster speakers and 2 side fills are on the same amplifier channel with no delays on the system at all.  The low frequency drivers on the down fills of the main cluster are connected but the rest of the low frequency drivers of the other speakers are not connected.  Front fills are on the same amp with no delay and the two subwoofers are powered off of one amp.

Here are some of the photos of the wiring:

Here is a shot of the back of the system processor, quite good cable organizational skills eh?

This is the balanced wiring on the back of the amplifier for the front fills. Notice the awesome looking splice? This amplifier should be fed with two feeds delayed on their own.

Center Cluster

Center Cluster

Wires feeding the side fills routed from the Center Cluster.

Side Fill, Stage Left Speaker

Center Cluster, Down Fills

Center Cluster, Stage Left, Upper Speaker. Notice the wingnut wiring connectors and the speaker cables coming out of the back of the speaker?

The positive thing I have found with all of this is that their are 12 poorly labeled cables of 2 conductor speaker cable going to the main cluster from the amp room.  This means that when I rewire the system to correctly set it up I can run the four KF650e’s as tri-amped speakers and the two KF300e’s as a bi-amped speaker.  Being that it is a mono system and they are symmetrically hung in the room I can run the side fills off the same delay and eq setting.  Also I will treat the upper KF650e’s as one pair for delay and EQ and the lower pair of KF300e’s as a pair with same delay and eq.

Next thing on my list is tracing out the 12 cables in the amp room as they are not labeled!


North Ridge Community Church Sound System – Pre-Renovation

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The audio system at North Ridge Community Church in the Worship Center.

At North Ridge Community Church I was moved into the lead sound tech position a few months back.  It was my job to document the system and make an inventory of all the equipment, along with that make sure all of it was in correct functioning order.  Over these last months I have found more than I could have imagined wrong with the system.  I have a laundry list of items setup wrong, not connected correctly, NOT CONNECTED down to things being broken.

Tim Corder,, has a great audio blog online and if you get a chance you should really read it, he has some great information on there.  One thing that he stresses and I completely agree with is trust nothing that was previously installed before you.  Basically, this is saying that if one is the lead sound tech, it is his/her responsibility to make sure all of the system is in working condition and correctly setup, so take nothing for granted.

I will start out with a few of the major things I have found wrong with NRCC’s audio system:

  1. 3 of our 9 amplifiers in the amp room do not produce sound out of any speakers.
  2. Speakers in the main array have wires coming out the back of the speakers which are not connected to anything.
  3. I have found splices in the wires made with wing nut electrical connectors up at the main array. (this is probably the reason behind the 3 amplifiers not hooked up to any speakers)
  4. System Equalizer setup improperly causing “Phase distortion” which makes the sound system less defined and lacks clarity.
  5. Speakers are under powered, giving the speakers 1/3 of the power the speakers need. This is causing the amplifiers to distort much before our speakers will. By under powering speakers, the speakers are not able to reproduce the sound as well as a correctly powered speaker.
  6. Necessary delay times for the speakers are not present in our system. The 6 flown speakers are at different distances from the congregation which would require separate amplifier channels and delay times. However, all of those 6 speakers are powered off of one amplifier. Our front fills (the four speakers on the stage) have this same dilemma being powered from one amplifier.
  7. CD recorder was fed with incorrect polarity signals which caused cancellations of frequencies. This made it so anyone listening to those CD’s would have to turn up their stereos to full to be able to hear it even though it was recorded with full levels on our CD recorder.
  8. Our current system processor that handles the distribution of audio from the sound board to the separate amplifiers requires a PC with Windows 95, 98, ME or 2000 installed on it to even log into the processor to change settings.
  9. Audio Grounds not isolated at system processor and monitor amplifiers causing ground loop issues (hum).
  10. The negative wire of a balanced signal output from the board for the main array send was pulled out at the system processor leaving only the positive and shield connected causing lots of hum and noise injection.\
  11. Unity gain being sent only for the main array.  Monitors and subwoofers (sent via Post Aux send) were not receiving unity gain because of improper gain structure via the amplifiers and system processor.

So this is a good portion of what I have found so far in the system at NRCC which is wrong.  The awesome part of my job is fixing these piece by piece and discovering how much of an impact each little thing makes.

Onto my next subject, our speaker system.

Here is a photograph with the labels of each of the speakers in the NRCC audio system.

In the main cluster in the center is: two EAW KF650e (top) and two EAW KF300e (bottom) for the down fills.  The side fills are one EAW KF650e on each side.  Front fills are using the EAW JF50s which there are four of them.  Lastly we have our EAW SB625zP dual 15″ subwoofers, one on each side of the stage.  These are powered using Crest Audio and TOA amplifiers.  System processor is two TOA DP-0206.

I have an EAW representative coming out to inspect the speakers to check functionality of the components in the boxes and verify that they are hung in the correct alignment.  As far as I can tell, they look to be correct.  The KF650e’s, which are the main array and side fills, have a vertical throw of 45° and horizontal of 60°.  The KF300e’s, which are our down fills, have a vertical throw of 45° and horizontal of 90°.

This is a panoramic of the entire room. Mix position is the same location as this was taken, just on the 2nd floor balcony.

This clearly shows the upper two EAW KF650e’s and the lower EAW KF300e’s. Those green bars are pretty ulgy eh? I am sure glad there are no lights on these things during services!

In this image you can see the side fills and main array as well as the four EAW JF50s used for front fills.

You can see the projection from the side fills in this image.

This is a great pano of the room showing the vertical angle of the side fills in the room.

Finally, a great shot of the depth of the room with the mix position on the 2nd floor balcony.

A good view of the depth of the room at NRCC.

Next post is going to show some of the wiring nightmare at the main arrays.  Like always, if you have any questions feel free to ask.  Thanks for reading.

Monitors – Board Unity Gain vs Amplifier Output Gain

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Today’s post is regarding monitors.  At North Ridge Community Church, NRCC, we run our three separate monitor mixes from the front of house.  These monitor mixes are fed via the pre-fader aux sends, go through a graphic equalizer, amplified by a Crest Audio amplifier and then show up to our JBL floor wedges.

This is a very normal way to do monitor mixes and all is great, until… I discover how it is truly set up.

  • The amplifiers in the amp room are all turned up to full.
  • The output of the board aux sends are not full signal.  In fact they don’t have enough signal to light up the -21dB light on my equalizer.
  • 100-105dB volume normally output by monitors.
  • AC hum present when system is turned on.

Because the are turned up so loud, the aux send knobs are in the 9 o’clock to 11 o’clock range.  While this doesn’t sound that bad, on the Allen & Heath ML4000 the unity gain (+0dB) for aux sends is at 3 o’clock and the knobs are a logarithmic potentiometer.  They act just as a normal fader does on the sound board, where there is more resolution in the higher areas of the fader.  Basically if you move the aux send knob from 9 o’clock to 10 o’clock you would increase the volume by 10dB.  If you were to move the knob from the 2 o’clock to the 3 o’clock position you would increase the volume by 1-2dB.

Found at is a perfect graphic for explaining the logarithmic taper of the potentiometers that are used in aux sends.

Another thing that is happening by having such a low output from the board and the amps turned up high is easily explained in the graphic below that I made:

By having the board turned down and the amplifer turned up to full, you have made your signal to noise ratio very small. But when changed to a full board output and to a lower gain on the output of the amplifier you will have a high signal to noise ratio giving you less noise in the monitor system and better clarity.

As shown in the above graphic, by having the board aux output turned down and the amplifer turned up to full, you have made your signal to noise ratio very small. By keeping it this way you amplify the noise along with the small signal sent from the board.  This makes for a noisy system. But when changed to a full board output and a lower gain on the output of the amplifier you will have a high signal to noise ratio giving you less noise in the monitor system and better clarity.

By keeping your board output in a unity gain region you have higher resolution on the aux knob giving you an easier time mixing the monitors.  Also this leads to when you do an AFL (after fader listen solo) you don’t need to turn your headphones up to hear it.

After turning the amplifiers down and turning the board up I was able to keep the same overall volume with the monitors but now there is no audible noise in the room from the system being on.  If you find yourself having a hard time getting a consistent monitor mix or a noisy system, you might want to double check your amplifiers output gains to make sure they are receiving a unity gain signal.

Polarity issues in CD recording from bad wiring

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Balanced audio signals are a great thing for the audio industry. If you don’t know much about balanced vs. unbalanced signals, I highly suggest doing some reading on Wikipedia.

Balanced signals have a differential amplifier on the output and the input side. They basically carry a mono signal down 3 conductors. Two wires carry the signal and then the last wire carries the ground. The beauty of the differential amplifier is that two wires that carry the signal. One wire carries the normal signal, then the other inverts the polarity. So, the two signals are out of polarity of each other. At the receiving end of the balanced signal, there is another differential amplifier which inverts one of the wires and sums them together to get the signal back to normal.

If there is any noise injected into the wire on its run, it is injected into both wires in polarity. When the signal reaches the receiving end of the wire, that differential amplifier inverts the polarity of one of the wires which cancels out the noise. This is because the noise is now out of polarity with each other and, in the summing process, cancels out itself.

Illustration from showing how noise is rejected in a balanced signal.

At North Ridge Community Church, NRCC, we have a Tascam CD recorder which we use to record the spoken word of our services. I noticed one day that I had to turn up the CD really loud in my car to be able to hear it. This surprised me because earlier in the day I was almost clipping the meters with the CD recording levels. I decided to rip the CD into Cubase 5 to see what was going on. Here is what I found:

Out of Polarity signals which were recorded to the CD like this.

As you can see, the left and right channels are recorded out of polarity to each other. Basically, they are cancelling each other out from the inversion.

After seeing this on the screen, I went back to the church to find that the CD recording feed is coming from a balanced mono send off of a matrix on the Allen & Heath ML4000. The cable then goes into a 1/4 inch stereo to R and L RCA adapter. The way this adapter works is for a headphone cable which takes the left from the tip and sleeve and the right from the ring and sleeve. With a balanced signal, the tip and ring are inverted in polarity. So this is sending the + into the left while sending the – into the right.

I recorded a video of myself explaining what is going on when you have a signal that is out of polarity. In the video, I accidentally mention that this could be called 180 degs out of phase which is incorrect. The only term to call this is out of polarity.

After making the correct type of adapter with the balanced to RCA, the recordings will now have full volume on the CD recording with a full spectrum sound. This is another reason not to trust any installed wires without checking them.

Drew Brashler