Behind The Mixer

Learn Church Audio Artistry | Church Sound

Topics:

Photo provided by BeverlyLR

Your worship leader has been knocked to the floor as his floor wedge suddenly explodes with a huge volume increase.  The church service ends and you’ve got thirty minutes until the next service to find the problem and fix it.  Where do you start?

A very similar scenario happened to a friend of mine working in the pro audio field.  Only it happened for four nights in a row until the problem was solved.  And the primary reason it took so long to fix was that someone above him didn’t recognize the ways equipment can fail and thus denied my friend’s request for a swap of a particular piece of gear.

Equipment usually fails in a couple of ways;

  • Volume drop
  • No volume / no signal
  • Signal cuts in and out
  • Decrease in sound quality

These failures are usually simple things like a short in a cable, a bad cable, or a blown piece of equipment like a power supply or internal electronics.  There are also problems like a blown speaker.

What about the boost in the monitor volume?

No, my friend didn’t crank the gain or any such thing.

Let’s look at the signal path;

  • Sounds come into the mixer from mic’s, instruments, and a computer.
  • Mixer possibly routes signal to effects units.
  • Mixer sends signal out to an amp.
  • Amp sends signal to monitor.

Using this path, let’s look at the possible sources of a problem;

  • Cables
  • Input sources
  • Digital Mixer
  • Amp
  • Monitor

Right off the bat, we can drop cables from out list of potential problem sources.  Also, as all the input sources are boosted in the monitors, we can drop those off the list.  It’s something after the signal gets to the mixer.

Now we are down to;

  • Mixer
  • Amp
  • Monitor

Monitors fail down.  Blown power supply, blown speaker cone, blown fuse.  Our list is getting shorter.

Where would you put your money between the amp and the mixer?

You’re going to say the amp…not because you think that’s going to be the source of the problem…but because you really don’t want the problem to be in the mixer.  You’d have to get it serviced.  Repair could be expensive.  You’d have to borrow another mixer.   “Denial ain’t the name of a river.”

Truth be told, the amp is going to fail down as well.

Hate to break it to you…your mixer is busted.

My friend knew this and wanted to swap mixers but the “higher up” continually denied that possibility and so forced him to try everything from cable replacement to monitor replacement until finally recognizing it was the mixer.

Summary

Stuff fails.  You are alerted to this failure by what you hear (or what you don’t hear).  Knowing how equipment fails will help you diagnose the problem correctly and get the system back up and running as soon as possible.

Question: What failures have you encountered?

Reader Interactions

Thought? Questions? Comments?

Notify me of followup comments via e-mail. You can also subscribe without commenting.

Comments

  1. Before going to IEM at my church, we had a very similar instance of a floor wedge suddenly exploding in volume during a service. My instance it was the guitarist’s wedge and he turned his guitar down to compensate at the time. Since his guitar was the loudest piece in his mix that got us through the service. After service I got up to the stage and had him play while I troubleshot the issue. In this case it actually WAS the cable, or specifically the jack on the end of the cable going into the wedge. It was bent very slightly and a little wiggle and it would either make full contact or only some. Our stage vibrates when the subs are hitting hard and what we later figured out is that that vibration could wriggle that connection enough to mess with the contact it was making. Between services I just connected his wedge to a different aux from the mixer that had a good end on it and copied his mix to that aux.

    Reply

  2. I think I’m missing something here. According to your article,
    “Equipment usually fails in a couple of ways;
    ■Volume drop
    ■No volume / no signal
    ■Signal cuts in and out
    ■Decrease in sound quality”
    Yes, my experience agrees with that. Extremely rarely does equipment failure cause an audio signal to get louder. If it is not an intermittent, it usually results in added distortion or a drop in gain, or both.
    In your example the volume suddenly got significantly louder. How did it fail upwards in just that monitor mix? Or were there other things going on also? And the story isn’t clear as to the timeline. Your telling makes it sound like it happened four times in a row at the end of the service. So is it time related? Meaning, heat related?
    It’s not clear how the console in this example failed upwards. It may actually be an intermittent in the board that wasn’t recognized by the operator. Compensating with gain for a signal that is down 6 dB or more due to an intermittent contact (related to electronic or mechanical failure) can be disastrous when the intermittent makes full contact once again, usually after it heats up enough to fully bridge the break.
    Your friend actually did his troubleshooting the right way. The console is the least likely suspect in a problem like this. Mics are usually out of the picture – they just distort and drop gain in failure, almost never intermittent. Cables are the first thing to check, and the most likely to fail, especially related to balanced lines. That can cause a signal to drop in level and change frequency response.
    Drivers can’t fail up, but amplifiers might. Amps can seem to fail upwards, but it’s heat related. They don’t really fail upwards, they just are down in gain (due to intermittents) until heat causes connections and/or circuits to work properly, and then they operate normally again. It’s rare these days, but it can happen.
    Swapping out the mixer is difficult and time consuming. One should always look to eliminate the simpler parts first when troubleshooting. If your friend did his diligent troubleshooting, narrowed it down to the board and was then denied the ability to swap it out, that is a failure of management and budget.
    Troubleshooting is a skill that gets more precise with experience. Seeing failure over and over again helps you zero in on what it might be, and what it probably isn’t. But the most important rule of trouble shooting is:

    ** Never change more than than one component at a time! ** (cable, box, processor, device)

    If you change two or more things, and you solve the problem, you will never know which of them was the problem. And you can still never be sure what the problem was, unless you can make it happen again – i.e. duplicate the problem at will by putting the suspect component back in place.
    Thanks for pointing out the importance of proper troubleshooting. It is a skill as important as any to the modern sound engineer.

    Reply

    • It’s been a while since I wrote that article but I wrote it after I heard my friend’s full story. In short, like you said, “If your friend did his diligent troubleshooting, narrowed it down to the board and was then denied the ability to swap it out, that is a failure of management and budget.” And that’s exactly what it was. Except, in his case, it wasn’t a church but a professional venue. It was a problem within the console send that was driving that particular wedge / side fill. Everything fails sooner or later. Some times, it’s in the least likely of places.

      Reply

  3. I had 2 problems with one of the first-generation Crest Audio HP-8 consoles. The first was that a couple of the subgroups would cut out intermittently. An Internet search and a call to the Crest tech support folks got me a set of new ribbon cables once we determined that contact cleaner wouldn’t fix the original cables.
    The second problem was that the Mono output only output highly distorted audio for very loud signals (signals that were to loud for comfort, but that reproduced cleanly on the Left and Right outputs), but was silent for anything below that magic level. Another call with Crest tech support had a new PCB for the mono section in the mail.

    The experience has taught me that having extra capacity is very important – when the 2 subgroups went out, I had 2 unused subgroups that I could switch to. It’s also important to understand all the equipment in a sound system – I needed to know how to re-assign subgroups (and how a fader-flip switch changes the controls on those unused subgroups), as well as how to use the loop out on the amplifiers to get around the loss of a main output. And I promise I don’t get paid to say this: it’s really nice to have good tech support, and the Crest tech support guys were great about helping me work around these issues, and promptly mailed me the replacement parts. The only thing they didn’t do a great job at was instructions on how to take it apart – since it was my first time taking any console apart, it took longer than it should have, and I wasn’t sure what I was doing for the first half.

    Reply

  4. My issue I am still having. We’ve been using a AT wireless lavier for pastor for years. It has been solid.

    Recently we got a headset mike for it, and in general its OK, but when the pastor gets loud for emphasis
    you can hear a bit of distortion on the peaks. “Overdriving something in body pack says I” and I crank down the pot in the body pack. That didn’t work.. Plan B? Which I don’t really have yet. I suspect the first stage of amp from the mike which I guess is before the pot (signal wise).
    This last Sunday we had a guest speaker and I restored the original mike and as usual it was solid. This is one of those things 90% of the congreation doesn’t hear, but I can hear it!

    Reply