Troubleshooting Audio Problems in Your P.A.

As with anything, eventually, you’re going to have something break, stop working, or just plain not “sound right” in your sound system. You will have to diagnose the problem, and find the easiest, fastest solution to the problem and get it fixed with the least amount of drama or attention being drawn to the situation.

The first step is to diagnose what the issue is in a broad sense. To do this, you’re going to need to hear it and be able to try certain things, so this part of the procedure will be behind the console. What is, and what isn’t working? Once you figure out what isn’t working, you need to figure out in what way isn’t it working? Is there just no sound? Is there sound, but it is distorted? Is there clean sound, but the level isn’t right? Etc. (It takes longer to read this paragraph than it should to perform this step.) This has to be done in a logical sequence to zero in on what piece of gear has broken in the least amount of time, and in a way that doesn’t waste effort. Start with the most likely cause, and if that isn’t it, move on to the next most likely cause. Eventually, you will find it.

Once you’ve narrowed down the result of the problem, it’s time to begin to narrow down the offending piece of equipment. You do this by swapping parts for known good parts, or connecting them to a known good piece.

Here’s an example: Let’s start with the easiest possible example – a vocal mic doesn’t work, and you are sending a monitor feed from the FOH console, so there is no splitter or monitor console. You solo that channel, and it’s dead – no sound at all. All of the other mics work and sound fine. It’s a dynamic mic, so it doesn’t need 48V phantom power, so that’s not an issue. There is no distortion in the FOH system or monitors. That narrows it down: you know that the basic system works – the speakers work, the amps are alive, the crossovers, EQ, and snake returns work. The thing that is not working is limited to one channel. The possible causes are (in order of signal flow): mic; mic cable; snake channel; console channel.

So, let’s re-arrange that to the order of likelihood of failure: mics rarely fail, and console channels don’t fail very often, and usually not total failure. That leaves the mic cable and that channel of the snake. From experience, I know that mic cables fail much more often than snake channels, so the first thing I would do is replace the mic cable with one that you KNOW is good. Then test the mic. If it works, great! If not, go to the next step. Still using the known good replacement mic cable, plug that mic cable into another channel on the snake, and test.
If it STILL doesn’t work, plug that snake channel into a different mic input on the console, and test. If it STILL doesn’t work, the only thing left in that chain is the mic.

It is this process of elimination that will help you find and fix a problem in the least amount of time, and with the least amount of effort. A problem like this isn’t a time to drag out cable testers or the like. You’d spend about as much time testing the cable in awkward locations (like beside the drummer, in the dark, with everyone waiting on you) with your tester, as it would take to swap it out.

As you might have gathered from this example, it’s easiest to fix things that don’t work at all – totally dead.

You WILL run into situations where things work fine . . . sometimes. Things will be going smoothly, and suddenly something breaks. Just as you start to troubleshoot, it starts working again! These problems can be the most difficult and frustrating problems to deal with, because you can’t find out what is broken while it is working. Sometimes it will only happen once in a great while. You can still go through the troubleshooting exercise to narrow it down to one particular group of parts.

Let’s say that all of the subwoofers cut out for a few seconds, and then just as suddenly, start working again. In your mind, you can do some troubleshooting. You know, for example, that it wasn’t a problem with any of the mics, snake, or console. It had to have been “behind” the crossover – and that chain would include the output of the crossover itself, the cable from the crossover to the subwoofer amps. the amps themselves, the cabling from the amps’ outputs to the connector on the panel of the rack, the speaker cables that go to the subwoofers, and the subwoofers themselves.

Since ALL of the subwoofers stopped, it also can’t be anything that is specific to one cabinet or pair of cabinets. It must be something that is common to all of the subwoofer cabinets, output of the crossover, cables from the output of the crossover to the input of the amps, or (if you drive all of your subwoofers with one amp) the amp.

Think about the rate of failure in a subwoofer system. Speakers are probably the first, amps next, then cabling, and lastly crossover. Since all of the subwoofers just stopped working, and didn’t make any nasty rattling noises first, and then just started working, I’d rule out speakers. The odds of you blowing every single subwoofer at the exact same time are extremely low, plus speakers usually give some sounds of distress first. Plus, blown speakers do NOT start working again. Once they die, they don’t resurrect themselves.

Some amps have thermal protection which can shut them off until the cool enough, and then they come back on. Check the amp’s fan to make sure it’s working, and the cooling fins are relatively clean and not obstructed. It could be the connection between the output of the crossover and the amp. You can swap that out with a known good cable to eliminate this cable as the problem. You can eliminate the crossover itself by connecting the input of the subwoofer amps to the mid-bass output of the crossover (this won’t hurt anything). If the subwoofers put out sound connected this way, but not when plugged into the low-frequency output of the crossover, it could be a crossover problem. Swap it out with your spare (you DO have a spare of all of the “show-stopper” parts of your system, don’t you??).

The key here, is that you can’t actually DO any of this until it fails again, but you will at least have a plan of action in mind, and may be able to have some of the swap-out parts handy so you can cut a few extra seconds off of your down time.

Using your knowledge of your sound system components, some very basic understanding of electronics, and a lot of logic, you can quickly and easily get your system back up and running in very little time. Once you have identified a bad part – MARK IT AS BAD!! I can’t stress this enough. Nothing will take the wind out of your sails faster than the next day when you intend to repair a bad mic cable you found, you remember that you didn’t mark it, and it looks just like the other 40 mic cables in your cable trunk.

If you find a bad mic cable, slide the XLR shell back and see if there is a broken connection where the wire is soldered to the connector. If so, fix it, and also re-do the other end. When one end fails, the other end may be close behind. If both of the ends look good, cut the cable in half, and use your ohm-meter to find which half is bad. Take the XLR connector off the bad half and use it on the good half. Throw the bad half away, unless you want to spend the time to keep cutting it in half to find a good part that’s still long enough to use for anything.

Advertisements

One Response to Troubleshooting Audio Problems in Your P.A.

  1. I did not expect this on a Monday. perfect insight,. Added your site to my RSS reader.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: