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Author Topic: "pops" in Powered Speakers?!  (Read 4344 times)

Adam Sabo

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"pops" in Powered Speakers?!
« on: October 22, 2008, 11:22:19 am »

Hello All,
I have been on this forum once before when we were looking to put some new components in our new sanctuary. I have been asked by others to let you know how things turned out, so I will do that below.
As for now, I have a question... We are having a problem with electrical cackle/pop noises in the powered speakers when the furnace kicks on or when we turn up the speed on the dimmer switch for the ceiling fans only. The speakers are Yamaha MSR400's and I talked with a Yamaha tech earlier in the summer about it. At that time we had only noticed the Fan switch problem. Now that it is getting cooler, the new furnace kicks on during service and it is picked up in the speakers too. Yamaha said to me with regard to the fan, it was a sine wave switch problem and that I would have to replace the dimmer switch. I tried to research that, but I can't find any info about varieties of switches. And now with the furnace coming on I have to figure this out soon. An additional note, during thunderstorms in the summer, we would pick up electrical noises too. Any direction in this area would be great.
The main house speakers are the MSR400's. They are not coming into contact with the fan's electric cable or the furnace electric cable. They are not sharing a breaker in the breaker box. We have no problem with other electrical feed back for lights or other things plugged into the wall. The speakers and projector are plugged into an outlet that is up in the rafters and is turned on and off by a switch on the sound booth wall. The church was "Stick Built" but has a metal roof.
Let me know what else you need to know about the set up.
For those interested in what we ended up getting I will mention that below...




I posted a thread called "Sound System ideas needed..."
I got lots of info and feedback and we were able to do quite a bit for what we had for a budget. Certainly not Pro by any standard, but great for small country church.
index.php/fa/326/0/

We already had:
some nice shure pulpit and choir mics
many spools of cable (Audio and VGA)
Extron video switcher (and signal booster)

We bought:
Yamaha MSR 400's as main speakers
Mackie - CFX20.mkII mixer
Squire 12" floor monitors (extremely cheap but very effective)
Berhinger XM8500 mics for worship team (also cheap, but great reviews for cheap mic)
spl meter
music and mic stands
dual channel DI Box
3 recessed stage boxes (8 xlr and I added 2 monitor jacks in each one)
bunches of connectors for XLR and 1/4" and cable
NEC VT700 projector
I just ordered a AT 3000 series wireless mic system (not here yet)

As mentioned we were given the cable by a friend and were told to sell any extra we didn't use to buy A/V components we didn't have. The only thing we have left over are 2 rolls of Plenum VGA cable about 500 feet each. And some JBL ceiling speakers. Would a local A/V company buy something like this? Is there an A/V classifieds online? I don't know how to go about doing that.

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Keith Shannon

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Re: "pops" in Powered Speakers?!
« Reply #1 on: October 22, 2008, 12:39:45 pm »

If a powered speaker, on a completely different circuit from the furnace/dimmer, is picking up interference, suspect number 1 is shielding of signal lines. Suspect number 2 is dirty power induced in the entire building by the furnace/dimmers, and suspect 3 is the speakers themselves.

Step 1: Verify that the cables used to send the output from your mixer to your powered speakers are actually instrument cables, not speaker cables. Sounds counter-intuitive, but this is because "speaker" cables are designed to carry high-wattage, low-impedance signal between the amp and an unpowered speaker cab. Since the amp and cab are one unit, what you're sending from the mixer is signal-strength, which is milliwatts instead of hundreds of watts, and has very high resistance on both ends. Such a circuit is highly vulnerable to EM interference and so the cable must be shielded. I think however that the furnace kicking on would be the least of your worries if this were the case; you'd have 60-cycle hum coming from every power cord and transformer in the room.

Step 1a: If you can use a balanced signal line (XLR, used for microphones) between the board and amp, that's better than using a shielded instrument cable. In such a cable, the ground is completely separated from the signal circuit (in an unbalanced line, the ground side of the signal also forms the shield) and as such there is little if any interference that may otherwise occur in an unbalanced line where noise on the ground side affects the signal side, a phenomenon I usually hear referred to as "backwash".

Step 2: Verify that the cables used are as short as is feasible. Long runs of cable, even shielded, pick up more noise. The problem is compounded further if you have a much longer cable than necessary and are coiling it; a coil picks up EMI from every direction. Use only what is necessary.

Step 3: Try changing the angle at which the cable is situated to the furnace. Just like a radio antenna, you get better reception when the antenna is pointed one way versus another. The only difference is that here, you want the worst possible reception because what you're picking up is undesired noise.

Step 4: Look for a "ground lift" switch on the powered speakers. This switch governs where the noise collected by the shielding is shunted to. There are two types; in both cases the difference is usually between using the third prong as the ground (suitable for most electrical wiring setups) or one of the "hot" prongs (suitable with older or outside wiring that may not have proper grounding). Basically, try any available setting and if the noise is lesser with one setting over any other then use that setting. If that happens to be the "lift" setting, get with whoever's in charge of the building to see if the grounding on that circuit or in general can be improved as indoor wiring should not have this problem.

Step 5: There are a few different types of dimmer switches. The main difference is whether digital or analog. An analog dimmer is basically just a potentiometer; it reduces wattage by providing some variable amount of resistance to current flow. These are USUALLY pretty noiseless, though a cheap one can buzz. A digital dimmer works by turning the current on and off very quickly, and varying the ratio of on time to off time. These can produce EM "clicks" as they turn on and off, which, because they happen so close together, comes across as a buzz. Your average home dimmer, for instance one that comes in a fan with a remote control, will buzz; higher-quality dimmers will usually mention low EMI as a feature; these will ameliorate the problem with the dimmers, but not the furnace.

Step 6: Try putting a power conditioner between the wall outlet and the powered speakers. Even if the equipment is on a totally different circuit, there's probably one line coming into the building from the grid, and even the grid, when it comes down to it, is all one circuit. A power conditioner will remove noise inherent in the current of the power supply itself, so called "dirty power". A simple surge strip may do a little of this, but an actual power conditioner goes much further. Practically every professional musician uses power conditioners for their amplifiers for this same reason.

Step X: Return/exchange the powered speakers. There may be a fault in their grounding/shielding, or they may not have any at all. There's two types of shielding; what works well against EMI static, and what works against 60-cycle hum emitted from powered equipment. These speakers need work on one or the other.
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Adam Sabo

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Re: "pops" in Powered Speakers?!
« Reply #2 on: October 22, 2008, 11:33:44 pm »

Thanks Keith for all your time in answering this question. I am using XLR cables from the mixer to the powered speakers, but they do have a some extra length since I didn't think it would hurt it to be spread out in the rafters. I will re-arrange the xlr lines, then I may try a power surge strip just to test if it reduces the noise and by that perhaps diagnose if its "dirty power". I'll just work my way down the list. Thanks again for the helpful advice!
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Kent Thompson

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Re: "pops" in Powered Speakers?!
« Reply #3 on: October 23, 2008, 12:43:27 pm »

Power strips in general do not provide power filtration only protection from surges. You have to spend some bucks to get filtration. Check for cables running near or with power lines if they are move them.

Probably the first thing to do though is find out where in the system the noise is getting in at. Start with just the amps powered up and disconnected from the rest of the system. If there is no noise there, connected up the next thing in line etc. till the noise appears. Then you know where in the system the noise is getting in and your choices of what could be wrong gets narrowed down significantly.
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Adam Sabo

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Re: "pops" in Powered Speakers?!
« Reply #4 on: October 23, 2008, 07:42:57 pm »

Today I tried a couple things to try and isolate the problem. The first thing I did was unplug the XLR feeds in from the back of the powered speaker. Then I tried turn on the fans and the furnace to create the noise in the powered speaker to see if it was strictly electrical. Well that created no noise in the speaker. So it sounds like it is not "dirty power".
Next I ran an xlr cable from the mixer's "Main outputs" into the back of the powered speaker. (in other words, straight from the sound booth to the speaker across the middle of the sanctuary) Then I tested it all again. This significantly reduced the "pop" from the fan dimmer switch. And eliminated the furnace "pop" altogether.
So it seems to be in the XLR lines from the mixer to the powered speaker. They run from the mixer, under the sound booth, up through pvc conduit (shared with other A/V cables), then free-span across the trusses and then drop down through the ceiling above each of the speakers. I moved them around a bit in the truss area today, but it didn't solve the "pop". Is there another way to shield these lines?
Thanks.
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Arnold B. Krueger

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Re: "pops" in Powered Speakers?!
« Reply #5 on: October 24, 2008, 11:23:11 am »

Adam Sabo wrote on Fri, 24 October 2008 00:42

 Is there another way to shield these lines?



Steel couduit can help, and its not that bad to install for straight runs.
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Adam Sabo

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Re: "pops" in Powered Speakers?!
« Reply #6 on: November 04, 2008, 03:57:59 pm »

hi all,
I believe the problem is solved. My father-in-law who is an electrical engineer came by to do some tests with me on the sound system. I happened to have 1 braided Shield xlr mic cable, and by using that we eliminated the pop. Everything else we tried using a non-shielded xlr mic cable still had a Pop. I have running out of the mixer to the powered speakers regular mic cables. They were balanced lines, but not shielded. My understanding was that wouldn't be an issue, so that is why I never mentioned it in the original post. But the impedance coming out of the mixer is low(150 ohms), while the impedance coming into the speakers are very high (10k ohms). Anyway, I am planning on running xlr cable that has a foil shield and trusting that it will be enough shield for the job. Thanks everyone for your input. God Bless you.
Adam
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Jerrybosun

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Re: "pops" in Powered Speakers?!
« Reply #7 on: November 05, 2008, 11:16:14 am »

A "Non sheilded" XLR cable?  It sounds like someone used the old speaker cables for a line run. This would be one problem you could not trouble shoot over the internet!
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ProSoundWeb Community

Re: "pops" in Powered Speakers?!
« Reply #7 on: November 05, 2008, 11:16:14 am »


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