Church high end sound equip.

Proximity of L.V. cabinet and H.V. cabinet's are in same room, 4 feet apart approx.

L.V. rack is supplied by ISO circuits, 120/208 3ph. PVC connections.

Dimming panel fed from same power panel.

In subwoofers,(32,000 watt Peaveys),a low end hum is present, but not always, the dimming panel when ltg. is 60% or lower adds to distortion in subwoofers at a midrange tone. The dimming panel doesn't seem to be the cause of the hum, yet it adds a higher tone of distortion.

The hum is not a great issue when system is used for music and so on. It is when the clergy is trying to speak that it is the most annoying.

Sound engineers, a few other elect. cont., and now in our lap. Many scenarios, testing, no major steps. Dirty power, ISO GRD, proximity, no definites, and we cannot produce the sound all the time, or find any differences in troubleshooting.

comment removed, didn't read the post carefully. sorry.

[This message has been edited by twh (edited 05-08-2004).]

Just to be clear:

This is not 60 Hz or some 60 Hz harmonic leaking into the sound system, but instead an increase in _distortion_ in the sound system when the lighting is at reduced power?

If the input to the sound system is totally silent, do you hear the distortion, or do you only hear distortion when there is some input (eg. someone speaking into the microphone)?

Is the distortion or noise _source_ dependant? Does it matter if you are using a microphone or a tape recorder as the input source?

-Jon

..In subwoofers,(32,000 watt Peaveys),a low end hum is present, but not always, the dimming panel when ltg. is 60% or lower adds to distortion in subwoofers at a midrange tone. The dimming panel doesn't seem to be the cause of the hum, yet it adds a higher tone of distortion.

I think you mean 3ea 2000w subs I hope! Anyway, apparently you are not a sound guy and your terms like "low end hum","adds to distortion in subwoofers" and "adds a higher tone of distortion" means very little. And what the heck is a LV and HV rack?

At any rate it sounds like there is a power quality problem probably caused by the lighting controls and possibly other systems in the building. Maybe grounding issues and low level wiring issues also. Isolated grounds were probably a waste of time.

This is going to be a tough situation to troubleshoot. I would start by shutting down the lighting system and see if that helps. It should never have been fed from the same panel. An isolated power system might be the solution. I can't understand why a competant sound contractor would not be able to get to the bottom of this.

-Hal

It is a HUM. All by itself, in the low freq. range. The dimming panel adds to it when the low freq. hum has shown itself, the dimming panel adds a mid range hum on top of the low freq. hum.

The hum is not always there. It seems after time as equip. heats up then it MAY swow up. To me it seems that there is a piece of equip. that it causing resistance and creating this low end hum to start.

Now is it a 60Hz hum? Well it seems to be. But all the equip. uses 60Hz power obviously, so it would most likely be a 60Hz hum, electricians problem now.

Could a breaker heat up and cause a hum? Loose connection? Inductive reactance?

We are thinking of bringing in a generator to get a new source of power, shutting down the rest of the bldg.

Yet, this problem shows up 85% of the time, we have been there on occasion and it doesn't show.

Last time we killed main power panel breakers one at a time, no affect. when we shut down the power to the sound equip., the hum stopped after getting fired back up and did not return in the next 1 1/2 hours while we were there. I would have thought that the heat/resistance factor would have shown up shortly after reboot.

...when we shut down the power to the sound equip., the hum stopped after getting fired back up and did not return in the next 1 1/2 hours...

Now this sounds more like could very well be a problem with the sound equipment itself. What is the history of this installation (is it new?) and the problem?

-Hal

Could it be that some of the electrical wires and some of the sound system wires are crossing near each other too closely somewhere in the building? When something electrical is turned on, could it be creating the hum through the too-close sound system wires? I understand that electrical wires and sound system wires are not supposed to be within 6 inches of each other anywhere in the run. I realize that the cabinets are 4 feet apart, but it's the wires I'm thinking about, which might be passing through a wall or ceiling side by side or within 6 inches. Somebody correct me if I'm wrong.

We got stuff all over the place!

I believe the problem has been present since day one. They are pretty sure it was always there, yet, now we show up to trblsht and it is not always present.

I feel it has something to do with the sound equip., the engineer doesn't think it is on his end. We are kind of chasing our tail in coming to a resolution. And any fix to hope you cure the problem is going to be in thousands of dollars, and will it go away?

Move sound equip. to another location? New utility transformer for sound equip.? Cement barrier wall in same room to divide? Rewire H.V., and or L.V.? And the problem is intermittent now as it is.

Anybody know of any sound sites like ECN is for us?

I'm a member over here- http://srforums.prosoundweb.com/index.php/f/6/0

Give it a try. There used to be some other knowledgeable pros there like myself but it seems they all disappeared when the board switched to this new format.

My advice still stands though. It sounds like there are multiple problems and it's going to take someone with sound system experience actually at the site to troubleshoot it. I know that you have gone that route before but whoever it was was not knowledgeable enough. A competent sound system technician should be able to determine if there are power problems and recommend a solution if they exist. This really is not the domain of an electrician because there can be many areas involved here, not just electrical. It sounds like the "engineer" is just passing the buck to coverup for his inability. Again, he should be the one to find the problem and if it involves an electrical issue elicit you to carry out his recommendations. If he can't do that I suggest turning to other sound installation companies.

-Hal

I agree that the problem really belongs to a competent sound engineer. The fact that you don't even know the frequencies of the noise is bad news from the start. The engineer should be able to prove where the noise is comming from before any repairs are attempted. Right now, it sounds like you are shooting in the dark. That can be an expensive and dangerous proposition. Locate a quality sound re-enforcement company and have them evaluate the system. You should end up with a report that says this is the problem and this is why it is a problem.

NonLinerarLoad,
Go to www.churchsoundcheck.com. You have to subscribe to the forum. The moderators are professionals and they know what thay are doing.

There are a couple of things you may want to try.
Make sure all your audio is on the same phase in the panel.
Check to see if you have a "Pin One " problem. Open up any XLR connector in the path of the problem and make sure the pin #1 is NOT connected to the shell of the connector.
Make sure the gain structure is set properly. You may want to "lift" the shield off of pin #1 on the input of the sub amp to see if this clears the problem. I'm sure your engineers check all these.
You may have a problem with the crossover. I've seen this happen before. A few components wear out and cause noise in the system.

There are MANY forums for pro audio out there. I highly suggest joining Church Soundcheck. More knowledge there than my brain can handle.(Which is not much)
Let us know what you find.

Blessings
Mark

Thanks for the input!

I will check out the sites posted. Will post here if a resolution comes about, and if I need more advice.

The system is a year old or so, it has been checked out. And of course nobody wants to pass the buck, or look as if they aren't capable of finding the problem, that includes us.

Thanks again!!!

...Hi,Non-Linear,
I just read an article in the latest issue of EC&M magazine,that deals with substantial Harmonic Distortion in a night club that rendered the bands equipment damaged and never "right" after playing there that one night..Check this out,..it could pertain to your problem at the church..Click here..>> http://ecmweb.com/mag/electric_harmonics_nightclubs_electrical
Russ

[This message has been edited by Attic Rat (edited 05-24-2004).]

OK...I used to be a DJ and a soundman....not really good at either but here is a idea...

how many amps are you running?..i mean sound amplifiers...is it possible to disconnect all inputs going to the amplifiers ?...if so, try that and see if you can eliminate half the equipment...if the hum does not stop, try a different circuit for the amplifiers...next, check the sheild on the cables going to the speakers...you can use an ohm meter for this and since the problem is intermitent, move and shake the cord while securly attached with the ohm meter as moving the test leads around during ohm checks can cause fluctuations...is cables are good and amplifiers are good then it must be a power problem must likely a ground-loop of some kind....i had an amplifier one time that did this and to see if it was the amp or the power , I pluged a two prong adapter in the wall then plugged in the amplifier...in a sence, disconnecting the ground prong on the amps plug...the noise was gone....but I am not convinced this is your problem...but try it.

also....if you can time the hum, it will give you a good idea as to what might be causing it....sometimes I have seen the cooling fans inside sound equipment kick on and cause a hum...and I have seen a refridgerator do the same as the compressor kicks on...air conditioners, lights and other things can cause these problems so don't limit your self to your power supply and sound equipment....

also keep us updated as I want to know what the bugger is...

Thanx , Mike

me again...just wanted to say I am aware of my bad spelling so don't bother filling this post with rhetoric about my poor spelling !!!

Thanx

In the sound biz, there is a hi tech term for a 2 prong adapter - it's called a "ground lift". And it may actually eliminate a buz, so try it. You can try it at the sound board also, a possible source for noise. If it helps, this just points to some grounding problems in your line voltage system.

Radar

Here's another resource you can try:
www.churchproduction.com

Good luck, and please let us know what you find out.

Radar