Redoing the Sound System.

[techie09]

Before I begin I want to apologize if I sound vague. I am just trying to get the basics set up right now. If you need me to supply more information, I can.

I recently started working in a high school theatre as the TD. When I got there it was a mess (that's putting it lightly). I am working on moving the soundbooth downstairs to a front of house position. It is currently in a sound proof room. Yes, that's right, a sound proof room. So, how I am going to manage to do this for now, is to place our mixer in the back of the house (or middle of the house, when the cafeteria wall is open - yes it's one of those kinda places). Then I am going to run a couple of XLR lines (like 5, for main speakers and a couple for "patching") i'll add some 1/4 lines later. In my mind this worked good, and we tried it out and it worked fine. But one problem that I see us having is problems with power. I am no expert in the 'power field' by any means - I just know the basics.
All of the amps to power are speakers are upstairs in this soundproof room. There is a temping power outlet right under where my console is going to be. In addition to having to run those XLR lines, should I also run an extension cord or two? If I did I would probably have to run it separately to avoid it interfering with the audio cables, right? Also, to power my wireless mics, cd players, etc. I would probably want to use the same power from upstairs, or could I get away with plugging it in to that outlet downstairs? Any suggestions or comments would help alot! Thanks!

 

[kiwitechgirl]

To avoid hum issues, sound systems should all be run from the same, clean, power source. So, run an extension cord from wherever your amps are powered from.

 

[techie09]

To avoid hum issues, sound systems should all be run from the same, clean, power source. So, run an extension cord from wherever your amps are powered from.

Ok, thanks. This is what I thought.

 

[BillESC]

The draw for your mixer and wireless mics is minimal, there should be no hum issues running your extension cord along your mic cables. Be sure to use quality mic cables.

 

[mixmaster]

Before I begin I want to apologize if I sound vague. I am just trying to get the basics set up right now. If you need me to supply more information, I can.

I recently started working in a high school theatre as the TD. When I got there it was a mess (that's putting it lightly). I am working on moving the soundbooth downstairs to a front of house position. It is currently in a sound proof room. Yes, that's right, a sound proof room. So, how I am going to manage to do this for now, is to place our mixer in the back of the house (or middle of the house, when the cafeteria wall is open - yes it's one of those kinda places). Then I am going to run a couple of XLR lines (like 5, for main speakers and a couple for "patching") i'll add some 1/4 lines later. In my mind this worked good, and we tried it out and it worked fine. But one problem that I see us having is problems with power. I am no expert in the 'power field' by any means - I just know the basics.
All of the amps to power are speakers are upstairs in this soundproof room. There is a temping power outlet right under where my console is going to be. In addition to having to run those XLR lines, should I also run an extension cord or two? If I did I would probably have to run it separately to avoid it interfering with the audio cables, right? Also, to power my wireless mics, cd players, etc. I would probably want to use the same power from upstairs, or could I get away with plugging it in to that outlet downstairs? Any suggestions or comments would help alot! Thanks!

First thought, how permanent is this set-up going to be? If this is something you do for an evening, and then strike stuff, an stringing extension cord is fine, assuming it is the correct size and stuff. If this is any sort of a permanent install, or even something that you leave up between a string of events, local electrical codes may frown on using extension cords for this application.

Second thought, in an ideal world all the power for the audio would come from the same source to prevent things like ground loops. In reality, if your system runs clean on power from the plug that's convenient to the new location, and you are comfortable knowing what else is on that circuit, and where the breaker is, I'm always in favor of not using any more extension cord than needed. Cords get tripped over, damaged, unplugged, at the least convenient times. If you can, use the local outlet and save running that extension cord. You may not have hum problems. I have one venue on my campus that the FOH mix positon, booth mix position, SL amp circuits and stage power all come from separate panels, and at least the FOH and Booth positions are on a separate building feed. We still get clean audio.

 

[museav]

A very easily misunderstood issue and one that has other consideration since it get into areas that also involve codes and licensed engineer/contractor.

NFPA/NEC definitely frowns on, actually prohibits, extensions cords used for permanent power. So if the location is considered permanent then that may not be an option.

You also need to somewhat separate grounding and power, the two are very closely related but also address two different issues. A good resource on grounding for AV systems can be found here, Middle Atlantic Products - White Paper. Parts of this paper are rather technical but it also addresses most of the important issues on a very practical basis.

Having all the audio power served off one distribution panel can be beneficial for several reasons but is not by itself the issue, is not always practical (especially when addressed after the fact) and as mixmaster noted, is not always necessary for a successful system. Due to it being an existing space, I recently finished up a large audio system project that has anything on stage powered off one electrical distribution panel, the mixing, processing and amps off another distribution panel next to that and the integrated recording/production portion of the system getting its power off yet a third panel located in a completely different part of the building and yet the system has no noise problems even in an extremely quiet space or on high quality recordings.

 

[Studio]

Then I am going to run a couple of XLR lines (like 5, for main speakers and a couple for "patching") i'll add some 1/4 lines later.

You might want to get an audio snake.

 

[SHARYNF]

A very easily misunderstood issue and one that has other consideration since it get into areas that also involve codes and licensed engineer/contractor.

NFPA/NEC definitely frowns on, actually prohibits, extensions cords used for permanent power. So if the location is considered permanent then that may not be an option.

You also need to somewhat separate grounding and power, the two are very closely related but also address two different issues. A good resource on grounding for AV systems can be found here, Middle Atlantic Products - White Paper. Parts of this paper are rather technical but it also addresses most of the important issues on a very practical basis.

Having all the audio power served off one distribution panel can be beneficial for several reasons but is not by itself the issue, is not always practical (especially when addressed after the fact) and as mixmaster noted, is not always necessary for a successful system. Due to it being an existing space, I recently finished up a large audio system project that has anything on stage powered off one electrical distribution panel, the mixing, processing and amps off another distribution panel next to that and the integrated recording/production portion of the system getting its power off yet a third panel located in a completely different part of the building and yet the system has no noise problems even in an extremely quiet space or on high quality recordings.

If the ground system is done such that there is a "green wire" from each outlet back to the panel, and the outlets are of the isolated ground variety this works. What I have found is that in a lot of cases people are using the steel conduit as the ground along the way by not using isolated outlets , and as things settle and corrode, problems start to become audible.

Sharyn

 

[TimmyP1955]

If all of the outlets you are using are fed from the same breaker box (meaning that they all have the same ground reference), there is a good chance that you will have no problems. Such is the case at my venue even with a console that I expect has "the pin 1 problem".

 

[museav]

Maybe some misunderstandings. While it was common in older residential electrical systems, thus there being receptacles with no ground pin, it is no longer legal to use the conduit system as the ground path, there has to be a dedicated safety ground conductor. That safety ground conductor is the green wire, an isolated ground system actually requires a separate conductor (thus four wires), a dedicated, insulated bus bar in the distribution panels, etc. The isolated and safety grounds do eventually tie together but only at one point at the service entrance or main panel.

All circuits in a building have the same 'ground' reference as there should be only one ground point for any electrical distribution system. However, being on the same distribution panel does not guarantee that two circuits have the same ground path and thus there can be some potential (voltage) between them. Having circuits on the same panel can increase the chances of having no potential or at least minimize the differences, and thus is a good practice, but at a receptacle you tie the safety ground conductor to the metal gang box which may be attached to a metal stud that touches ductwork and piping which touches another wall and box which is on another circuit or panel and so on, thus there are many different possible ground paths and from that, the possibility of a voltage difference between any two safety ground points in the building even if tied back to the same panel. Expand that to all the receptacles and distribution panels in a typical electrical distribution system and you can see that any receptacle may have several possible ground paths and a ground potential relative to any other receptacle. That is the purpose behind an isolated ground system, it provides a dedicated ground path that is not compromised by other connections, or a mesh or 'swamp' ground system where you ground at so many points as to not allow there to be any significant potential between any two points.

 

[SHARYNF]

the outlets I am seeing more here in the "wilds" are
Installing an Isolated-Ground Receptacle
It does not appear that in retrofit installs a solid bare copper wire is being pulled a connection of the conduit via a copper wire at the outlet and at the panel. Again might very from location

NEC requirements of isolated ground (IG) wiring

On most of the outlets I am familiar with the ground even if it has a dedicated green wire back to the panel, has the ground connected to the outlet box via the mounting screw and thus connects the ground to the conduit system assuming a metal conduit and a metal outlet box (most residential systems these days use plastic boxes so it is not a factor Again maybe not in a typical system, but in my experience, it is the metal conduit connections that have on occasion seemingly been the cause of a lot of the ground problems.

Again your mileage.....

Sharyn

 

[museav]

That is the exact problem, the safety ground ties the receptacle ground to the box that ties to the rest of the raceway system and so on. And that is the very reason for an IG system where the receptacle ground connection is via a dedicated Isolated (or Insulated) Ground conductor and that conductor and connection are insulated from the safety ground and raceway system except at one point (see Page 17 in the Middle Atlantic paper).

It can get very confusing, for example you can have an IG system by using standard receptacles in the racks, insulating the rack from the electrical raceway and structure and using the IG conductor for the power and rack ground in the rack (see Pages 30, 31 and 32 in the Middle Atlantic paper). Thus you have an IG system with equipment plugging in to standard outlets, although the rack connects to an IG receptacle.

I do find that the biggest problem with IG systems is maintaining their integrity, all it takes is a non-insulated tech/isolated/insulated ground bus bar in a distribution panel or a jumper from receptacle ground to the box at one box to short circuit an entire IG system. Thus many "IG" systems are not really IG and it is not necessarily easy to test, you can temporarily disconnect one of the grounds where they come together and that should cause the resistance between the ground pin at a receptacle and the raceway system to go from very low to open, if it does not then the IG system is compromised, but disconnecting a ground is not something you want to randomly be doing.