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Author Topic: Wireless outdoor speakers on lamp posts  (Read 15371 times)

Bradford "BJ" James

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Re: Wireless outdoor speakers on lamp posts
« Reply #30 on: October 28, 2010, 02:16:51 pm »

double post
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Charlie Zureki

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Re: Wireless outdoor speakers on lamp posts
« Reply #31 on: October 28, 2010, 02:19:30 pm »

Hal Bissinger/COMSYSTEC wrote on Thu, 28 October 2010 12:20



 Hello Hal,

Quote:

Yes, that's true in most states. What you don't understand is that it is wiring within a structure or building. Now, I'm not going to bet the bank on that statement because I'm not familiar with Michigan but I have never seen any requirement for an EC to hang wire on public or private poles or bury it in the ground.


  Yes, I do understand... but, as you've said, you're "not familiar with Michigan".

 It is against State Ordinances and most local codes to hang anything on Public Lighting Poles, without expressed written permission from the County of Jurisdiction.

 If it is a Public Utility Pole, consent must be sought from that Public Utility. (There are hefty fines that can be levied if there is no consent)

 Private property is another story, although there can be specific codes also that may pertain to the intended use or items to be hung.

 Burying any wire or cable is addressed in the State Codes.  Nec codes have also been adopted by the State of Michigan as "State Code".  Example: Low voltage cable must be buried at a minimum of 6". Where the low voltage cable passes through concrete, it must not be incorporated into the concrete, but pass through conduit buried in the concrete.



Those are long runs, and the tension and weight on the cable and guide wires will be pretty high.

Quote:

That may or may not be a problem depending on what the lamp posts are capable of supporting. You are talking about two speakers and two cables hopefully 180 degrees from each other that will cancel out the tension in the post. When linemen design this kind of stuff all the tensions and loads are considered to minimize lateral loading on the poles. That's why you will see down guys and pole to pole guys in addition to the actual cable. You don't say, but what are the poles made of? Wood, steel, spun aluminum?

-Hal




 
Exactly, it may be a problem, and that's why I mentioned it.  When these Engineers spec out the Poles and means of fastening the pole to the ground, they are concerned with the weight of the pole, wind load, and the tension and weight of any cables to or from it.

  They are not necessarily considering  that someone may add an additional 100lbs  or more of weight,(at the end of a lever),  the additional tension and the added wind load, especially, if it's a street lighting pole and NOT a Public Utility Pole.

  Here in Michigan, it is very common to have lighting poles that are only 16 ft and 20ft high and made from materials such as plastic, fiberglass, aluminum, wood, cast concrete, steel, cast iron, etc...

  Our highway lighting poles are generally 60ft. high or more, as well as lighting poles in major Shopping malls, car parks, or large office complexes.

  Cheers,
  Hammer
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Bradford "BJ" James

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Re: Wireless outdoor speakers on lamp posts
« Reply #32 on: October 28, 2010, 02:46:54 pm »

Hal, Charlie et all,
I was being a bit generous with my distances. Distance from pole to pole is 100-120'. I was adding a bit extra since the existing unused insulators the electricians will be using are near the tops of the poles, and the cables will have to come down about 20' to their mounting location. So, not all the distances quoted are suspended.
The poles are concrete and steel and the company running the cable is experienced. I'll make sure to ask when I quote them what cable to use, that they are able to safely install it.
Also, looks like my max run will be 22 units. So that brings my total load to 660 watts assuming I use 30 watt taps on all units.

But, back to my question: is 12g UTP going to be sufficient for this straight run?

Pertinent info:
Run "A"- Max potential distance 2500', 660 watt load, driven off one channel of a 2x 1200 watt amp(69.v)
Run "B" will be less right now, but potentially the same as "A" in the near future.
Thanks
BJ
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Hal Bissinger/COMSYSTEC

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Re: Wireless outdoor speakers on lamp posts
« Reply #33 on: October 28, 2010, 08:06:35 pm »

Trying to think of how to calculate it. Somebody smarter in math than me might be able to help out. What is going to happen is that if you make every speaker 30 watts, as you get farther and farther away from the amp the accumulating load and the resultant cable voltage drop will give you progressively less and less than the selected 30 watts. What you can do is use lower wattage taps at the begining and progresively higher wattages as you go along to the end to equalize. I would like to come up with a spreadsheet to determine the optimal wattages for each position as well as showing the effects of different wire gauges and thereby answer your question but it ain't working. Confused

-Hal  

Bradford "BJ" James

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Re: Wireless outdoor speakers on lamp posts
« Reply #34 on: October 28, 2010, 08:42:00 pm »

Hal Bissinger/COMSYSTEC wrote on Thu, 28 October 2010 20:06

Trying to think of how to calculate it. Somebody smarter in math than me might be able to help out. What is going to happen is that if you make every speaker 30 watts, as you get farther and farther away from the amp the accumulating load and the resultant cable voltage drop will give you progressively less and less than the selected 30 watts. What you can do is use lower wattage taps at the begining and progresively higher wattages as you go along to the end to equalize. I would like to come up with a spreadsheet to determine the optimal wattages for each position as well as showing the effects of different wire gauges and thereby answer your question but it ain't working. Confused

-Hal  

I appreciate your comments Hal.
A vendor suggested I might use 2 pair UTP and split the run about 2/3 down. What do you think of that?

And, now that I have the official proposal in front of me, it looks like the actual distance of my long run will be closer to 1800' give or take.
Would you be comfortable running 12g this distance?
Like you say, I could to the progressive tap down the line too.
Thanks,
BJ
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John Roberts {JR}

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Re: Wireless outdoor speakers on lamp posts
« Reply #35 on: October 29, 2010, 12:25:25 am »

Bradford "BJ" James wrote on Thu, 28 October 2010 13:46

Hal, Charlie et all,
I was being a bit generous with my distances. Distance from pole to pole is 100-120'. I was adding a bit extra since the existing unused insulators the electricians will be using are near the tops of the poles, and the cables will have to come down about 20' to their mounting location. So, not all the distances quoted are suspended.
The poles are concrete and steel and the company running the cable is experienced. I'll make sure to ask when I quote them what cable to use, that they are able to safely install it.
Also, looks like my max run will be 22 units. So that brings my total load to 660 watts assuming I use 30 watt taps on all units.

But, back to my question: is 12g UTP going to be sufficient for this straight run?

Pertinent info:
Run "A"- Max potential distance 2500', 660 watt load, driven off one channel of a 2x 1200 watt amp(69.v)
Run "B" will be less right now, but potentially the same as "A" in the near future.
Thanks
BJ



While not very elegant this sounds like one I would try to do with an excel spread sheet.

Look up the ohms per foot for 12ga  (.00187 ohm) or whatever size wire you want to use, then multiply that times the span between speakers (120') to get the wire R per leg (.224 ohm). Then calculate the effective impedance of a 30W/70V tap (hint = 163 ohms) .  So the far last leg is delivering  163/163.224 of the voltage to the speaker as is present at the beginning of the run, for a - ,012 dB drop in voltage. Now this is additive, cumulative, etc.

Ok the next to the last leg has this 163.224 ohm load sitting in parallel with the 163 ohm drop so loss will be -.022 dB, loss at the last speaker is now -.033 dB


=====

But I am not a human spread sheet so fast forward to the back of the envelope.. 30 x 163 ohm loads is 5.4 ohms..   or approximately -0.35 dB drop in that first span.

I'm guessing (hoping) the average drop is half that so .17 db x 30, or around  -5 dB at the end (that makes your last 30 watt speaker sound more like 15W or less.

I would really load up a spread sheet and do the individual span math because you will probably find the wire gauge matters more at the the start of the long run than at the end, and stuff like that..

Then if you tweak the the taps for more output at the far end, the spread sheet could show you have it impacts back up stream.

The sharp pencil part comes in with cost of thousands of feet of whatever gauge vs. pushing the system to higher voltage for lower losses.



JR

 
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Bradford "BJ" James

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Re: Wireless outdoor speakers on lamp posts
« Reply #36 on: October 30, 2010, 01:02:05 pm »

Thanks JR. That helps.
Cheers.
BJ
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