Print Page - Wireless outdoor speakers on lamp posts

Smalltown mainstreet is looking to install an outdoor wireless speaker system to play background music and possibly make announcements for special events. I am not aware of anything that would be suitable for this application. We have harsh winters and this system would be used 4 seasons. A previous proposal in a different town I have seen has indicated heaters be installed for each unit. I just see so many points for failure in a system like this, but not sure how a simple 70v system could be run due to the cables.
Suggestions?

Funny thing is, right now they have about 6 crappy bookshelf speakers mounted on the posts with about 1000' of cheap zip wire run from one post to the next. An old discarded home stereo is supplying the music from one of the stores. One of the local shopkeepers set this up himself, and I'm surprised it still works as well as it does....though not much level in the last few speakers.)

If they're running zip cord pole to pole and it's acceptable, why can't they run proper wire for a 70v system pole to pole?

The zip cable isn't acceptable. It works but it's not correct. Is there a speaker cable that could be used for 70v that would be able to be stretched like that? My only other concern is that they may want it run across a stoplight intersection where we won't be allow to run overhead cables.

Obviously the lamp posts have power to them for the lamps but is there accessible power for an amp, RF receiver, etc. at every post? If not, then wireless seems pretty much impractical unless somebody wants to be constantly recharging or replacing batteries.

If you have power at a minimum of one pole on each 'block' then you could use a single wireless transmitter and then for each 'block' have a receiver and amp that serves the speakers on that block. I believe that some people have used some of the Lectrosonics wireless systems for this type of application. You might indeed need to have some type of environmentally conditioned space for this, heating may an issue but so may be keeping everything dry including from condensation on the inside of any enclosure if the electronics get warm while it is cold outside.

Brad,

With all due respect, I would forget the wireless speaker idea. I doubt you'll even find a wireless speaker that will hold up to the weather. Secondly, all the effort around A/C and wireless signal distribution is going to be a hell of a lot more work than running good speaker wire no? Check with the town, perhaps there is pole to pole conduit run underground you could use? If not, can you span wire rope taught from pole to pole and then attach the speaker wire to it? Sort of like a tight rope? Lastly, there are plenty of good sounding and extremely durable outdoor professional speakers to choose from - and will offer you far more options than anything wireless.

ScottH

Hey, you're preaching to the choir here. If they insist on going the wireless speaker route, I was planning on extricating myself out of the situation.
This just came out of left field at me yesterday so I haven't had a chance to see if there were any realistic candidates for the wireless setup. I'm imagining that they are probably thinking about those wireless garden speakers you can buy at Walmart. Probably do up the whole town for a couple hundred bucks lol.
Underground conduit would probably be too good to be true, but I'll check into that.

BJ

edited for spelling

Perhaps some confusion as I did not suggest wireless speakers, in fact I said they were likely impractical. However, BJ's one post stated there is part of the run where a wired connection may not be an option, so what I was suggesting was possibility of multiple wired subsystems with a wireless link between them or from a common source. An amp and receiver for each susbsystem could be located at the first pole in each subsystem or in a nearby building or enclosure.

Lectrosonics makes wireless mics and IFB systems using their digital hybrid technology. These do not use companding and thus are typically better suited for wireless transmission of music. It's a pretty common approach to use their systems as wireless audio repeaters.

The underground conduit approach may be a good one if it is empty conduit or used just for signaling cable. If the conduit is also used for Class 1 or similar power wiring then code prohibits running multiple Classes of cable in the same conduit or raceway. If there is an open conduit you may want to consider direct burial or water resistant cable.

There is cable made for overhead suspension called messenger cable that has a dedicated suspension wire effectively 'siamesed' with the signal cable, however I can't find a simple single twisted pair version. Plenty of coax versions and some UTP/CAT versions that you might be able to use.

Hello,

This is another case where someone knows a bit of information... except, they don't understand that using a less that commercial grade equipment is NOT ACCEPTABLE.

They want something ...CHEAP and don't want to pay the real cost of a proper system.

Hammer

Charlie Zureki wrote on Thu, 09 September 2010 09:24

Hello,

This is another case where someone knows a bit of information... except, they don't understand that using a less that commercial grade equipment is NOT ACCEPTABLE.

They want something ...CHEAP and don't want to pay the real cost of a proper system.

Hammer

That's a given.

Bradford "BJ" James wrote on Thu, 09 September 2010 11:33

Charlie Zureki wrote on Thu, 09 September 2010 09:24

Hello,

This is another case where someone knows a bit of information... except, they don't understand that using a less that commercial grade equipment is NOT ACCEPTABLE.

They want something ...CHEAP and don't want to pay the real cost of a proper system.

Hammer

That's a given.

Hello Bradford,

Stick to the "Do it right" plan. They'll find some ahole to do what they THINK they want...then you'll get the job in a few years to clean up their mess...

Hammer

Charlie Zureki wrote on Thu, 09 September 2010 12:38

Bradford "BJ" James wrote on Thu, 09 September 2010 11:33

Charlie Zureki wrote on Thu, 09 September 2010 09:24

Hello,

This is another case where someone knows a bit of information... except, they don't understand that using a less that commercial grade equipment is NOT ACCEPTABLE.

They want something ...CHEAP and don't want to pay the real cost of a proper system.

Hammer

That's a given.

Hello Bradford,

Stick to the "Do it right" plan. They'll find some ahole to do what they THINK they want...then you'll get the job in a few years to clean up their mess...

Hammer

Ya, I'm afraid history will repeat itself.
http://srforums.prosoundweb.com/index.php/m/555388/5162/#msg _555388

There is cable made for overhead suspension called messenger cable that has a dedicated suspension wire effectively 'siamesed' with the signal cable, however I can't find a simple single twisted pair version.

Look at IMSA cable. That's what's used for traffic signals and you should have no problem finding a 12/2 version with a messenger. You couldn't ask for a better cable for this. Be sure to get the proper support and attachment hardware for the cable you buy. There is hardware to attach the cable to the light posts as well as the 70v speakers to the light posts. As for that intersection, betcha there is a way to run overhead to get around that also. You just need someone who knows what they are doing.

But then all this runs counter to what they think a job like this involves and should cost.

-Hal

If there are buildings nearby, instead of trying to engineer a distributed system on lamp posts, why not design a more long throw system from buildings that could cover the same areas? For example, you could mount weather resistant long throw full range loudspeakers (like those used in stadium end zones or on top of press boxes) to some buildings and then be able to run cables inside, or across the roofs. Would require less speaker locations, and cover about the same area, if you have some good speaker mounting positions.

I used to do a distributed speaker array for a hotel's fireworks show. It required us to run thousands of feet of wire (as we didn't trust any wireless systems at the time for something so important) and took forever to install, and dismantle every year.

One year, we decided to try the area approach, and put large PA speakers on a few roofs. While we still needed to put a few delay speakers around, we saved a ton of delays, and cable, and got better coverage.

So, while a bigger weatherized speaker will cost more, it will cost less to rig and wire that a bunch of smaller pole mounted ones, saving money on the install, and total project.

And, now there are some pretty good sounding weatherized long throw speakers available, like the Community R series, so you won't sacrifice a lot (if any) of fidelity.

That's some great idea's guys. Thanks very much.
BJ

Hal Bissinger/COMSYSTEC wrote on Thu, 09 September 2010 22:15

There is cable made for overhead suspension called messenger cable that has a dedicated suspension wire effectively 'siamesed' with the signal cable, however I can't find a simple single twisted pair version.

Look at IMSA cable. That's what's used for traffic signals and you should have no problem finding a 12/2 version with a messenger. You couldn't ask for a better cable for this. Be sure to get the proper support and attachment hardware for the cable you buy. There is hardware to attach the cable to the light posts as well as the 70v speakers to the light posts. As for that intersection, betcha there is a way to run overhead to get around that also. You just need someone who knows what they are doing.

But then all this runs counter to what they think a job like this involves and should cost.

-Hal

Hal,
Looks like I will be providing a quote for a wired system now.
Thanks for the info on the cable. Do you know of a supplier of this cable and clamps? The IMSA website doesn't have any listed or links to suppliers, and I have searched online. I have a few calls in to my cable vendors, but I doubt they carry this stuff.
Thanks,
BJ

Power and Tel Used to be Clifford of Vermont.

IMSA cable page

-Hal

Hal Bissinger/COMSYSTEC wrote on Thu, 07 October 2010 17:28

Power and Tel Used to be Clifford of Vermont.

IMSA cable page

-Hal

Thanks Hal,
I scoured the net for hours and couldn't find this.
Off to do some reading now.

BJ

Couple more questions.
http://www.ptsupply.com/pdf/Catalog/Wire%20&%20Cable/IMS A.pdf

On page 6 of this chart- is this the cable I need? My main concern is that it is solid copper, and I would want to use stranded.
The town has a commercial electrical contractor they use. They will look after supplying the cable, and installing it. I just have to tell them what to use. I guess if we can't find the proper messenger cable, I could get them to run wire lashing and attach the cable of my choice.

Also looking for some advise on the maximum distance I can go.
Amps and controls will be in a central location. Cable has to run across the street then branch off 1)up the street 3 blocks potentially 30 units 2) down the street 3 blocks with another potential 30 units. Amp will be a 2x 1200watt amp, so the total speaker load using 30 watt taps leaves me some room.
We're talking about a half mile in each direction. What IS the maximum I could go? -for future reference. If they were to go further in the distant future what do you do for runs of a mile or more?
Thanks,
BJ

bumped to add that I presume I would want to run twisted pair for this....which takes the messenger cable I mentioned out of the picture.
BJ

Those pages are a little confusing. There is a lot of twisted pair available but they just give the spec, not what wire gauges are available. You don't absolutely have to use twisted pair but it would be nice. Give P&T a call and ask them for information. As for distances, you will have to do the math once you know all your run lenghts. Keep in mind that you can always bump up to 100 or even 200 volts.

-Hal

Hal Bissinger/COMSYSTEC wrote on Tue, 26 October 2010 19:33

Keep in mind that you can always bump up to 100 or even 200 volts.

-Hal

Could you give me details on this? Can a 70v system be "modified" to be bumped up to 100 or 200v to account for cable loss, or is this something that has to be started from scratch?

The current plan is to have 2 runs (1 upstreet/ 1 downstreet) with each run having a max # of 30 speakers, each tapped at 30 watts.
Distances for each run are about 2500'
Each run is to be driven from a channel of a 2x 1200 watt amp (69v).
I've installed larger systems before, but not with runs this long.
I appreciate your help and comments.
Thanks,
BJ

Bradford "BJ" James wrote on Wed, 27 October 2010 08:32

Could you give me details on this? Can a 70v system be "modified" to be bumped up to 100 or 200v to account for cable loss, or is this something that has to be started from scratch?

The current plan is to have 2 runs (1 upstreet/ 1 downstreet) with each run having a max # of 30 speakers, each tapped at 30 watts.
Distances for each run are about 2500'
Each run is to be driven from a channel of a 2x 1200 watt amp (69v).
I've installed larger systems before, but not with runs this long.
I appreciate your help and comments.
Thanks,
BJ

100V is standard for use in many export markets so 70V fixed install products often already have a 100V tap.

I have seen installs run 3x 70V transformers together to make 210V output (Daytona racetrack to push audio several miles) , it seems you can make 200V easier by adding one extra output transformer to a unit with both low Z and 100V output taps. Just wire the extra transformer primary to low ohm tap, and 100V winding in series with the existing 100V output. (Note: this must be a true transformer, a cheaper auto-former will not work for this).

Warning, 200V will sting you pretty good when music is playing, so treat this like the 200V it is.

Also the speaker transformer taps will now be hot (2x voltage is 4x power) you may need to make sure you don't send a lot of low bass to the transformers at higher voltage.

JR

John Roberts {JR} wrote on Wed, 27 October 2010 09:12

Bradford "BJ" James wrote on Wed, 27 October 2010 08:32

Could you give me details on this? Can a 70v system be "modified" to be bumped up to 100 or 200v to account for cable loss, or is this something that has to be started from scratch?

The current plan is to have 2 runs (1 upstreet/ 1 downstreet) with each run having a max # of 30 speakers, each tapped at 30 watts.
Distances for each run are about 2500'
Each run is to be driven from a channel of a 2x 1200 watt amp (69v).
I've installed larger systems before, but not with runs this long.
I appreciate your help and comments.
Thanks,
BJ

100V is standard for use in many export markets so 70V fixed install products often already have a 100V tap.

I have seen installs run 3x 70V transformers together to make 210V output (Daytona racetrack to push audio several miles) , it seems you can make 200V easier by adding one extra output transformer to a unit with both low Z and 100V output taps. Just wire the extra transformer primary to low ohm tap, and 100V winding in series with the existing 100V output. (Note: this must be a true transformer, a cheaper auto-former will not work for this).

Warning, 200V will sting you pretty good when music is playing, so treat this like the 200V it is.

Also the speaker transformer taps will now be hot (2x voltage is 4x power) you may need to make sure you don't send a lot of low bass to the transformers at higher voltage.

JR

Hello,

More than likely you'd have no code inspectors breathing down your neck, but, in Michgan... any voltage over 100v is considered "High voltage" and is subject to a whole slew of code regulations.

Before you get started I'd suggest you investigate these Codes before you attempt any work.

Good Luck,
Hammer

Quote:

Hello,

More than likely you'd have no code inspectors breathing down your neck, but, in Michgan... any voltage over 100v is considered "High voltage" and is subject to a whole slew of code regulations.

Before you get started I'd suggest you investigate these Codes before you attempt any work.

Good Luck,
Hammer

Since this is out on the street hanging from poles and lamp posts the NEC doesn't apply. Further, I assume that the poles and lamp posts are municipally or privately owned the only permission you would need to get is from the owners. Of course you still need to observe height clearances over the streets and driveways, you don't want a truck to hook your cable taking everything down for blocks! Normally this is 18 feet. You also need to maintain proper clearance from other voltage carrying conductors (above, below or where you cross them), but if this is the only thing on the lamp posts this is not going to be an issue.

-Hal

Will 12g UTP suffice for this distance on a 70v system?

I don't think I'll venture into 200v territory for this as it'll probably be 10 or more years if ever, before they would ever need to expand. Good info to know though.
Thanks,
BJ

How many speakers and what are the distances between each of them and to the amp? Probably need to see a drawing here if there are taps or branches and not a straight run. Are we assuming 30W transformer taps on all speakers?

-Hal

Hal Bissinger/COMSYSTEC wrote on Wed, 27 October 2010 15:31

Quote:

Hello,

More than likely you'd have no code inspectors breathing down your neck, but, in Michgan... any voltage over 100v is considered "High voltage" and is subject to a whole slew of code regulations.

Before you get started I'd suggest you investigate these Codes before you attempt any work.

Good Luck,
Hammer

Since this is out on the street hanging from poles and lamp posts the NEC doesn't apply. Further, I assume that the poles and lamp posts are municipally or privately owned the only permission you would need to get is from the owners. Of course you still need to observe height clearances over the streets and driveways, you don't want a truck to hook your cable taking everything down for blocks! Normally this is 18 feet. You also need to maintain proper clearance from other voltage carrying conductors (above, below or where you cross them), but if this is the only thing on the lamp posts this is not going to be an issue.

-Hal

Hello Hal,

I never mentioned the NEC. That is not what I was referring to. In the State of Michigan anything over 100 volts needs to be installed by a State Licensed Electrician. I'm guessing that Bradford is not a State Licensed Electrician.

Also... We do not have (at this time) a specific code Licensing requirement for Low Voltage (less than 100 volts).

In regards to the height requirement of Cable crossing alleyways, walk paths, driveways and streets, I agree with the general requirement you've listed, but I'd suggest he further consult the Local Codes, as these do vary from Municipality to Municipality, here in Michigan.

There are other State and local requirements not mentioned here that would also apply to the stringing of cable, such as egress and ingress of a building, Fire stop, when conduit is needed, UV protection of cables, proper grounding of suspended wire & cable, etc...

Thank You,
Hammer

Hal Bissinger/COMSYSTEC wrote on Wed, 27 October 2010 22:46

How many speakers and what are the distances between each of them and to the amp? Probably need to see a drawing here if there are taps or branches and not a straight run. Are we assuming 30W transformer taps on all speakers?

-Hal

2 straight runs is what I have planned right now.

Run "A"- exits the building and goes about 200' before we hit the first lamp post. There will be 2 speakers mounted on the post, each tapped at 30watts. Then repeat 14 times about every 160'. Total run ~ 2500' `900watt load- off one side of a 2x 1200 amp- straight run.

Run "B" is pretty much the same but won't have the full run completed all at once. I do want the electrician to run the cable for the entire run though, so let's assume the same # of units and taps as run "A"

No branches are planned, which is why I would like to double check this with you. Perhaps I should spec 12g 2 or 3 pair for each run and split the load. My longest run will still be 2500', but less load on each run. Then parallel the runs at the amp. Cable starts to get real expensive and heavy though. If a single run of 12g would do it, that would be preferred.

A reputable electrical contractor will be installing the cable. Everything will be done to code and safety where applicable. All I need to do is provide proper spec's for the cable.

Bradford "BJ" James wrote on Thu, 28 October 2010 08:21

Hal Bissinger/COMSYSTEC wrote on Wed, 27 October 2010 22:46

How many speakers and what are the distances between each of them and to the amp? Probably need to see a drawing here if there are taps or branches and not a straight run. Are we assuming 30W transformer taps on all speakers?

-Hal

2 straight runs is what I have planned right now.

Run "A"- exits the building and goes about 200' before we hit the first lamp post. There will be 2 speakers mounted on the post, each tapped at 30watts. Then repeat 14 times about every 160'. Total run ~ 2500' `900watt load- off one side of a 2x 1200 amp- straight run.

Run "B" is pretty much the same but won't have the full run completed all at once. I do want the electrician to run the cable for the entire run though, so let's assume the same # of units and taps as run "A"

No branches are planned, which is why I would like to double check this with you. Perhaps I should spec 12g 2 or 3 pair for each run and split the load. My longest run will still be 2500', but less load on each run. Then parallel the runs at the amp. Cable starts to get real expensive and heavy though. If a single run of 12g would do it, that would be preferred.

A reputable electrical contractor will be installing the cable. Everything will be done to code and safety where applicable. All I need to do is provide proper spec's for the cable.

Hello Bradford.

200ft. to the first lamp post and about 160ft. to each subsequent lamp post?

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

Good Luck,

Hammer

I never mentioned the NEC. That is not what I was referring to. In the State of Michigan anything over 100 volts needs to be installed by a State Licensed Electrician. I'm guessing that Bradford is not a State Licensed Electrician.

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.

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

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

double post

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

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

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

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

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

Thanks JR. That helps.
Cheers.
BJ

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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => SR Forum Archives => Installed Sound/Contracting FUD Forum Archive => Topic started by: Bradford "BJ" James on September 08, 2010, 12:29:32 PM