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east electronics 19th March 2013 08:16 PM

here is an interesting project
the project is to install rental sound across a road 1 klm long with real speakers no 100v horns or so, preferably 2way 15" monitors powered at about 200W continuously for one day for a street party .

Local authorities will provide power at any desirable point at the road and also provide a lift truck with the crew for one morning for the wiring ( to take place above people's head some 8 meters high on the traffic lights or the street lights )

the fee for the rental cannot exceed 1600 euros ...

In my company plenty of 15" 2way speakers exist , some others active , plenty of amplifiers and so on

Question is about distribution of signal taken as a fact that the source is in the beginning of the road ...

Obviously 1klm speaker cable ( s) is out of the question eventhough might exist in my company still this is not possible

Balanced line is an option but still maybe 1klm of XLR cables exist in my shop but i presume that using pieces of 20-30-40 m installed on the air is very bad practice since if any of these plugs is faulty you will eventually loose part of the system .

Installing new fresh cable and plugs might also be an option but 1klm of balanced cable +plugs +installation will obviously exceed the rental fee which is limited to 1600 euros plus VAT

Then again if one supposes that 1klm might come as outsourcing rental in a lower price than new this will include a couple of problems

--One that i am not aware of any balanced output that is able to drive 1 klm cable plus 10-20 amplifiers on it ...Use of a distributor that exist in my company could be an option only if signal source was somewhere in the middle but this will also require more than 1klm of balanced cables

--Second is that in my fleet as said there is plenty of 15" 2Way speakers with amplifiers but not enough for the all project I need to add many of my active speakers to complete the line .That will include the problem that most of my amplifiers feature a ground lift switch while none of my active speakers does ..That will produce a hell of a ground loop an d noise since this will be powered from about 10 different spots across the road ...

Any ideas on how to do that ?

The limit is the fee and the budget

Some ideas for wireless distribution of signal through FM wifi or LAN was on the table but still this will require products that do not normally exist in small rental company so obviously the cost to get them will eliminate any profit since the budget is so low ...

Kind regards \

Enzo 19th March 2013 11:19 PM

Common wireless microphone systems do not have that range. But an FM receiver at each speaker, and a low power FM transmitter at the signal source ought to work. SHow buisiness uses wireless communication in many ways, companies like Clearcom make a wide range of products.

Clear-Com: Partyline, Digital Matrix, IP and Wireless Intercoms

Some of your speakers may not have a ground lift, but it is simple enough to wire up a short cable with the ground open, to insert at the end of the long cable before plugging into the speaker. I always carried a couple 6 inch long ground lift XLR cables in my kit just to solve such problems.

It would not take much power for an FM transmitter to reach 1km. I don't know what the laws are about radio spectrum use where you are, but I am sure it would be easy to find out.

counter culture 20th March 2013 02:13 AM

It's unlikely that you can use FM, the power required is almost certainly more than the permitted unlicensed power. You need a link budget with >99% uptime.

You could use FM on a coax, but 1km of coax will probably exceed the budget, not to speak of connectors, etc., etc.

Even using wireless FM I don't think it is possible to meet the requirement within the budget.

You could try and get the help of a local radio station.

Make an estimate of the number of speaker stations required, calculate a reasonable cost that will include a profit including installation and tear-down labour, but excluding a distribution system. This will give you something to explain to the client the problems and costs involved and give you a baseline to think about what kind of budget you need to allow for the link alone.

east electronics 20th March 2013 06:43 AM

ok this is turning bad ...

Fm laws will not allow cant be on the illegal side
Fm reception equipment and transmitter do not exist in my company Getting them or rent them will probably increase the cost and leave no profit
Even if coax can make it still i need to get FM receivers with ability to drive an amplifier at almost 1 volt output times 10 at least
Local radio station doesn't exist in the area we are to close to Athens so only big radio stations that will not fall for that ...

as about the budget when the costumer is the Greek Government its very unlikely that you will find anyone to explain what you have to say ..

There is got to be another way ...

gmphadte 20th March 2013 09:01 AM

You can feed FM to a FM booster like the cable guys do and use small cheap $1-2 receivers at each speaker.

Gajanan Phadte

east electronics 20th March 2013 11:05 AM


Originally Posted by gmphadte (
You can feed FM to a FM booster like the cable guys do and use small cheap $1-2 receivers at each speaker.

Gajanan Phadte

not really since i need at least 1V of real output to drive active speaker or amplifier but as said first its illegal and obviously you cannot eliminate the fact that in a town like Athens with so many FM broadcasting stations the chance that interference with some other station will eventually occur.

One option could be to tune the all system out of the 88-108 FM band but generally this idea includes way too many variables to be plug 'n play

gmphadte 20th March 2013 11:40 AM

You have to feed the FM using a cable to all the speakers, not wireless. Then boost the audio to 1 volt using some cheapo chipamp.

Gajanan Phadte

east electronics 20th March 2013 11:47 AM

hmmm no too many to construct and get ... too many variables

There is got to be other way to do it more safe

Kind regards

JMFahey 20th March 2013 12:54 PM

Short answer:
you *can* drive , say, 40 amps (1 every 25 meters) along a 1Km balanced line, with acceptable loss (worst case 30% voltage loss at the end) and good frequency response, so don't worry about that .
Trust good old copper cable, don't get into RF problems.
You need a line driver (or a good mixer) capable to drive 2 or 3 V RMS into a 200 ohms load, nothing more.
Worst case, you build a small booster, I can suggest one.
Cost?: 12 100M rolls of bulk balanced cable and 80 XLR connectors plus setup expenses (food/personnel salaries/etc.)
Try to get the Government/Political party/Church/whoever runs the show to supply transport and people to help.
You won't lose money, will earn little if any, main advantage in such events is goodwill from interested parties, may be useful in the future, your choice.
*Who* set that Job price?
It's quite tight, bordering on unrealistic.
It's a *big* job, literally; that price might be more reasonable if it was inside some Stadium or at a City park, within 100 meters.
It's up to you to decide on this .... or .... are you sort of forced to do it?

east electronics 20th March 2013 01:28 PM

2 Attachment(s)
well the job is already done the only reason i placed the post is to see if other people will think alike .

As you all very well know Greece is under economical crises so there is plenty of these type of jobs which actually was carnival style street party and yes you get plenty of Mayor people or city hall bureaucrats that will release the specs with 1600 euro +vat budget take it or leave it .

So as a specialist it was a good challenge to make profit out of a job that other people didnt know how to or want to take

The additional cost in parts was 162 euros totally and the job was done in 2 days while in the first on of my personnel installed one cable and the second where 5 people installed about 40 speakers starting 6.30 in the morning and get the job done by 9.30 .

1000m of the most inexpensive telephone cable was about 100 euros and then 12 of the devices shown down under provided the signal . the packs cost 62 euros totally grand total 162 euro including VAT

The device originates from car stereo and its a : SPEAKER TO LINE LEVEL ISOLATED ADAPTER
it has a couple of resistors wired as a divider to attenuate speaker level signal to something lower , +one 47mfd capacitor to eliminate any DC ,+one isolation transformer 1:1 at 150Ohms , and on the other side in the output of the transformer a trimmer to match teh output to a desired level according to the needs of the various amplifiers or active speakers used .

Obviously the transformer eliminated any possibility of ground loop or noise ....

I could as well used classic DI boxes but those was working in an other gig the same day

Now the all line was driven by a hifi amplifier rated 2X60W while some 2X20W was more than enough to drive the packs and the 1klm line .

Sound was superb ,absolutely noise free and dead quiet
For your pleasure here is pictures of the speaker to line adapter plus a schematic of the internals so we all get the picture better

Happy profitable regards

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