here is an interesting project

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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 \
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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.
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.
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 ...
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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
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?
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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Forgot to mention that in the output of these devices we installed one amplifier and 4 speakers on it covering a distance with speaker cables then of about 100 m

When we run out of speakers in the output of the device we drive 4 active speakers and after we went with balanced cables in to out and so on

Mixing the system resolved the cable issue since part of the system was done with speakon while the rest was made with balanced so my company didnt run out of cables ( other gigs was going on at the same time )

Kind regards
Dear Sakis, as you see I hit the nail right in the head, both with the amount of powered speakers (which you had not stated), the distribution system, the driving with a power amp (I fact the boosterI suggested was a bridged TDA2030, which both provided balanced output and could drive down to 8 ohms), etc.
Only we used balanced cable and part of the profit was keeping 40 30 meter balanced cables.
You wonder how I was so sure?
Ahem!!, look at a couple of my jobs ;)
Any similarity between Argentina and Greece is *not* a coincidence.
Including both being Mediterraneans and having a *long* history of economic crisis:
In the first one you see one "head" of the Carnival street, with added line array systems on both sides of the stage.
There sits the Province Governor, the Mayor and Press, plus the Judges who choose the most beautiful girls.


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Simple method

Use one amp with 100 volts output and one 100 volt speaker at the end to load the amp.

Now, use one stepdown transformer for each active speaker for deriving audio of 1 volts. You may find that the signal is dropping as the distance increases. So use 100:1 transfomer for the nearer ones and use 110/3vct for the further ones. Use a pot/resistors to set the input level to the actives.

Gajanan Phadte
Or someting between a line-driver and a 100V amp:
Use an ordinary small stereo amp and drive on echannel inverted. That way you will be able to drive a long cheap speaker cable which you use to feed your active speakers (maybe using resistive voltage dividers). Small series resistors at the output help keeping the amp stable with the capacitive loading of the long line. Maybe soem termination at the end would be good as well.
If there is any chance that you get this job several time I would also build a smal IC amp as line driver.



P.S: This job would be quite a bit of work for the amount of money you will get !
I put your query to an engineer friend of mine (Doug Ford and he came up with a similar method. His reply follows.

"1/ Use cat5 cable to reticulate the signal.
Cost = AU$57/305m (WES components 'economy' CAT5).
Parallel the twisted pairs at the source, and at each drop-point, to reduce series resistance (although capacitance will rise).

2/ Drive the cable with a cheap, second-hand stereo amplifier connected for bridge-mode.
I'm sure they'd have an old 20+20 amp hanging around somewhere.
They may need to connect (say) a 2.7-ohm resistor between the amp outputs and the cable, to assure amp stability.
Distribution signal levels of around +20dBV (10Vrms) should easily be attained, with plenty of headroom.
If you want, terminate the cable with 120 Ohms at the far end (will increase cable attenuation, but will also give better stability & flatter response).

3/ Use screw terminal blocks at each drop-point.
These can be weatherproofed with an inverted cut down plastic milk or drink bottle.

4/ At each weatherproofed drop-point, connect a small 240V:24V transformer.
These cost about AU$8 each.
When used as an audio transformer, these have quite acceptable frequency response.
The 10:1 stepdown ratio, combined with (nominal) +20dBV line transmission levels, will provide a clean 0dBV signal at each drop-point.
The powered speakers should handle this level quite nicely.

5/ Variations in amplitude along the cable due to cable resistance are easily accommodated by the volume knobs on the powered speakers.

6/ Total cost (AU$):
Drive amp = Zero cost
Cable = 4 x $57 = $228 (1200m)
Screw connectors = 20 x AU$1.00 = $20.00
Transformers = 20 x AU$8.00 = $160.00 (if purchased new!)
Waterproof housings = Zero cost
TOTAL = AU$408 = 250 euro (approx)."
well done .... i ve done the exact same thing using actually single cheaper telephone cable but better audio grade transformer / circuit

The grate fun in this story was that since the set up was in a public place and a a lot of people was there obviously some of them belonged to the competition and they come over actually for industrial spying ....all of them wondered how i managed and all of them wondered ( and asked my people there ) about the ""magic boxes "" ....You see stereo items are not really known to PA people ...

Kind regards
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