Riggy
Senior Member
I need to install underground cabling for a public address system at an Autograss track. Is it as simple as running 1.5mm2 2C SWA? I guess the longest run will be 100m.
Public Address Cabling
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what sort of PA system?
will there be transformers at every horn?
will there be transformers at every horn?
Riggy
Senior Member
I guess I need more info!
Here's what I know so far:
It's a 12Vdc system running from batteries.
Each "speaker" (probably not the correct term, horn?) is connected back to base using 2 cores.
The current system is tied to fences, etc. and is therefore vulnerable to damage.
Here's what I know so far:
It's a 12Vdc system running from batteries.
Each "speaker" (probably not the correct term, horn?) is connected back to base using 2 cores.
The current system is tied to fences, etc. and is therefore vulnerable to damage.
With these type of jobs , slightly off our usual scale if you like, I tend to take expert advice TBH.
Basic 2 core SWA may well be fine , I wouldn't know , a cheaper screened cable may do the job .
Basic 2 core SWA may well be fine , I wouldn't know , a cheaper screened cable may do the job .
Hi
How big is an Autograss track? Is the current system definitely loud enough etc? Are they using 100V lines and Transformers at each Horn speaker? If so then replacing current
with thick (same total CSA). SWA sounds OK over short distances. For small 100V systems there is a guide here http://www.thatcable.com/info/100v-Line-Public-Address-PA
(Note the 100V I'm talking about is the AC voltage of the audio sent down the line to a step down transformer at each speaker. I assume the 12V you mention means they run the amps off a car/ battery (Different thing))
If it is an 8 ohm non-transformer speaker system and not 100V you need very thick or multicore cable . . .
If they are hoping it will 'improve the sound' etc then a proper design + beefier system and proper approach will be needed:
The last time I was an expert on this it was for University 'House' systems in Bars and discos so I've no idea at all what regs might need to be met in a public stadium but for indoor sound systems in large student bars and discos etc we used thick multicore cabling with no CPC but half the cores as + and the other cores as - Again you need to ask them to specify what they need.
HTH
How big is an Autograss track? Is the current system definitely loud enough etc? Are they using 100V lines and Transformers at each Horn speaker? If so then replacing current
with thick (same total CSA). SWA sounds OK over short distances. For small 100V systems there is a guide here http://www.thatcable.com/info/100v-Line-Public-Address-PA
(Note the 100V I'm talking about is the AC voltage of the audio sent down the line to a step down transformer at each speaker. I assume the 12V you mention means they run the amps off a car/ battery (Different thing))
If it is an 8 ohm non-transformer speaker system and not 100V you need very thick or multicore cable . . .
If they are hoping it will 'improve the sound' etc then a proper design + beefier system and proper approach will be needed:
The last time I was an expert on this it was for University 'House' systems in Bars and discos so I've no idea at all what regs might need to be met in a public stadium but for indoor sound systems in large student bars and discos etc we used thick multicore cabling with no CPC but half the cores as + and the other cores as - Again you need to ask them to specify what they need.
HTH
Manator
©Honorary Essex Boy™
I was about to say the same thing, most PA speaker configs we did were 100v systems wich were looped, dc would require a more consideration.
All our station tannoy systems are 100v systems with transformers at speaker end. we have the speaker systems wired in 1.5mm twin cable.
We are upgrading the old George henry systems, for a new system using cat6 for the microphone/ptt & alarm button links.......................so much easier than the old 2x 6 core cables.....happy days.
We are upgrading the old George henry systems, for a new system using cat6 for the microphone/ptt & alarm button links.......................so much easier than the old 2x 6 core cables.....happy days.
Riggy
Senior Member
Wow!
Fantastic, thanks very much.
I'll investigate what's currently there, now I know what to look for.
Further note.
for 100V line systems, any flexible cable needs to be reinforced insulation.......like this
http://www.rs100.co.uk/Sound-System-Accessories/Cable_and_Leads/100V_Line_2_Core_Shielded_Speaker_Cable
I can recommend this lot - bought a good load of kit for a few jobs......aftersales is excellent, too
for 100V line systems, any flexible cable needs to be reinforced insulation.......like this
http://www.rs100.co.uk/Sound-System-Accessories/Cable_and_Leads/100V_Line_2_Core_Shielded_Speaker_Cable
I can recommend this lot - bought a good load of kit for a few jobs......aftersales is excellent, too
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Way back in my younger days with a previous employer..
factory & office PA systems were one of the services we did...
they were 100v line system with line matching transformers either built in or adjacent to each speaker..
the speakers were cabinet type ones in the offices and metal horns 8W or
re-entrant horns.. (a sort of long horn but double backed folded in on itself to make it more compact..)
In those days the cable we used was 0.85mm twin cable (No earth)
some of the cable runs were well over 100m...
sprawling out in a radial formation around the factory..
Some of these were foundry's and meal press drop forge stamping machines..
Bl00dy noisey..
Probably noisier than a grass track...
I would hazard a guess that twin 1.5mm SWA would be up to the job...
REMEMBER
the 100v is a peak voltage when the particular amplified audio hit a high...
it is not a standing voltage that is sitting on the cable 100% of the time!
opcorn
factory & office PA systems were one of the services we did...
they were 100v line system with line matching transformers either built in or adjacent to each speaker..
the speakers were cabinet type ones in the offices and metal horns 8W or
re-entrant horns.. (a sort of long horn but double backed folded in on itself to make it more compact..)
In those days the cable we used was 0.85mm twin cable (No earth)
some of the cable runs were well over 100m...
sprawling out in a radial formation around the factory..
Some of these were foundry's and meal press drop forge stamping machines..
Bl00dy noisey..
Probably noisier than a grass track...
I would hazard a guess that twin 1.5mm SWA would be up to the job...
REMEMBER
the 100v is a peak voltage when the particular amplified audio hit a high...
it is not a standing voltage that is sitting on the cable 100% of the time!
opcorn
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You can put the output of almost any amplifier onto a 100v line by using the transformers used at the speaker end the opposite way round at the amplifier end!
http://www.maplin.co.uk/100v-line-matching-transformer-454494
http://www.maplin.co.uk/100v-line-matching-transformer-454494
But then you lose the benefit of the Tx AND delay would you not,?
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???
presume referring to mic delay to prevent feedback howling??
I was just confirming the concept that any amplifier output can be transformed up them back down again...
background music from and audio source no problem...
Open mic in range of a speaker...
can cause issues if no delays built in!
But if mic not in range of speaker then no probs!
We had some systems connected to internal factory phone systems...
Dial a number..
put out a PA call from anywhere in the factory..
Some recorded call then output when handset was put down...
Others (cheaper version) just went live to speaker while phone still off hook..
caused a few feedback loops where foreman's office phone was sitting below a horn speaker!!!!!!!!!
.
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Funnily enough I did start to write a long(er) post including how modern practice is to install many speakers in several groups each at equal distance from the original sound source and feed each group from an amp that has the sound delayed and equalised such that the original sound would arrive at a particular speaker (or listener) group at the right moment to reinforce (not preceed/confuse) the original sound or that of other nearby speakers. This technique is one of the reasons you can sometimes tell which train is leaving from which platform these days. (BTW Our ears get baffled by PreEcho but have evolved to take post-echo for granted)
In which case you might run 100V line 1 from the rack to the first speaker or group of speakers, 100V line 2 to the next furthest away etc. The delays also tend to stop howl round too even in echo prone places like stations and conference halls.. . .
However this is starting to become a fairly complex system, need installing and setting up by PA specialists and as OP said cables were run in star fashion to each speaker (singular) and the system ran off a 12V supply I started to think I was on the way to suggesting a helicopter when all that was needed was a shopping trolley
In which case you might run 100V line 1 from the rack to the first speaker or group of speakers, 100V line 2 to the next furthest away etc. The delays also tend to stop howl round too even in echo prone places like stations and conference halls.. . .
However this is starting to become a fairly complex system, need installing and setting up by PA specialists and as OP said cables were run in star fashion to each speaker (singular) and the system ran off a 12V supply I started to think I was on the way to suggesting a helicopter when all that was needed was a shopping trolley
