# 70v PA system with Ski Timing cable



## zhenry (Sep 10, 2014)

Hi guys,

I've got a rather unique problem I could use some advice on. I do timing and wiring for a ski hill, and we are trying to put a PA system for music and voice on our race venue. As time and budget are tight, we would really like to be able to use the existing timing cable on hill.

It is a 25 pair, 24 guage direct burial telephone cable, CAT3 I would imagine. We use 9 of the pairs for timing signals, which are simple open/closed circuit impulses. The other pair is used to carry start to finish headset communication powered by a 9v speech amplifier. My question is, would running a 70v audio signal through one of the unused pairs cause bleed complications? I'm a little more worried about bleed into the headset communication pair at this point, although interference with the timing signal is a major concern as well.

Any advice would be greatly appreciated.

Thanks!
Zach


----------



## Vintage Sounds (Oct 23, 2009)

24 ga wire is nowhere near sufficient for any speaker purposes, especially not a PA. it will not carry the current required and you'll have extreme voltage drop, which in this case is going to manifest as signal loss. I suggest proper wiring.


----------



## Wpgshocker (Jan 25, 2013)

zhenry said:


> Hi guys, I've got a rather unique problem I could use some advice on. I do timing and wiring for a ski hill, and we are trying to put a PA system for music and voice on our race venue. As time and budget are tight, we would really like to be able to use the existing timing cable on hill. It is a 25 pair, 24 guage direct burial telephone cable, CAT3 I would imagine. We use 9 of the pairs for timing signals, which are simple open/closed circuit impulses. The other pair is used to carry start to finish headset communication powered by a 9v speech amplifier. My question is, would running a 70v audio signal through one of the unused pairs cause bleed complications? I'm a little more worried about bleed into the headset communication pair at this point, although interference with the timing signal is a major concern as well. Any advice would be greatly appreciated. Thanks! Zach


You could convert the output from the main amp to a balanced signal and send that down to another amp quite easily. 
Noise shouldn't be too much on an issue. If you are finding a crazy amount of noise, you could always convert to digital and sent that down the line, then back to analog. 

Unless I am misunderstanding and you want to splice into that 25pair several times down the hill to add speakers. Then no way.


----------



## zhenry (Sep 10, 2014)

Vintage Sounds said:


> 24 ga wire is nowhere near sufficient for any speaker purposes, especially not a PA. it will not carry the current required and you'll have extreme voltage drop, which in this case is going to manifest as signal loss. I suggest proper wiring.


What I am talking about is a 70v constant voltage system which is extremely low current and frequently run over telephone lines. The voltage is stepped up at the amp and each speaker has a step down transformer, allowing a single amp to power multiple daisy chained speakers.

My original plan was to send line level audio through a pair in the line and use powered speakers at each location, but my audio vendor tells me no one makes powered speakers that will perform in very cold temperatures and as far as I can tell he's right.

My main question is whether a 70v low current signal will bleed into the other pairs in a cat 3 cable.


----------



## FullDuplex (May 18, 2013)

zhenry said:


> My question is, would running a 70v audio signal through one of the unused pairs cause bleed complications? I'm a little more worried about bleed into the headset communication pair at this point,


It will almost certainly bleed thru to some extent, but maybe not enough to be an issue. This is sufficiently unusual that you probably need to try it to find out for certain. If you don't have the 70 v amp yet, can you borrow one? Just make a basic hookup with the amp at the bottom end maybe one speaker at the top, with its tap set at the lowest level - and blast it with music.


----------



## zhenry (Sep 10, 2014)

FullDuplex said:


> It will almost certainly bleed thru to some extent, but maybe not enough to be an issue. This is sufficiently unusual that you probably need to try it to find out for certain. If you don't have the 70 v amp yet, can you borrow one? Just make a basic hookup with the amp at the bottom end maybe one speaker at the top, with its tap set at the lowest level - and blast it with music.



The audio vendor will send out a tech with amps and speakers for $500 but not for 2 weeks. If we ended up buying from them they would credit it towards our order. This looks like it may be the way to go. I'd love to be able to run a separate wire but with the length of the course (around 2 miles) and our budget constraints I'm not sure we'll be able to do it this year.

I really appreciate everyone's help!


----------



## 8V71 (Dec 23, 2011)

Even with a 70 volt system there will be too much loss with 24 gauge wire. 50% signal loss at around 1500'.

ETA: It sounds like you have extra pairs which you could parallel together. If you have enough to equal 16 gauge that would get you almost 10,000' at 50% loss. Like FD said, you would need to try it out to see if this will effect your other signals too much. There will be a much greater chance of it working if your other signals are balanced as well.


----------



## zhenry (Sep 10, 2014)

8V71 said:


> Even with a 70 volt system there will be too much loss with 24 gauge wire. 50% signal loss at around 1500'.
> 
> ETA: It sounds like you have extra pairs which you could parallel together. If you have enough to equal 16 gauge that would get you almost 10,000' at 50% loss. Like FD said, you would need to try it out to see if this will effect your other signals too much. There will be a much greater chance of it working if your other signals are balanced as well.


I was able to speak with another resort today that installed a system similar to the one I described, and it sounds like they had nothing but trouble with their timing and are having to take it out.

Does anyone know about the performance of powered speakers and amps in extremely cold temperatures? We have 120v power all over the hill so that could be another way to go, but it's looking like we may just need to bite the bullet and start laying cable in phases as budget allows


----------



## guest (Feb 21, 2009)

zhenry said:


> What I am talking about is a 70v constant voltage system *which is extremely low current and frequently run over telephone lines. *


Wrong and not always. 

First off, using simple math, the current in a 70v system can still reach several amperes depending the the total wattage of the connected speakers. Easily well over what a 24ga wire can handle, plus you STILL have to factor in for voltage drop...you could easily have the speakers at the amp end driving at ear-bleed level and have barely a whisper from the ones at the end. 

Second, "frequently run over telephone lines" is the sign of a hack install. Yes, the 70 system allows for smaller conductors in a given installation, but using telephone lines results in wasted power heating up the wire. As in point #1, simple electrical laws make it so. 

The 70v system's MAIN purpose is to make it very easy to drive several speakers off of one amplifier without worrying about impedance matching (to stay within a 4 or 8 ohm amplifier rating), you only need not exceed the amps' total POWER capability. (For example, a 400w RMS at 4 ohm amplifier, with the proper 70 drive transformer connected to it, can safely power up to 400 watts of connected speakers, in any combination. You could drive 400 1-watt speakers, 800 half-watt, speakers, 200 2-watt speakers, etc.) All speakers are connected in parallel, very easy. To try that in a standard system would result in a nightmare combination of series and parallel connections to maintain a 4-ohm minimum rating. 




zhenry said:


> The voltage is stepped up at the amp and each speaker has a step down transformer, allowing a single amp to power multiple daisy chained speakers.


Correct.



zhenry said:


> My main question is whether a 70v low current signal will bleed into the other pairs in a cat 3 cable.


Absolutely it will and as I mentioned above it will not be low current.


----------



## guest (Feb 21, 2009)

zhenry said:


> I was able to speak with another resort today that installed a system similar to the one I described, and it sounds like they had nothing but trouble with their timing and are having to take it out.
> 
> Does anyone know about the performance of powered speakers and amps in extremely cold temperatures? We have 120v power all over the hill so that could be another way to go, but it's looking like we may just need to bite the bullet and start laying cable in phases as budget allows


Not surprised at all with what happened to that other resort. 

Contact QSC professional Audio http://qsc.com/ as they have a wide variety of rugged products and may have a solution...they also make 70v driver transformers and the ISA and CX series of amplifiers are available in 70v output models. 

As for the temp cable, you can use some #10 and #12 SO type cables to your speakers....start the run nearest the amp with the #10 and about halfway you can go to the #12 for the remainer of the run without too much loss. 

As for horns, economical and good sounding, use these: http://www.mcmelectronics.com/product/555-6565


Some more advice: Install an equalizer (or use a mixer with built-in EQ) and kill EVERYTHING below100hz and above 12khz on the EQ, leave all other bands flat. This will save amp power (a LOT) and protect your speakers as the horns will NOT reproduce anything under 100hz or above 12khz.


----------



## Wpgshocker (Jan 25, 2013)

http://www.visiplex.com/products/public_address_speakers.html

Wireless?


----------



## zhenry (Sep 10, 2014)

mxslick said:


> As for horns, economical and good sounding, use these: http://www.mcmelectronics.com/product/555-6565
> 
> 
> Some more advice: Install an equalizer (or use a mixer with built-in EQ) and kill EVERYTHING below100hz and above 12khz on the EQ, leave all other bands flat. This will save amp power (a LOT) and protect your speakers as the horns will NOT reproduce anything under 100hz or above 12khz.


Wow, those are cheap horns. I assume those are for voice only? We are trying to do music as well and our vendor recommended some Community speakers that came in at about $300 apiece.

He's also recommending a 16 ga 3 pair snake cable so 3 amps could power 3 zones, but that sounds like a lot of money in amps and cables to me. I like the idea of stepping the wire size down farther uphill.

The wireless stuff is interesting, I'll have to take a closer look at that. In the past we haven't had great luck with wireless signals on hill, due to distance, hills, obstructions etc. I'll look at those closer when I get home


----------



## guest (Feb 21, 2009)

zhenry said:


> Wow, those are cheap horns. *I assume those are for voice only? We are trying to do music as well *and our vendor recommended some Community speakers that came in at about $300 apiece.
> 
> He's also recommending a *16 ga 3 pair snake cable so 3 amps could power 3 zones, but that sounds like a lot of money in amps and cables to me.* I like the idea of stepping the wire size down farther uphill.
> 
> The wireless stuff is interesting, I'll have to take a closer look at that.* In the past we haven't had great luck with wireless signals on hill, due to distance, hills, obstructions etc.* I'll look at those closer when I get home


Those horns will do ok with music...they will of course have no low bass response at all...trust me, you do NOT want to try to do any low bass over such a large area. (Unless you have REALLY deep pockets.) 

For example, at Anaheim Stadium, for the Supercross races, they bring in subs and amplification to add bass and supplement the in-house P.A...they used over 2 dozen bass bins with 4 to10 18" drivers in them, and well over 150,000 watts (no that's not a misprint) of amplification..for the SUBS alone!! And remember this is an "enclosed" space. In the great outdoors the audio power requirements go up by a factor of three or more for a given size area. 

Horns will also hold up better under the severe conditions of a ski slope..subs and other conventional "coned" drivers WILL fail due to the cold. (Most will survive a day or so outdoors and in use, but only if stored whenever they are not in use, and that's a lot of labor.) 

*How big of an area are you trying to cover with the sound? That will determine the quantity of horns (and the tap settings and the total amplifier power) you will need. *For even coverage, it is far better to do a larger number of horns to spread the sound out rather than have a few horns that make people's ears bleed when next to them, but the folks 200 yards away can't hear crap. 

*And will this be a permanent installation, i.e. cables and horns/speakers stay up year-round, will it be a seasonal one, or one where cables and speakers are set up only when events are taking place? *

Can you post a model number or link to the speakers they quoted? That price sounds really high to me...depending on what exactly they are talking about. 

In general, most PA gear is severely overpriced for what it is and what it does. There are often less expensive and more reliable solutions available, but your vendor needs to think outside the box and have a variety of manufacturers to choose from. It is often a lot cheaper to get a separate amplifier and mixing board than to get an all-in-one P.A. amp with built in mixer. (Most of which would not have nearly enough power for your application.) 

16ga cable will *not* be big enough to cover the distances involved. You will be wasting power in cable losses. The three zones, in theory, wouldn't be a bad idea but really isn't necessary. (Unless for whatever reason you want to be able to play different "programming" in each zone.) 

Also standard snake cable will not hold up for long under exposure to the weather. Some snake cable will even easily crack when handled when the temps approach freezing. 

As for wireless, I caution you away from that. You have already had past bad experiences with it, and that will not magically go away with any of the systems you can get on a budget. Even the highest dollar systems can STILL fail to perform, and to get the signal out to all the speakers you'd need a transmitter with such high power that now you'll be looking at having to get an FCC license. (major hassle and expensive.) Many wireless mics can't even perform well anymore, they are severely power limited by FCC rules..a true pro wireless mic system is well over a grand now....and they still won't promise performance beyond 100-200 yards. 

I may be able to give you more detailed answers, but need to know the answers to the questions I bolded in this reply.

Meanwhile, check out the thread I started for more guidelines and info on 70v systems: http://www.electriciantalk.com/f10/70v-distributed-line-pa-systems-facts-myths-tips-72371/

I will be adding more to it over time as other questions or idears pop up.


----------



## zhenry (Sep 10, 2014)

mxslick said:


> *How big of an area are you trying to cover with the sound? That will determine the quantity of horns (and the tap settings and the total amplifier power) you will need. *
> 
> *And will this be a permanent installation, i.e. cables and horns/speakers stay up year-round, will it be a seasonal one, or one where cables and speakers are set up only when events are taking place? *


Thank you so much for all the information, that's really helpful and really useful, and sorry I wasn't able to get back to it over the weekend.

We aren't really aiming to cover the whole course at all, just about 8 areas where people typically stand. Being generous, people would only be standing in about a 200' radius around each speaker station. My plan was to put two speakers in each location.

The speakers our audio guy suggested were Community R15 and R25s, with the R15s being slightly cheaper. He though 2 speakers running at 60w in each location would probably be enough.

This would ideally be a permanent installation. The cable will definitely not be going anywhere once we lay it down but we could take down the speakers when the season ends easily enough.

I appreciate the advice on the wire. I really can't foresee any situation where we'd need different programming in different locations on the hill. How many conductors would you use? Would it be foolish to not run extras? I imagine snake wire is very expensive anyways.

Thanks again for all your input

EDIT: some more info from looking over my notes from the audio vendor

He suggested a 1000w amp, priced at $1500, and a digital signal processing unit at $500. 

At some point I'd also like to look into tying our system into the existing PA at the base lodge, so we could take over the whole area on event days.


----------



## guest (Feb 21, 2009)

zhenry said:


> Thank you so much for all the information, that's really helpful and really useful, and sorry I wasn't able to get back to it over the weekend.
> 
> We aren't really aiming to cover the whole course at all, just about 8 areas where people typically stand. Being generous, people would only be standing in about a 200' radius around each speaker station. My plan was to put two speakers in each location. I would do four of the horns I recommended to you set up in two pairs. Two horns/speakers will give you hot spots of sound.
> 
> ...


See the points I addressed above.


----------



## Mshea (Jan 17, 2011)

I used to own an ALGE S4 and an ALGE Timy. Both could carry audio over top of the timing impulses and use a 2 wire carrier. This was not 70 volts but simple intercom over 5 volts and we could clearly speak over the 2KM of wire between the base station and the start gate. I was timing cycling events.
A couple of points. Optical isolators are very important to protect your gear from impressed or induced voltages caused by lightning or even the potential difference between the top of the mountain and the bottom. This proves the wire is big enough for an intercom signal but definitely not big enough wire to drive the speakers too. You need an amplifier with its own power at each speaker location. Only signal should be on the telco pairs.. you can also parallel another pair for signal losses but again do not try and power remote speakers from the music source or you might find several pairs of useless wire in your telephone cable.

It has been a few years but if memory serves I think you are good for about 2000" on a single pair of 24 gage wire. adding another pair in parallel increases the signal distance


----------

