Speaker cable, what gauge of wire?

[PYROmaster]

Hey guys,

 

It's been a while since ive been on here but I need some help.

 

I am doing an event where I have to play sound on a train,

I have the speakers and amp/audio source sorted, but what is causing an issue is the speaker cable.

 

Now, it is not possible to have an amp in each carriage for power reasons, the power will be at one end of the train along with the control for the system.

 

So passive speakers it is, and I need the ability to seperate each carriage's audio.

 

At the moment there is 4 carriages but I would like to build in a bit of headroom to add more...

 

So a multicore speaker cable that runs down the outside of the train is needed,

 

Each carriage is 63ft long, so thats 250+ ft / 80m ...

 

Currently discussions are at the stage where its cost of such cable, and what is the difference between using 2.5mm cable or 4mm cable... (as there is a significant cost difference)

 

So, in summary, I am needing at least 8 core cable, 2.5mm or 4mm (or other)? Running a length of 80m ...

 

Aside: ive not tried but would linking the -ve of all 4 channels to one core allow me to increase channel count: ie- 8 core cable with 1 -ve and 7 +ve .. giving me 7 channels to play with?

 

Thanks guys.

Hope you can help.

[timsabre]

You need to tell us the power rating of the speakers / amp, it is impossible to answer the question otherwise.

 

But I don't really understand why you say "it is not possible to have an amp in each carriage for power reasons", if you are running cable for speakers you could run cable for power instead? Then you'd only need 2 core power running the length of the train, plus the signal cable for each carriage which will be cheaper than speaker cable.

 

Aside: ive not tried but would linking the -ve of all 4 channels to one core allow me to increase channel count: ie- 8 core cable with 1 -ve and 7 +ve .. giving me 7 channels to play with?

 

It depends on how the amp is designed. Some types of amp drive both the positive and negative side and would blow up if you did that. Also the common core would need to be 4x the size of the other cores, to maintain the power handling.

[richie1575]

Is constant voltage an option? To get clarity on a train, surely a large quantity of speakers producing relatively low spl's would be the order of the day!

Without knowing the nature of what you are doing, it's difficult to help, but for me, I'd look into 100v line!

[Jivemaster]

Having once done a gig on a preserved steam train, the source of power is the most critical feature, where will the train park and how far is that from the power supply?

 

How much power are you intending to use? Likely 2.5mm flex will be fine -just the far speakers will be quieter. A length of 100M does come into 100v line territory, is this a possible solution for you?

[cedd]

What's the duration of the event? Would battery powered PA's in each carriage and just sending line level not be an option?

Socapex has been used for loudspeakers in the past. That'd open up rental if you can just find appropriate fan in's and out's.

 

As others have suggested, I'd be starting to look at 100V line.

[adam2]

4 speakers per coach, each 4 ohm, connect all 4 in series so as to give 16 ohms impedance per coach.

 

Connect the 4 coaches in parallel which takes the impedance back to 4 ohms so as to suit a standard amplifier. Adding a fifth coach would take the impedance only a little below 4 ohms. Select wattage of speakers and amplifier according to sound level required.

 

Other points to consider include

 

Temporary or permanent ? if permanent remember plugs and sockets for when the train formation changes.

 

Source of power ? Diesel multiple units should have 24/28 volts DC from the engine for lighting, diesel locomotives may have 96/110 volts DC from the starting battery. Steam locomotives usually have no electricity supply. Buffet cars may have 230 volts AC from a modern generating set.

 

Do not attempt to use any board power without specific permission and a very clear understanding as to voltage, type of current, polarity, frequency if AC, and fuse sizes.

 

 

 

 

 

[DrV]

Note OP needs individual audio for each carriage so paralleling/100V won't be suitable.

[Brian]

Aside: ive not tried but would linking the -ve of all 4 channels to one core allow me to increase channel count: ie- 8 core cable with 1 -ve and 7 +ve .. giving me 7 channels to play with?

 

Not a good idea unless you know 100% that the amps have a common connection to the -ve output terminal. Many amps are now internally bridged with the -ve terminal bearing no resemblance to 'earth' or each other.

[GR1]

Power and control needs to be in the centre of the train. You need to tell the organiser this and not negotiate about it. Then you could use 2.5mm to the coach either side of control and 4mm to the next coaches. Given that you need to allow 25-30 metres per coach you should be OK for a third coach either side of centre. Beyond that length of train I would tell the organiser that they must provide power at another location to keep the speaker cable runs short enough.

[Owain]

I'm sure I've looked at this question before but I can't find where.

 

Anyway, 80 metres is quite short for 100V line, and your overall power requirement will be low so speaker impedance will be high compared to the wire - you could probably use 4-pair cat 5 data cable with each pair supplying 4 x 5watt speakers per coach.

 

Cat5 is typically 20 ohm per 100 metres round-trip, compared to 2000 ohm for a 5 watt speaker at 100V. So for 4 speakers your power loss in the cable would still be only 4%. And Cat5e is thin, very cheap, and can be crimped easily to connectors onsite without soldering. (Use the approriate plugs for solid or stranded core!).

 

I am assuming this is a stationary train on a preserved railway and will not be subject to an operating railway's Safety Case.

 

 

[TomHoward]

I'm slightly lost why the 8-core cable would need to run the length of the train - even if you've got the amps at one end, the cores for the first and second carriages don't need to run the rest of the length?

[dbuckley]

Adam gives a big hint here;' the trick is to have the speakers in series so that the cable impedence is dwarfed by the cable.

 

Problem is you then need big amplifiers to deliver the requisite power into 8R, 16R 32R whatever, even though the amps aren't running at anything like the load the front panel blinkenlitz would suggest. Its a trade-off: cable cost versus amp costs.

[Jivemaster]

The "best" solution depends on what content you are playing -disco to background music to docu commentary, and on the equipment you already have. Is the content intended to be the same in each zone, Are you going to do the gig often (can you amortise equipment over lots of gigs?).

 

When I did a wedding gig on a preserved steam train the crowd soon shuffled up and down the train to be near to or far from the disco, and being a steam train it was DIRTY -coal dust everywhere. Also when the train ride stopped for the disco they let the boiler go out so the heat went off in the carriages so it went COLD.

[sunray]

Why is everybody making this sound so complicated? First of all what is this being installed for?

[PYROmaster]

Phew! Busy week, only just had time to read your replies, I will try and supply a bit more info now....

You need to tell us the power rating of the speakers / amp, it is impossible to answer the question otherwise.

 

But I don't really understand why you say "it is not possible to have an amp in each carriage for power reasons", if you are running cable for speakers you could run cable for power instead? Then you'd only need 2 core power running the length of the train, plus the signal cable for each carriage which will be cheaper than speaker cable.

Specifics are speakers are 40-50W (ish) Achat 104 from Thomann (note: great quality for the price!) and the amp is Behringer NU4 6000 ... so each amp channel is more than capable of powering each coach

 

There is 8 speakers per coach - after a test last year 8 is optimum, with less the sound is patchy and more is just overkill really.

I have already had a discussion with the railway's Traction & Rolling Stock Director (who is also an electrical engineer) and I have been told categorically I cannot run power down the length of the train.

 

Having once done a gig on a preserved steam train, the source of power is the most critical feature, where will the train park and how far is that from the power supply?

 

How much power are you intending to use? Likely 2.5mm flex will be fine -just the far speakers will be quieter. A length of 100M does come into 100v line territory, is this a possible solution for you?

The train, when not in use will be parked in a platform which has suitable power connections to charge the batteries on the coaches

For power use, the above speakers and amp, plus mixer and PC for the audio source...

If its just quieter I can just turn up the furthest coach's amp channel ... ?

Im not sure on 100v line PA, is it suitable for a theatrical style event, audio quality is paramount!

 

 

What's the duration of the event? Would battery powered PA's in each carriage and just sending line level not be an option?

Socapex has been used for loudspeakers in the past. That'd open up rental if you can just find appropriate fan in's and out's.

 

The event is about 6 hours, give or take, from start to finish each night (4 'shows' each night), battery power is unfortunately not an option and I have looked into it the existing batteries on each coach only just sustain the coach lights for each night and would not cope with an amp too...

I did originally spec soca but as its a permanent solution would need to be purchased, and the Finance Director nearly fainted when he saw the price....

 

 

4 speakers per coach, each 4 ohm, connect all 4 in series so as to give 16 ohms impedance per coach.

 

Connect the 4 coaches in parallel which takes the impedance back to 4 ohms so as to suit a standard amplifier. Adding a fifth coach would take the impedance only a little below 4 ohms. Select wattage of speakers and amplifier according to sound level required.

 

Other points to consider include

 

Temporary or permanent ? if permanent remember plugs and sockets for when the train formation changes.

 

Source of power ? Diesel multiple units should have 24/28 volts DC from the engine for lighting, diesel locomotives may have 96/110 volts DC from the starting battery. Steam locomotives usually have no electricity supply. Buffet cars may have 230 volts AC from a modern generating set.

 

Do not attempt to use any board power without specific permission and a very clear understanding as to voltage, type of current, polarity, frequency if AC, and fuse sizes.

 

 

Thanks for the info, we came up with a wiring method that gave us 4ohms back at the amp on each channel (with 8 speakers per coach). :)

It is a permanent installation, and inter-coach connections are sorted

The coaching stock is 4x BR Mk2a coaches, with a steam loco at one end and a diesel shunter at the other, so I am on my own in terms of power source, which will be a small genny powering a 24v battery charger, which charges 2x 12v truck batteries, then I use an inverter to the PA system, this worked very well last year as it means if the genny goes out the batteries give enough time to finish a 'show' and then get it back on...

 

 

Power and control needs to be in the centre of the train. You need to tell the organiser this and not negotiate about it. Then you could use 2.5mm to the coach either side of control and 4mm to the next coaches. Given that you need to allow 25-30 metres per coach you should be OK for a third coach either side of centre. Beyond that length of train I would tell the organiser that they must provide power at another location to keep the speaker cable runs short enough.

In the current situation this is not possible, going forward maybe, but as it stands, no.

The main problem is where to put the generator....

 

I'm sure I've looked at this question before but I can't find where.

 

Anyway, 80 metres is quite short for 100V line, and your overall power requirement will be low so speaker impedance will be high compared to the wire - you could probably use 4-pair cat 5 data cable with each pair supplying 4 x 5watt speakers per coach.

 

Cat5 is typically 20 ohm per 100 metres round-trip, compared to 2000 ohm for a 5 watt speaker at 100V. So for 4 speakers your power loss in the cable would still be only 4%. And Cat5e is thin, very cheap, and can be crimped easily to connectors onsite without soldering. (Use the approriate plugs for solid or stranded core!).

 

I am assuming this is a stationary train on a preserved railway and will not be subject to an operating railway's Safety Case.

 

 

I did think of cat5, but being so thin it's not really suitable for powered amp signal ?? Line level, I wouldn't have batted an eye... (also, see above with regards to speaker watts and qty)

 

And, yeeeaaahhhh... the train is in motion for the show, the only time it stops is to pick up and drop off the audience.... it is a heritage railway and an SMS has been written specifically for the event.

 

 

I'm slightly lost why the 8-core cable would need to run the length of the train - even if you've got the amps at one end, the cores for the first and second carriages don't need to run the rest of the length?

This was done last year with 3 coaches, put in as a temp fix. as the train was assembled specifically to the event - however the installation needs to be permanent and not dictate what order the coaches end up in.

 

Why is everybody making this sound so complicated? First of all what is this being installed for?

... Sound on a train?

Major Christmas event, the core of the show on the train is the sound, so has to be right.

Although, as a heritage railway, it also needs to be flexible to cater for any other event - hence the ability to play something different in each coach...

 

 

I hope that has helped a bit...

What I have got from this is that 2.5mm will be ok for the current length, but much more and we will need a rethink - however there wont be any increase in length for some years (until there are longer platforms on a longer track).

In the past week I have also been told that there will be an 8 core down each side of the train, giving me 8 channels to use on 4 coaches (stereo feed - YAY!), so impedance will be brought down a lot, also giving a bit of redundancy should one amp channel go down sound should continue, not great but at least it is still there!

If anyone can shed light on if I can connect the -ve of each channel together with the behringer nu4 amp, that would be great, I would use 2 wires for that, giving me 6 channels for 6 coaches...

 

Thanks for the replies.