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PA newbie - how to connect things up!

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PA newbie - how to connect things up!

Postby minstermineman » Wed Jan 08, 2020 4:32 pm

Hi all - new here as well as being new to anything involving sound systems and audio stuff.

I have been tasked with looking after a sound system used to play music from CD to small audiences during fireworks displays.
We are talking max 100 people (usually) - outdoors - and the system will be operated from one side of the audience.
With 2 pairs of speakers, each side of the audience at the front facing them.

The system comprises an amplifier, a mixer, and a cd player - all mounted into a flight case.

And the 4 speakers - 2 bass type and 2 others - no idea on specifications for them but they were supplied with the setup so I guess are suitable. They are marked EV on the fronts and each one has a SpeakOn 'IN' and 'OUT' connection - nothing else.

The CD player and mixer and amp are all connected and work - but I wish to know how I should be connecting up and using the speakers with it.

All cabling is 2.5mm with SpeakOn at each end.
My max cable length is 20 Metres.

The amp is a W Audio EPX120 https://prolight.co.uk/product/epx-1200-amplifier

I cant figure out how to add a picture of the rear of it but is in the link..

I have had it set up using its bridged connection and just running cable from the amp to one to speaker to another to another etc, which worked - but have since been told that this is bad and that I am likely to blow stuff up that shouldn't be.

I have also been using the 2 large rotary controls on the front set at about 1/3 - and again have been told I should be having these all the way up full and using the mixer to adjust volume.

Basically I am winging it and need to be told how to set it up, particularly with regards to setting up the 2 pairs of speakers. I went with the bridged option as it seemed the simplest - there is no need for concert quality during a firework display!

But I also need the setup to be simple so that other people apart from me can take it out and set it up with just an idiots guide to getting running.

I also have been very fastidious about keeping the flight case with the amp etc well covered up in as it is used in the rain very often - ie bin bags and whatever cover I can cobble together to keep the wet out.

How robust are speakers - I have been covering them in bin bags until just before use then uncovering them.

Sorry for the many probably daft questions!

Thanks

Gerry
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Re: PA newbie - how to connect things up!

Postby Sam Spoons » Wed Jan 08, 2020 4:53 pm

Hi Gerry and welcome.

EV is a brand of speaker, and a decent one at that. But without knowing the exact model it's difficult to advise how best to wire them up. But, playing safe, start by plugging the left/CH1 output from the amp into the left sub and linking that to the left top, then do the same for right/CH2. Switch OFF bridge mode and set the mixer up so that the playback it not going into the red on the meters. Turn the power amp's volumes up until the music is loud enough.

Ideally you'd want a 'crossover' and two amps* but, as you say, concert quality is not a requirement. The only other nag I can think of is how the mixer is connected to the amp, I'd use the main outputs, left to CH1 and right to CH2 so the sound is in stereo.

More info if possible including, maybe, pics of the connector plates on the speakers.

* It may be that the subs have a passive crossover built in but most likely not as the modern way is to use an active crossover before the power amp(s)

HTH
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Re: PA newbie - how to connect things up!

Postby Hugh Robjohns » Wed Jan 08, 2020 5:04 pm

minstermineman wrote:I have had it set up using its bridged connection and just running cable from the amp to one to speaker to another to another etc, which worked - but have since been told that this is bad and that I am likely to blow stuff up that shouldn't be.

Yes, I fear that that's quite likely!

Like many, the W Audio amplifier is actually two separate amplifiers in one box, intended for driving separate left and right stereo speaker systems. However, the two amps can be used together to make a single-channel (mono) amplifier by switching to 'bridge mode'... as you have.

However, whereas each amp channel working separately can cope with speaker loads down to 4 Ohms, when you select bridge mode the minimum load doubles to 8 Ohms. If you connect a speaker (or chain of speakers, in your case) with less than 8 Ohms you seriously risk destroying the amplifier or, if you're lucky, forcing it to shut itself off in a protection mode. Both are very embarrassing situations, but the first is also very expensive! :lol:

Now, we don't know what your speakers are yet, but most passive PA speakers present a nominal 8 Ohms load. If you connect two identical 8 Ohm loads in parallel -- which is the usual configuration for linking as you have -- the total load halves. So when connecting the top box in parallel with a subwoofer, the total load seen by the amp is just 4 Ohms.

So, if you chain all four eight-ohm speakers (two subs and two tops) together in parallel, the total load seen by the amplifier will be just 2 Ohms, and that will challenge most 'ordinary' amps, and will definitely over-stress your amp operating in bridge mode!

So.... DON'T USE BRIDGE MODE!

Instead, connect one amp channel to one sub, and then link one top to that sub only. Do the same for the other amp channel to feed the other sub and top. That way, each amp will be driving a four-Ohm load, and will be happy, with around 600Watts available to each pair.

You'll need to connect both the left and right main outputs from the desk to the left (channel 1) and right (channel 2) inputs of the amp, of course.

I have also been using the 2 large rotary controls on the front set at about 1/3 - and again have been told I should be having these all the way up full and using the mixer to adjust volume.

That's a more debateable point....

The good news is that your current settings imply you have plenty of gain on hand, so you should still find the system is more than loud enough when working as two separate channels instead of in bridge mode.

It is true that many PA operators will set the amp input attenuators flat out (fully up), and control levels with the master output fader at the desk, and I suspect that will work fine for you too.... but some experimentation might be needed.

The issue is that in situations where the system is running fairly quietly -- with the master fader more than, say, 10dB down, there is a (small) noise penalty to working that way with the amp attenuators flat out.

So in that case it would be a better idea to keep the desk's output fader near its reference level, and turn the amp input attenuators down a bit instead until your system is working at the kind of (reduced) level you need.

How robust are speakers - I have been covering them in bin bags until just before use then uncovering them.

Without knowing what the speakers actually are, it's impossible to say how weather-proof they are. There should be identifying model labels on the back somewhere. If you can take a look and let us know that would be helpful! But using bin bags is obviously a wise precaution... and you may well find that, actually, you can leave them in place with very little reduction in sound level or quality for the show to guard against any unexpected rain.

Sorry for the many probably daft questions!

If you don't know the answer, the question isn't daft! :thumbup:

There are lots of decent books on live sound, but one of the most approachable is our own, available from all good book retailers: Image

And welcome to the SOS forums!
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Re: PA newbie - how to connect things up!

Postby minstermineman » Wed Jan 08, 2020 5:30 pm

Thanks guys for the welcome and also the prompt replies!

I will see about getting the speaker specifications tomorrow and post them up here.

I looked up the mixer and it is this one - most probably overkill for our use - but better to have the capability than be stuck one day I guess.

https://www.behringer.com/Categories/Behringer/Mixers/Rackmount/RX1202FX/p/P0486#googtrans(en|en)

Its next outing is for a small display on Friday - so Friday morning I will have to have a play and make sure I can get sound without using the Bridge connector but using the Channel 1 and 2 connectors instead.

So my cable run should be something like

Amp Channel 1 > speaker 1 > speaker 2

(and the same from Channel 2 going to the other side of the site.)

Is there a maximum cable length at all?

I have to ask - if Bridge mode is bad - why is it there?

Gerry
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Re: PA newbie - how to connect things up!

Postby Hugh Robjohns » Wed Jan 08, 2020 6:05 pm

minstermineman wrote:So my cable run should be something like...

For completeness:

Mixer Left > Amp Channel 1 > Sub speaker 1 > top speaker 1

and

Mixer Right > Amp Channel 2 > Sub speaker 2 > top speaker 2

Is there a maximum cable length at all?

The issue with long cables is that they absorb some power and reduce the amplifier's control of the speaker. The chunkier the cable, the smaller that effect will be, and you're currently using fairly reasonable 2.5mm2 cable which should be good up to 20-30 metres. If you needed more than that I'd switch to 4mm2 cables for the long run between amp and subwoofer. The (hopefully as short as practical) cable between the sub and top box could remain 2.5mm2).

I have to ask - if Bridge mode is bad - why is it there?

It's not bad, it's just that you have to be mindful of the load you want it to drive. It's provided because it's a very convenient way of combining the output power of two amps to drive power-hungry loads -- typically big subwoofers -- while maintaining compatible and interchangable power amps in the rack to give some redundancy in case of failure.

If your speakers happened to be 32 Ohms per cabinet (which is very unlikely!) you could chain them together and power them with that amp in bridge mode quite safely because four 32 Ohm parallel cabinets would present an 8 Ohm total load.

But in your situation, that particular amp just isn't designed to power four standard 8 Ohm cabinets daisy-chained in parallel. It wouldn't be happy with four 16 Ohm cabinets daisy-chained in parallel either, as the total load would be 4 Ohms... and the minimum it can work with in bridge mode is 8 Ohms.

There are also alternative ways of wiring speaker combinations in series and parallel combinations to derive an appropriate load resistance... but that all gets a bit complicated and confusing and won't be relevant to your situation.
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Re: PA newbie - how to connect things up!

Postby minstermineman » Wed Jan 08, 2020 6:27 pm

Great - thanks Hugh,

I get the cable thickness argument - its a resistance thing we also have to watch out for when firing displays electronically. 'Thicker' is better for longer runs - just weighs a lot more!

Complicated wiring sounds bad - the simpler the better - we also need to be mindful that our cable runs are likely to be on rough ground and have to get from one side of an audience to the other, - so the least number of cables actually on the ground the better.

Just running one across the front to the furthest pair of speakers then a short lead between the 2 sounds good to me, as this is what we do (did) with the daisy chaining.

Gerry
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Re: PA newbie - how to connect things up!

Postby Hugh Robjohns » Wed Jan 08, 2020 6:37 pm

minstermineman wrote:Just running one across the front to the furthest pair of speakers then a short lead between the 2 sounds good to me, as this is what we do (did) with the daisy chaining.

The cables would need to be arranged something like this, with long cables from the amp to the subwoofer on each side, and then a short cable from each of those to their accompanying top boxes:

Speaker wiring.png
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Re: PA newbie - how to connect things up!

Postby minstermineman » Thu Jan 09, 2020 4:09 pm

Not entirely sure this will work but here goes - a few pictures showing whats what, and further down a few questions in keeping with my topic title!

Our speakers - 2 of each type

Image

Image

Image

The entire setup bar the speakers...

Image

Now - there are left and right channel controls on the amp - the way it is all connected up now only the left control on the amp works and the 2 far left sets of sliders work.
This is the same whether speakers are connected to Ch1 or Ch2.

The right amp knob does nothing.

Now I was thinking I should be having one controlling Ch1 and one controlling Ch2 speakers - so obviously There is something I have not done in my ignorance with setting things up.

So here is how it all looks at present.

If you spot anything I have set up wrongly or needs altering please let me know!

CD connection to mixer..

Image

Mixer connection to Amp..

Image

Back of Amp + settings..

Image

I wont be there to play with it until tomorrow morning - and it is out on a show tomorrow night - so I may need to use it as originally if I need more leads or anything!

If it does need any more specifics would be great !

Before any budding electrical types shout at me - I am at home making up speaker cables and also redoing that Power cable which is hanging in there by a thread ....

Thanks

Gerry

Edited some urls to make the pictures play nicely!
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Re: PA newbie - how to connect things up!

Postby Kwackman » Thu Jan 09, 2020 4:45 pm

minstermineman wrote:The right amp knob does nothing.

One thing I noticed..
On your mixer, the pan pot on Ch.2 (fed by CD "R" output?) should be panned to the right. In your photo it's panned to the left.
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Re: PA newbie - how to connect things up!

Postby Hugh Robjohns » Thu Jan 09, 2020 5:26 pm

minstermineman wrote:... a few pictures showing whats what...

Perfect. Thanks.

So we're looking at a a pair of SX300 12" passive full-range speakers (300W), and a pair of SB122 12" passive subwoofers (400W) with integral low-pass filtering. Excellent.

...the way it is all connected up now only the left control on the amp works and the 2 far left sets of sliders work. This is the same whether speakers are connected to Ch1 or Ch2. The right amp knob does nothing.

That's odd. :problem:

The Ch1 control on the amp will be the only one that works if the amp is switched to Bridge or Parallel mode (slide switch at the back) , but it looks like it's in Stereo mode, so both input controls should be working, each controlling their own pair of speakers.

CD connection to mixer..

Ah... I see the problem. The connections are fine. The issue is on the mixer set up.

You'll see the (bottom black) pan knobs for inputs one and two are both panned hard left, so both channels of the CD player are coming out of the mixer's left output and there's nothing from the right output.

In fact all the pan and balance knobs across the whole mixer are set to route everything to just the channel 1 (left) output.

If you want the music in stereo, turn channel 2's pan control fully clockwise (leaving channel 1's fully anticlockwise). That will route the left channel from the CD to the left pair of speakers via amp channel 1, and the right CD channel to the right speakers via amp channel 2. Problem solved!

Alternatively, if you want the music in mono (which is often preferred in PA setups where the speakers are far apart), turn both pan controls to the middle, so both CD channels feed both outputs equally.

I wont be there to play with it until tomorrow morning - and it is out on a show tomorrow night - so I may need to use it as originally if I need more leads or anything!

No new leads needed. Three seconds worth of knob twiddling is all that's required...

Before any budding electrical types shout at me - I am at home making up speaker cables and also redoing that Power cable which is hanging in there by a thread ....

Very glad to hear it! :lol:

Hope that helps.

H
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Re: PA newbie - how to connect things up!

Postby minstermineman » Thu Jan 09, 2020 7:27 pm

Kwackman wrote:
minstermineman wrote:The right amp knob does nothing.

One thing I noticed..
On your mixer, the pan pot on Ch.2 (fed by CD "R" output?) should be panned to the right. In your photo it's panned to the left.

Well spotted - I had absolutely no idea what a pan pot was though !

Fortunately with Hughs mention of the Black knob being all the way to the left it all became clear.

Good to hear it is something simple and no more cables or connecting should be needed.

I'll admit to not knowing the function of those little Black knobs - which - when I was using the setup feeding from the Red bridge connection and daisy chaining the speakers, I just used to put vertically upright - (along with all the others in fact !)

The only knob in those columns that I used to adjust, being the top one - adjusting it up or down until the clipping led went off.

Can you tell my sound guy career is lacking in basic knowledge :lol:

I figured out how to get a cd to play - and how to get the cue button to start it at 00:00 by using the time button and wheel (top right) and I pretty much left it at that.

I set the mixer channel sliders to their [ ] position and then used the 'master' volume on the right to set the sound volume overall.

The amp knobs I have always set at around the 1/3rd / 10 'o' clock position, unless it showed the clipping led - when I turned it down.

I now posses 3 x 20m 2 x 10m and 2 x 4m 2.5mm speaker cables with real Neutrik connectors, having changed some el cheapo ones that were damaged.

And a power cord with insulation that goes all the way into the plug... which I may yet change to a Neutrik branded one.
Does anyone know if these come in 90 degree bend varieties? as then the case covers would fit over this without having to plug in and unplug it every time.

Gerry
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Re: PA newbie - how to connect things up!

Postby Hugh Robjohns » Thu Jan 09, 2020 7:54 pm

minstermineman wrote:I'll admit to not knowing the function of those little Black knobs

The mixer manual will probably explain it, but basically you have a single (mono) input channel that you need to route to two outputs (left and right). The pan pot determines how much of the input channels signal is routed to each output. In its middle (12 o'clock) position it sends the channel equally to both outputs, and if you're sat midway between the two speakers the sound will appear to come from the middle too.

If you turn the pan pot anti-clockwise, towards the left, it will send more signal to the left output and less to the right, and the sound image will appear to move closer to the left speaker as well. And vice versa if turned clockwise. A few minutes experimentation will make it all very obvious. The balance knob does much the same thing for stereo inputs.

You might find this article of help: https://www.soundonsound.com/techniques ... cal-mixing

Does anyone know if these come in 90 degree bend varieties?

It's a Neutrik Powercon. Ive never seen a 90 degree elbow version I'm afraid...
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Re: PA newbie - how to connect things up!

Postby Sam Spoons » Thu Jan 09, 2020 7:55 pm

Probably not a great idea to put the covers on while it's running anyway as it will affect the power amp's cooling.
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Re: PA newbie - how to connect things up!

Postby minstermineman » Thu Jan 09, 2020 9:35 pm

Sam Spoons wrote:Probably not a great idea to put the covers on while it's running anyway as it will affect the power amp's cooling.
Indeed Sam, I probably wasn't too clear when I posted that - but it was more for when I pack things away, just unplug its extension and tuck the power lead inside.

Gerry
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Re: PA newbie - how to connect things up!

Postby Sam Spoons » Thu Jan 09, 2020 10:00 pm

That is certainly a time saver, and you are less likely to do what I did on a gig in Anglesey a few years ago and leave the one and only power con cable back in Manchester :blush:
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Re: PA newbie - how to connect things up!

Postby MarkPAman » Fri Jan 10, 2020 10:14 am

I've managed to leave a slightly unusual power cable in a dark field somewhere in Dorset, which lead to something of a panic at the next day's gig. :thumbdown: :oops:

I now have the replacement cable tied into the rack. Still have to unplug to get the lid on, but at least I always know where it is.

I now keep a spare connector in the van in case I ever need to make another too!
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Re: PA newbie - how to connect things up!

Postby Sam Spoons » Fri Jan 10, 2020 11:50 am

That is my tactic, I tried tying the cable to the sub's handle but it looked a bit vulnerable so now I have a couple in the cables tub and another in the mic box. Haven't gone so far as to carry a spare connector too though.
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Re: PA newbie - how to connect things up!

Postby minstermineman » Sun Jan 12, 2020 12:04 pm

Just to follow up - took it out Friday for its first try in its new configuration as in Hughs diagram, and all worked just fine. :D

I did have to extend the cable from left to right by joining a 20m and 10m ( I bought a Neutrick coupler 'just in case' )

So I was thinking - is there a chart or site or online reference that can be used to work out maximum speaker cable lengths?

Input amp power - input cable length - input speaker details and get a max speaker lead before problems sort of thing?


Thanks to everyone who may have stopped me blowing up our system using dodgy connections - I could still manage it with our other stuff though!

Gerry
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Re: PA newbie - how to connect things up!

Postby Hugh Robjohns » Sun Jan 12, 2020 12:36 pm

As I said earlier, if you need to go more than 25-30metres I'd increase to 4.0mm cable....

But to be honest if you're working speakers at that kind of distance from the amp you'd actually be a lot better off either ditching the passive speakers and amp setup completely and going with a new active system, or get a second amp and run each speaker stack with it's own local amp, so that the long cable runs are power and line-level audio, not speaker-signals.

H
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