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General Chat Thread, PA System in General; I'm trying to design a PA system for our school hall that makes use of 4 speakers around the hall. ...
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    localzuk's Avatar
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    PA System

    I'm trying to design a PA system for our school hall that makes use of 4 speakers around the hall.

    Now, as the only real experience of sound systems has involved only 2 speakers, or speakers that link to each other, I've only had to deal with systems with 1 output.

    Can someone point me in the right direction for doing this? How can I connect up 4 speakers to a system? Do I need 2 power amps? how do I link them to the mixer, which only has one set of outputs?

    Any clues would be much appreciated.

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    richard.thomas's Avatar
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    You can get amps that have four outputs, front L & R and rear.
    It's also possible with most amps to have two speakers running off one channel so that you can have the two on the left going through the left channel and right going through the right.

    If you want to go down the two amps route you'll need to look into getting a crossover which will split the signal it gets from the mixer to the correct speakers. In a professional environment it'd split the high end, mid and low and send to amps for those speakers. I don't think you'll need to go down this route as it's going more towards the professional route.

    It depends on what you want to put through the speakers. I presume it's just music for assembles and possibly CDs for dances. If this is the case then getting a four channel amp is prob the best. If you have DVDs you could go abit wild and get a proper AV amp that has a surround sound decoder in it

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    localzuk's Avatar
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    Can you point me in the direction of a 4 output amp? I'd been looking at the Yamaha P3500S amps.

    What we need is a system that is unbreakable by kids... So I'm avoiding mixer amps.

    Also, if I were to go down the crossover route, would this idea work if I wanted to use the same range on each speaker (ie. there is no differentiation between top, mid and low in the speakers)?

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    localzuk's Avatar
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    Scratch that, Yamaha seem to make the XM4080 and the XM4180 which have 4 channels of output. I'll investigate these.

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    richard.thomas's Avatar
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    Quote Originally Posted by localzuk View Post
    Scratch that, Yamaha seem to make the XM4080 and the XM4180 which have 4 channels of output. I'll investigate these.
    Magic!


    And yes you can have a crossover that will just send all signals to two amps. But it's a waste of money really as you're just basically doing something that could be done without the use a crossover.

    It might also be worth looking into bridging amps. I forgot to mention this in the last post. That could also solve your problem!

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    maniac's Avatar
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    It's worth noting you can quite happily connect 4 speakers to a 2 channel amp, as long as the resistance of the speakers falls within the range for the amplifier.

    e.g if the amplifier is designed to work at 8ohms, you can connect 2 suitably rated 16ohm speakers in parallel to each channel which will give an 8ohm load to the amplifier and work absolutely fine with no damage to the speakers or amplifier. You can also connect 2 4ohm speakers in series, but you tend to suffer a loss in power output with speakers in series.

    This is a good guide, and explains all the technicalities to do with power amplifiers, including all about resistances!

    Power Amplifier: Buying Guide

    Mike

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    localzuk's Avatar
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    I've had a look at that but it would mean that the impedance would be reduced down to 2 ohms per channel, which is advised against by most amps. The XM4180 does the trick for me as the speakers (JBL Control 1 Pro) are 4 ohm. Nice and easy to do

    All this is due to my boss now wanting a sound reinforcement system instead of a simple PA.

    Thanks for the help everyone.

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    Andrew_C's Avatar
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    You need help from someone who knows what they are doing. All the talk of crossovers above is wrong, and if you implement a system with multiple sources all you will achieve, without careful design, is a muddy sound.

    Distributed speakers CAN work, but you need to consider any delays needed, and comb-filtering. If you are stuck with the 1s, then they can be run in series on a two channel amp (giving 8 Ohm impedance not resistance)

    Much better to move up from the Control 1s (which I like) to something a bit more suitable for your hall. The Control 1 was designed as a monitor speaker, but has found favour for PA in smallish rooms. It REALLY isn't up to this job.

    Trying to do reinforcement with speakers behind the audience will be horrid. The trick is to boost the sound that the kids make without the audience realising that you are doing it, impossible with the speakers behind the punters.

    So, a bit more detail (hall size, layout and budget etc) and we'll see where we go from there...

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    localzuk's Avatar
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    Well the system as it stands is quite simple - 4 JBL Control 5's. 2 at the front, 2 in the middle of the hall - all facing the same way - towards the middle/back. (Based on the design by a company that specialises in these systems). The hall is actually quite small (about 10m by 20m).

    I've settled on a simple system involving the XM4180 and the speakers above. No speakers would be facing forward, as I already know how bad that is for audio (my old high school did that, it was awful).

    To be honest, I don't even think our hall needs such a system, but my boss wants it, so who am I to argue? Layout wise, it is almost exactly the same as what the hall had in it the system before last, which was ripped out in favour of having some giant PA speakers at the front.

    So I'm quite happy with the design now.

    Put it this way - the system I have come up with is almost identical to a proposed one by another company, except with higher quality components. They were proposing to use Behringer (or however you spell it) components and no-brand, 30W speakers!

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    Andrew_C's Avatar
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    OK, in that case what you really need to be able to do is run the pair remote from the stage at a lower level than the front pair. It may be worth delaying them too. Ideally the sound from the stage should arrive at the listener just before the sound from the local speaker. Delaying may not be necessary, but at 10m you are looking at 20ms approx. The cheapest way may well be to buy a Behringer speaker management controller (don't knock it, there are few better at ANY price!) Not only would this give you the delays you need, but limiting as well (stop the kids blowing them off the walls). Additionally you can configure it to crossover for subs at a later date.

    Just to clarify, in one post you say Control 1, but now Control 5? The latter will be fine...

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    localzuk's Avatar
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    Quote Originally Posted by Andrew_C View Post
    OK, in that case what you really need to be able to do is run the pair remote from the stage at a lower level than the front pair. It may be worth delaying them too. Ideally the sound from the stage should arrive at the listener just before the sound from the local speaker. Delaying may not be necessary, but at 10m you are looking at 20ms approx. The cheapest way may well be to buy a Behringer speaker management controller (don't knock it, there are few better at ANY price!) Not only would this give you the delays you need, but limiting as well (stop the kids blowing them off the walls). Additionally you can configure it to crossover for subs at a later date.

    Just to clarify, in one post you say Control 1, but now Control 5? The latter will be fine...
    Thanks, I'll take a look. Only 144 from Studio spares. I may add it on to the order.

    And I've settled on Control 5's. The control 1's are just too feeble.
    Last edited by localzuk; 1st July 2008 at 12:32 PM.

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    Quote Originally Posted by Andrew_C View Post
    You need help from someone who knows what they are doing. All the talk of crossovers above is wrong, and if you implement a system with multiple sources all you will achieve, without careful design, is a muddy sound.

    Distributed speakers CAN work, but you need to consider any delays needed, and comb-filtering. If you are stuck with the 1s, then they can be run in series on a two channel amp (giving 8 Ohm impedance not resistance)

    Much better to move up from the Control 1s (which I like) to something a bit more suitable for your hall. The Control 1 was designed as a monitor speaker, but has found favour for PA in smallish rooms. It REALLY isn't up to this job.

    Trying to do reinforcement with speakers behind the audience will be horrid. The trick is to boost the sound that the kids make without the audience realising that you are doing it, impossible with the speakers behind the punters.

    So, a bit more detail (hall size, layout and budget etc) and we'll see where we go from there...
    Agreed.

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