System Building

Putting Your Own PA System Together

Building a sound system - either in a fixed installation or for touring - is often a highly personal process, from deciding what to get, to assembling and using it.

The main objectives, however, are generally less personal. A PA system has to fulfil two main purposes:

A touring system is also likely to encounter variations in venue-size and layout, and may also require flexibility in monitor capacity or other areas. For this it will help if some degree of modularity is incorporated in the design: maintain at least brand-consistency in key components like amplifiers and loudspeakers, so that adding or interchanging them is straightforward and has no significant effect on level - you don't want one amplifier to require different gain or controller settings from others - or on tone.

Having decided on what to get, there are a few points that will make life on the road much easier.

  1. Flight-case everything. One big box on wheels is a lot less bother to move about than lots of little boxes you have to carry one or two at a time, and it is easier to keep track of one box than five. However, allow for the fact that you may sometimes need to lift it, and try not to make any box with its contents too heavy for a few men to handle safely.

    A flight-cased amplifier or effects unit will last indefinitely, and will look like new when it is ten years old. Carry it loose and it will be missing a couple of knobs, sporting a couple of scratches, and looking ten years old before it is out of warranty. Wrapping it in a blanket won't give it enough protection, but will still take time and trouble every time you do it.

    Consider buying or making dedicated cases for things like microphones. If you have a foamed case with ten microphone-shaped cut-outs you can see at a glance whether there are ten microphones in it (if you carry them loose, or in some other way, you have to count them every time you want to know if they are all there). Also, you will notice instantly if one is missing, and anyone thinking of stealing one will know that. Nothing is foolproof, thief-proof or tamper-proof, but don't make it harder than necessary to keep an eye on things.

  2. Label everything. Anyone finding or using it might need to know
    1. What it is (or, if it is a container, what is in it). If you need to find it, it is much quicker and easier to read what is on the lid than to open every box.
    2. Which way is up. Opening a rack-drawer full of spare bits and pieces the wrong way up will take longer to sort out than it would have taken to stencil a couple of arrows on the box.
    3. Where it needs to be. Local crew will often help with loading in (although loading out is often another story). If it says STAGE on it in large letters, they won't need to ask you where to put it, and with a bit of luck they will take it to the right place.

      Cables require special attention. Usually (but not inevitably) you can tell what a cable is meant for by the type of connectors on the ends of it. However, it is less easy to tell at a glance...

    4. How long it is. One common convention is to use coloured markers to show how long it is. While there is no universal standard, another common convention is to use standard resistor colour codes (Black = 0, Brown = 1, Red = 2, Orange = 3, Yellow = 4, Green = 5, Blue = 6, Violet = 7, Grey = 8, White = 9). A 5-metre cable might as well have green markers on it as any other colour. Other than for specific jobs on a fixed installation, cable-length does not need to be exact, so you don't need microphone cables of every imaginable length: a couple of different lengths will generally cater for most jobs. For stage use, 5m and 10m lengths are useful (although each can be a bit on the short side for some jobs, so you might want to go for 6m and 12m cables instead). You can chain XLR cables if a single cable isn't long enough for the distance it has to cover, but if you expect to be working in arena-sized venues you may need 20m cables as well.
    5. Which one it is. There might be 20 or more cables converging at the stage-box end of the multicore. Plugging something into the wrong channel is easily done, but if both ends of each cable have a unique identifier (numbering cables is one simple option) it is easily checked and put right. Otherwise, tracing the wire all the way across stage is at best time-consuming.
    6. Where the one you want is. If all your microphone cables - regardless of length - are in a big pile, it may take some time to find a short one. One useful thing about XLR connectors is that they can be chained together, so a handy way to store them is on a reel. If you number them as well - and put them on the reel in number-order - you don't have to count them to know they are all there. When you want a 5m cable, you just take one off the end of the 5m reel. This method also reduces twisting and kinking, so your cables will last longer.
    7. Who it belongs to. It is much less likely to ‘walk’ if it is obvious whose it is, and will stand some chance of finding its way back to you if it is mislaid or left behind.

    Connector panels (see below) also need to be clearly marked. OK, you can generally make an intelligent guess as to which input is which, but if there is a label (e.g. Monitor One) then you know, and - more to the point - so does the local helper with the IQ of a root vegetable.

    Colour coding can be helpful here, as well. For example, several mixer manufacturers use yellow for master faders and red for group/auxiliary faders. If all your monitor leads, cases and connectors are red, and all the front-of-house ones are yellow, plugging it all up is much easier to make sense of for any willing but untrained helpers. As a coincidence, Red = 2 and Yellow = 4, so if your front-of-house speaker system is on four-core cable and the monitors are on two-core that would work too!

    For things that never change, relatively permanent labels are best (a label printer is useful, and transparent heatshrink will make sure cables stay labelled). For things that change from show to show, tour plates or tags and a marker pen are in order. If the same flightcase - an amplifier-rack for example - always has the same contents it can be useful to stencil the weight on the box as well.

  3. Be consistent. Use the same colour and numbering schemes throughout, and use the same name for the same thing everywhere you refer to it (don't call it ‘Monitor A’ on the multicore and ‘Wedge 1’ on the amp-rack).

    Although there are few absolutely universal wiring conventions (apart from mains electricity: if you don't know mains wiring conventions, LEAVE IT ALONE), the following are common defaults:

    1. XLR. Pin 1 = Ground/Screen, Pin 2 = Signal +/Hot, Pin 3 = Signal −/Cold.
    2. TRS (Tip Ring Sleeve, balanced) Jack. Tip = Signal +/Hot, Ring = Signal −/Cold, Sleeve = Ground/Screen.
    3. TRS (Tip Ring Sleeve, insert) Jack. Tip = Send, Ring = Return, Sleeve = Ground/Screen.
    4. Loudspeaker connectors. Pin 1/Odd = Signal−/Cold, Pin 2/Even = Signal+/Hot. Generally, lowest numbered pair = lowest frequency speakers, higher numbered pairs = higher frequency speakers (in ascending order in all cases).

    If you use cables with non-standard wiring (e.g. ground-lifted, polarity-reversed, or pad connections), make sure these can be easily distinguished from other cables. If the difference is at one end of the cable (e.g. pin 1 is disconnected at one end only), make that easy to see from the label too.

  4. Organise your equipment and cabling. If a compressor can stay more-or-less permanently in the same rack connected to the same insert loom, put it there and wire it in. If you have 10 processors in your rack, connect them all to a single IEC mains distribution unit (or if you have to have 13A plugs, screw or Velcro a couple of 6-way 13A boards into the back of the rack). The less plugging and unplugging you have to do, the easier it is to set up and put away, and the longer your cables, connectors and equipment will last. If cables are always used in a group (inserts and sends/returns in your effects racks are an obvious candidate for this), either group them by taping them together, or make up a dedicated loom. Plastic cable ties can keep cables in the back of a rack tidy, but if you need to re-patch more often than once in a blue moon it may be easier to use Velcro ties, or even leave them loose.

    Amplifiers and controllers generally live together, so can be patched together in the same flightcase. It also makes life easier if you make up patch-panels to bring the plug-in points to the front of the rack, rather than grovelling about in the back of it every time you connect or disconnect an input or speaker lead.

    Generally, avoid having to scrabble around in the back of equipment racks at an event to connect or disconnect anything, which means wherever possible either:

    1. Use patch-panels so that cables can be connected or disconnected at the front, like the amp-rack mentioned above.
    2. Use looms so that mixer inserts, for example, only need to be connected on-site at the mixer's insert points (the other end of the cable is permanently connected to the processor in the rack).
  5. Only use professional connectors. Although other good quality brands exist, we only use Neutrik connectors on our signal and speaker cables, and some of our oldest cables are still in perfect working condition after over 20 years of regular use. Modern electronic equipment is very reliable, and most system faults come down to faulty interconnections. Cable and connector problems do not always stop there: shorted outputs can burn out transistors (on line-level as well as power amplifier outputs). Shorted input wires can put 48V phantom power across an expensive microphone coil. Ultra low-budget connectors are a false economy. Even if they don't do any other damage, in five years you'll spend more on replacing them than you would if you had used decent ones in the first place.

    The same applies to cable. For touring use, the main things to look for are flexibility (go for rubber cable that coils easily), good conductors (OFC - Oxygen-Free Copper - is pretty much universal), and plenty of conductor area (at least 2.5mm core) for loudspeaker cable. Don't use unbalanced cable even for unbalanced leads, and use balanced leads and components wherever possible.

  6. Test everything before you take it on the road. If the whole system or any part of it doesn't work in your workshop (...lock-up, garden shed, living room...), it isn't going to work when you get to the venue. Use a cable tester (if you don't have one already, buy one before you do anything else), and check every new cable, whether you have bought it or made it yourself. Check signal inputs and outputs on every channel of every new piece of equipment, and if you are wiring it into a rack, check it again after you have wired it in. Never assume that because it is new it is in working order. If you think testing things is a bit of a pain, wait until you have to fault-find five minutes after the show should have started.

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