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  Getting Started -
  Assembling a System

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This section is primarily aimed at people new to PA systems, who need a basic understanding of how to assemble a PA system from its various parts.

Contents


The main parts of a PA system

There are five main parts to any PA system:

  1. Microphones, DI boxes and other sources
  2. A mixer
  3. Power amplifiers
  4. Speakers
  5. An arrangement of cables to interconnect the equipment

The place of each of these parts in a simple system is illustrated below. (More complex systems may include additional components such as radio microphone systems, graphic equalisers, active crossovers, dynamics processors and outboard effects, as illustrated later on this page.)

Component parts of a simple PA system

With the exception of the cabling, these five main parts each have their own descriptions elsewhere on this website (follow the links in the list above), so on this page we will concentrate on how the parts are interconnected to create a complete system. Once connected, the audio signals will follow the path indicated by the white arrows in the illustration; this path is called the 'signal chain'.

In some systems, some or all of the power amplifiers are internal to the mixer or are internal to the speakers:

  • A mixer that includes power amplification facilities is called a powered mixer or a mixer-amplifier. This arrangement restricts the distance that is possible between the mixer and the speakers, because of the need to keep speaker cables as short as possible. Additional separate power amplifiers are often needed, except in the very smallest systems.
  • Speakers that include power amplification facilities are called powered (or active) speakers. Some systems use a mixture of powered and passive speakers, e.g. powered monitors and passive front-of-house speakers (or vice versa).

For further details on amplifiers and speakers see the Amplifiers and Speakers page.

If you have not already obtained your equipment, or you are looking to replace it or extend it, you might find these links useful:


Remote mixer arrangements

Systems in which an analogue mixer is located remotely from the stage usually employ a multi-core cable to provide for signal interconnections between the stage and the mixer location. This is usually referred to as the 'multicore' (or 'snake'). At one end, the multicore has a box called a 'stagebox'; this end is located (surprise!) on the stage. At its other end, the multicore has a suitable means (described in a later section) for its connection to the mixer.

When a digital mixer is employed, it is now common to replace the multicore with a digital interconnection, typically provided by one or more CAT 5e cables often referred to as a 'digital snake'. These cables usually connect directly to the mixer. This arrangement has the advantage of using much cheaper, thinner and lighter-weight cables between the mixer and stage, and also eliminating some sources of possible interference. In systems using this method, an equipment rack at the stage provides the 'stagebox' function, and additionally incorporates remotely adjustable microphone pre-amplifiers and analogue to digital and digital to analogue convertors.

Connection of microphones and instruments to the multicore

The illustration below shows a typical arrangement for a simple system using a multicore. Where a digital snake is employed, an equipment rack at the stage provides the stagebox function.

A system using a multicore

Smaller arrangements in which the mixer is located on-stage generally do not use a multicore, so for such arrangements this section can be taken to describe the connection of microphones and instruments direct to the mixer.

Assuming that you have a mixer having balanced low impedance microphone inputs (which is the normal case) and have microphones to suit, the interconnections between the microphones and stagebox are made using balanced microphone cables. These are cables specifically designed to handle microphone-level signals, and usually have a female XLR connector at the end which connects to the microphone and a male XLR at the other end (see the diagram below). These are screened cables, and must not be confused with speaker cables (which are also occasionally equipped with XLRs, but use unscreened cable). These microphone cables may be extended in length simply by plugging two or more of them together.

The connections of a balanced microphone cable

Note that it is important that these cables are wired correctly. The electrical signal from the microphone is carried by the two cable conductors connected to pins 2 and 3 of the XLRs. Although the cable would appear to work correctly if the connections to pins 2 and 3 were reversed (so that pin 2 at one end connects to pin 3 at the other end, and vice versa), the effect would be a signal polarity reversal (often referred to as a phase reversal); this is usually undesirable. The cable conductor that is connected to pin 1 does not carry any signal − this conductor is the 'screen' (or 'shield') of the cable, a metallic mesh or foil whose purpose is to shield the two signal-carrying conductors from interference.

For unbalanced signal sources such as direct feeds from keyboards and guitars (that is, where a microphone is not used), a DI box should always be used. A jack-to-jack cable is usually used to connect the unbalanced signal from the instrument (or from its backline amplifier DI output) to the DI box, which converts the signal into a balanced one suitable for travelling the distance to the mixer. Microphone cables as described above are then used to make the balanced signal connections from the DI boxes to the stagebox.

Regarding which source to connect to which channel of the multicore, see the section below.


Connection of the multicore to the mixer

The mixer end of analogue multicores are usually equipped with 'tails' having XLR connectors which may plug directly into the mixer, or which may connect to the mixer via a patch bay. An alternative arrangement, often used with patch bays, is for the mixer-end of the cable system to be equipped with a multi-way connector. Where a patch bay is used, short cables are used to connect from the patch bay to the mixer inputs.

In systems without patch bays, it is usual for line 1 of the multicore to connect to channel 1 of the mixer, and so on for the required number of channels. In this case, sound sources local to the mixer (tape, CD, etc.) are connected to its higher-numbered channels.

In digital mixer systems employing a digital snake, the snake cable(s) are usually connected directly to the mixer. The mixer provides the facility to map the snake channels to the mixer channels as required.

It is common practice for the drum kit microphones to be allocated to the channels in a 'standard' order, often starting at channel 1 of mixer. These are typically followed by the other instrument channels, then the vocal mics. To enable channels to be rapidly located for adjustment during performances, it is useful to allocate the vocal channels (and sometimes instrument channels) in the same order as the band layout, left to right across the stage. If the multicore channel numbers are to correspond with the mixer channel numbers, then the sources must be connected to the stagebox in the same order that you want them to appear on the mixer. An example channel allocation chart is shown below, for you to adapt to your own requirements. (For example, if your mixer has spare stereo channels then an electronic keyboard instrument could be connected to one of these.)

 1 Kick
 2 Snare
 3 Hi-Hats
 4 Tom (high)   
 5 Tom (low)
 6 Floor tom
 7 Overhead L
 8 Overhead R
 9 Bass
 10 Elec. G
 11 Ac. G
 12 Sax
 13 Keys L
 14 Keys R
 15 Vox 1
 16 Vox 2
 17 Vox 3
 18    Vox 4
 19    Radio 1
 20    Radio 2

Connection of the mixer to the power amplifiers

In the case of powered speakers, their power amplification facilities are provided within the speaker enclosures. So this section is equally applicable to connections between a mixer and powered speakers.

In the case of a powered mixer or a mixer-amplifier, power amplification facilities are provided within the mixer unit. If no additional amplification facilities are required, then you can ignore this section as the connections between the mixing and power amplification parts of that equipment are internal to it. (In such cases, the speakers connect direct to the speaker outputs of the mixer − see 'Connection of the power amplifiers to the speakers' for how to do this).

When the power amplifiers are separate from the mixer, however, line-level interconnections must be made to carry the mixed signals from mixer to the power amplifiers.

When the mixer is located at a good listening point, some distance in front of the speakers, it is usual to locate the power amplifiers close to the speakers (rather than with the mixer), in order to keep the speaker cables short and so avoid significant loss of power and sound quality. In such cases the signal paths from the mixer to the power amplifiers are known as the 'returns'. The returns are often balanced circuits that are carried through the same multicore and stagebox that carries the microphone and DI box signals to the mixer, but in larger systems a dedicated returns multicore and stagebox is used. XLR connectors are generally used for the returns, but they are male rather than female, on the stagebox. Balanced XLR-XLR cables (just the same as microphone cables) are used to connect the returns from the stagebox to the power amplifier inputs.

In cases where the power amplifiers are located adjacent to the mixer (such as when the mixer is on-stage), unbalanced connections (typically using jack connectors) are sometimes used.

Between the mixer and the cables to the power amplifiers is the point at which a graphic equaliser is usually connected, to enable the tonal balance of the final mix to be tailored to the speakers and the acoustics of the room. For a stereo set-up, a graphic equaliser capable of handling both the left and right channels is required. Additional graphic equalisation may be needed for the monitor returns. In larger systems, the graphic equalisers may be connected into the returns via a patch bay.

Large systems usually have separate speakers for the various audio frequency ranges (sub-bass, bass, mid, high), and each of these speakers then has its own dedicated power amplifier(s). This arrangement is called multi-amping, and requires a unit called an active crossover at the amplifier-end of the return cables from the mixer. This unit splits the full-range signal from the mixer into the correct ranges of frequency to feed each amplifier. To get the best overall result, and to avoid damaging the speakers, is very important that the crossover frequencies of the unit are correctly set to match the range of each type of speaker, and that the crossover output-level controls and amplifier input-level controls are also correctly set. Likewise, it is essential to ensure that the various outputs of the crossover are each connected to the correct amplifier.

A more complex system

Connection of the power amplifiers to the speakers

In the case of powered speakers, their power amplification facilities are provided within the speaker enclosures. If all the speakers are of this type then you can ignore this section as the connections between the power amplification and sound-producing parts of the speakers are internal to them. However, if you have slave speakers connected to the powered speakers then what follows is equally applicable to those interconnections.

These connections require the use of cables having a suitably heavy gauge of conductors and fitted with the kind of connectors needed to suit the equipment − usually jack, XLR or Speakon connectors. Do not be tempted to use instrument cables or microphone cables for this purpose − the conductors in these types of cable are often quite thin and may overheat, damaging power amplifiers or even starting a fire, if subjected to the heavy currents drawn by speakers.

It is always recommended to keep the cables between power amplifiers and speakers as short as possible, to avoid unnecessary loss of power and to maintain a high damping factor.

In a multi-amped system (see the previous section), to avoid damage to the speakers it is essential to ensure that each amplifier is connected to the correct type of speaker (sub-bass, bass, mid etc).

Taking into account all the necessary factors when deciding how amplifiers and speakers are to be selected and interconnected can be quite a complex matter, especially in large systems. What's more, if you get it wrong there's a danger of damage to the amplifiers or speakers − or both. See the Amplifiers and Speakers page for further guidance on this subject.


Mains power connections

With the exception of microphones, passive speakers and DI boxes, most PA equipment requires a source of mains power. Due to the high voltage involved, and the consequent risk of electric shock, it is essential that mains supply arrangements are made in a safe manner. Particular safety precautions are required for systems located outdoors or in other hazardous areas (see, for example, RCD).

Additionally, it is essential to ensure that the mains power arrangements are adequate to supply the required amount of current − particularly to the power amplifiers (and to lighting systems, if used). For further information on safety see the Safety page.

Care must be taken in the cabling arrangements to ensure that mains interference does not enter the audio signal chain. This will usually include:

  • Keeping the mains cabling (whether for PA or not) spaced as far as possible from signal cabling, especially on long cable runs.
  • Powering the PA equipment from a separate mains outlet(s) (preferably a separate mains distribution circuit) to those used by interfering equipment (such as lighting).
  • Using the same phase for all PA equipment (including any on-stage equipment), and running interfering equipment from a different phase (if the supply capacity per phase is adequate for this arrangement).
  • Using balanced audio lines wherever possible.
  • Keeping devices that contain audio transformers (e.g. passive DI boxes and microphone splitters) away from mains-powered equipment, especially amplifiers and video monitors.
  • Keeping instruments that employ magnetic pick-ups (e.g. electric guitars and basses) away from mains-powered equipment, such as backline amplifiers.

What do I do now?

Once everything is safely and correctly connected, you are ready to begin the necessary system adjustments and to mix your sound. For guidance on mixing and system adjustments, see the Mixing Engineers page. If you need some explanation of what all the mixer controls are for, see the Mixing Facilities page.


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This page last updated 20-Apr-2017.