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What to Consider Before Hiring PA System
It may be a loose analogy, but looking for ‘a pa system’ can be compared with looking for ‘a vehicle’: do you need it to move furniture, or to deliver the bride to the church? The PA system you use needs to be appropriate for its purpose, and what will suit an after-dinner speaker in a conference-room may not be the best thing for Thrash Metal in a warehouse.
If you have been tasked with sourcing a PA system for an event, you may be faced with choices involving unfamiliar equipment, specified in unfamiliar terms. While most reputable PA Hire companies will be able to offer some help with these, you may also wish to understand competing quotations, or to satisfy yourself - if deciding on the basis of cost, for example - that the least expensive system will still meet the requirements of the event, the venue, the performers, and the audience.
As far as cost is concerned, you should also keep in mind that - all else being equal - ‘more’ (as in more microphones, monitors, output level, or anything else that can be quantified) means ‘more expensive’, and ‘better’ (as in better microphones, monitors, loudspeakers, or anything else that varies in quality) almost always also means ‘more expensive’. Most of us cannot afford to make choices on the basis of quantity and quality alone, so that in practice the best possible product usually means the best affordable product (which is not the same thing as the most affordable - i.e. cheapest - product).
Faced with the range of possible variation, it isn't possible to provide a ‘one size fits all’ solution to the problem of deciding what to get and where to get it. This section is therefore focused instead on the type of questions you may need to ask.
What you may need to find out is dealt with under Event Information, below, but what you know is often less useful than knowing where to look.
For information about equipment, see our Equipment Guide section, or consult manufacturer websites for details about specific makes and models. Event-specific information can usually be obtained from the following sources (any of which may fulfil more than one role, or have access to information from one or more of the others):
The promoter is whoever is putting on the event, and should be able to tell you
This is where the event will be happening, and the relevant contact there (usually the technical manager or technician, rather than the box-office staff) should be able to tell you
For professional performers or public speakers at large-scale events you will usually need to speak to their technical agent or sound-engineer (or other production personnel). Amateur, semi-professional or smaller-scale professional acts will more commonly delegate the role of technical contact to a band-member or follower. They should be able to provide you with
This is often a key document for any touring act, but is often unreliable. Common problems are that it is:
However, while the good news is that ‘worst-case’ might not be as bad as it looks, the bad news is that the technical rider may form part of a legally-binding contract, so you might have to meet it to the letter. Generally - even if you can meet it to the letter - it is a good plan to check with the band before you base any assumptions or irreversible decisions on it.
The PA company will be able (and should be prepared) to tell you
Your starting-point in deciding what you will need is with the event itself. Key information, which you should be able to obtain from the sources described above, lies in three main areas: programme content, the venue, and the timetable.
You need to know what the event involves: how many acts, what each act comprises, and what their technical requirements are.
How this affects the PA system can be covered under four main headings: input requirements, processing and effects, output mixes, and output capacity.
It is as well to allow enough input equipment to cover every source even where they may not be needed (for example, a band in a small venue might not need a microphone on every drum, or on electric guitar amplifiers or bass guitar), as you don't have to use what is available, but you can't use what is not.
As well the input equipment itself, you will need a mixer with enough input channels to accommodate all of it. After totting-up the channels you will need for sound sources, you should add at least another couple of channels for effects before arriving at the total number of mixer inputs you will need.
Depending on the event schedule (see Timetable, below), events using an analogue mixer with multiple acts may call for a mixer with enough channels to cover at least two consecutive acts (and for that reason it may be better not to schedule the two largest acts consecutively if there is any way round it). Most digital mixers allow channels - as well as other settings - to be instantly reconfigured, so needing more channels for multiple acts is less likely to be an issue with a digital mixer.
It is usually possible to share some equipment and channels in multiple-performance events, whether this is for speech-only (e.g. stand-up comedy) or large musical ensembles, but especially with multiple speaking events you need to ensure that there are at least enough microphones for the maximum concurrent number of speakers, and it is a good idea to add one to that number to allow for a presenter or MC. Radio microphones are often best for speech-only applications, as they allow mobility, and keep the stage and access routes free of cables.
Graphic EQ is required to correct frequency irregularities in the PA system as a whole, and to minimise its interaction with room reflections and resonances. All PA systems should ideally include a 31-band graphic EQ channel for every output channel, with the possible exception of a system with a very flat frequency-response and no monitor subsystems being used outdoors.
Generally, at least enough compressor channels for vocals will be required for musical styles with high output levels, and compression is often desirable for other sources. Compression is available for all input channels on most modern digital mixers, but offboard compressors will usually be required for analogue-based systems.
You will almost certainly cover requirements if you allow one mix per performer in the largest ensemble, but other than for the most demanding performers or situations you will probably be able to manage with less than this: for spoken (e.g. stand-up or theatrical) productions, a single stage mix will probably suffice, while for large bands a single mix for some sections will often be enough (e.g. one mix for a three-piece brass section), although lead parts will usually still need an individual mix.
What this means in practice is that you need to ensure that the main mixer (if it is also being used for monitors) or monitor mixer (if a separate mixer is needed for monitors) can provide enough pre-fade mixes for the largest number required by any individual act, and that enough separate amplifier channels and monitor loudspeakers (or in-ear systems, as appropriate) are available for that number of mixes. Here, it is always better to refer to technical riders or speak to the band's technical representative or sound-engineer than to guess or assume. In the absence of any clear information to the contrary a four-way monitor system is a fairly common basic default (and fairly safe if the largest band is a four-piece), and many larger bands that would prefer more can cope with four on-stage mixes. On smaller stages (from pubs and village halls to provincial arts centres) it may be difficult to achieve sufficient separation with a much larger number. However, more than a minimal number of mixes will often be advantageous, while less may compromise the performance and - if it is your call - your relationship with the band.
Speech-only and acoustic music systems do not generally need extended bass reproduction (the lowest fundamental on an acoustic guitar in dropped-D tuning is 73 Hz, for which most ‘full-range’ 10″ or larger cabinets will be adequate).
You will also need to take account of the distance from auditorium loudspeakers to far audience positions before you can calculate what the PA system's sound level there will be. This is covered in the section on the venue, below.
Venues range in size from bijou bars to stadiums, and may have hosted events for years, or - like a marquee in a private garden for a wedding, or parish hall for a local fund-raising event - may be used (or even constructed) for a single occasion.
Venues with a long event history will probably be able to make recommendations based on their experience, while the bride's father - who has never previously put on a band in a marquee in his garden - may not. However, the venue impacts on sound system requirements in two main ways: size, and layout.
Venue size determines the distance from loudspeaker cabinets to a typical audience position, and enables you to calculate the reduction over distance in the system's direct output level. For small to medium-sized venues you can calculate the capability you require either by multiplying speaker cabinets of known peak output level, or hiring speaker cabinets with greater output capability.
To calculate the audience position level for a known cabinet output (dB SPL @ 1 metre), reduce the level by 6dB for every doubling of distance, or by 20dB for every tenfold increase of distance. For example:
*20 metres represents 2 × 10 × 1 metre, so one doubling of distance loses 6dB, and a further tenfold increase loses a further 20dB. Note that any increase in cabinet output adds directly to the distant level, so that a loudspeaker with a peak output level of 131dB (SPL) would achieve a peak SPL of 105dB in the same position.
To calculate the number of speaker cabinets required to reach a higher audience level, add 3dB for every doubling of speaker cabinets. For example:
†2 × 1 cabinets = 100 + 3dB = 103dB; 2 × 2 cabinets = 103 + 3dB = 106dB.
This method has some drawbacks, the most significant of which is poor phase alignment between separate speaker cabinets, which can produce directly audible effects to audience members if they move around, and produce other artefacts - tonal colouration and reduction in intelligibility - even where the audience is stationary.
Generally, therefore, it is better to use higher-output loudspeaker cabinets (or cabinets which are specifically designed to be arrayed in multiples) where the overall level requires more than two cabinets - or two stacks if a multi-enclosure system is used - per side.
With larger audience areas the practical choices are limited: using only clustered speakers in front of the stage results in very uneven levels between front and back positions in the audience (it is much too loud near the stage, and not loud enough at the back).
Before the advent of line-array systems the solution was to have secondary (delayed) speakers or clusters part of the way into the audience area. This method brings several headaches, principally finding safe positions for secondary systems in the audience area that do not block audience sight-lines to the stage, and running cable to them. Currently, for audience sizes of more than a couple of thousand, line-array speaker systems are the most straightforward option, and the best solution in acoustic terms, but delay clusters may still be required for greater distances.
Generally, you should hire a system that will comfortably manage the required output level (i.e. with several dB of headroom), but you can see from the calculations above that if you want 3dB of headroom you need twice as many cabinets. This won't double the budget, but will certainly increase it substantially.
For other types of space, additional subsystems (possibly also requiring delays for time-alignment) may be required, especially where there are areas that obviously fall outside the area covered by the main loudspeakers or arrays. Examples are:
A majority of concert venues with balconies or outlying audience areas have in-house loudspeaker fills for those areas, and it is often possible to link to these from a touring system, which will save considerable set-up time and additional cost. However, this requires careful checking with both the PA company and the venue: do not assume that either will accept using the other's equipment as an acceptable solution for your specific event, or will be able to align one system with the other without additional time or equipment.
Time can be limited before and/or during and/or after an event. Working within time constraints may mean that you need different equipment, more personnel, or both.
In general, if there isn't enough time between venue access and audience admission, or between the end of the event and venue curfew, you will need extra crew. Larger capacity venues usually also require more set-up (and take-down) time, and while some sound systems are easier to install than others, you will need to factor-in enough crew to get this done in the time available. Just adding bodies may not be enough: local helpers are often much less effective than trained and experienced sound company crew, and doubling their number may not speed things up at all.
If there isn't enough time for programme-dependent changes during the event, solutions are more likely to involve a combination of equipment and crew: digital mixers allow faster scene-changing than their analogue predecessors, and may be essntial where time between acts is very short; additional microphones and other input equipment may also be called for, to save time that would otherwise be required to move microphones (from one drum kit to another, for example) or repatch stage-boxes.
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