PA Hire Guide

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.

Information Sources

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

The promoter is whoever is putting on the event, and should be able to tell you

  • Where the event will be
  • Who to contact at the venue
  • Who will be performing or appearing
  • Who their contact is
  • The event schedule.

The Venue

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

  • The size and layout of the auditorium
  • Audience capacity
  • Access times for setting up and dismantling equipment
  • Load-in routes and parking areas
  • Any technical issues or restrictions (like 230V/415V supply points and whether haze machines are permitted).

The Performers

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

  • A technical rider, or at least
  • A channel list and stage plan, or at the very least
  • Their line-up, instruments and vocalists.

The Technical Rider

This is often a key document for any touring act, but is also often unreliable. Common problems are that it is:

  • The wrong document. A band may have a ‘stadium’ rider and an ‘arts-centre’ rider, and send the former out for your event in a 200-capacity venue.
  • Out of date. The one for their tour of Europe two years ago is not only for bigger venues, but includes a guest keyboard-player and second guitarist that were only there for that tour.
  • A wish-list. On their brief support-tour last year with The World's Largest Megaband they asked someone what the £2,000 microphones, £50,000 mixer and £2,000,000 loudspeaker system were, and put those on their rider.

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

The PA company will be able (and should be prepared) to tell you

  • What actual equipment will be provided. Do not assume, if a loudspeaker make and model is specified on the rider, that some unspecified make or model is a suitable replacement, especially if the rider does not include the words ‘or equivalent’.
  • What it will cost with/without matching the rider exactly, and if something different is suggested, what difference it makes.
  • Whether they are familiar with the promoter, the venue, or the performers.

Event Information

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.

Programme Content

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.

  1. Input Requirements. The PA system needs to have at least enough input equipment (microphones, microphone stands, DI boxes and cables) to cope with whatever part of the programme has the greatest number of sources, and the equipment must be suitable for the sources. In a programme with multiple performers, you will also need at least enough vocal microphones for the act with the most vocalists, and at least enough of everything else (instrument microphones, stands and DI boxes) to cover the most demanding requirement for each. In the absence of any specific information from technical riders or elsewhere, you need to tot up:
    • Vocals. If faced with a choice of microphones, you will generally be OK with Shure SM58s, which have survived the best part of 50 years as the most popular vocal microphone in the industry. Most vocalists will accept these (or Shure's Β58A as an improved but not always preferred alternative), but many will be less happy to use other makes and models, even if these are arguably ‘better’.
    • General purpose dynamic microphones. Here, the Shure SM57 or Β57A is a good choice for anything with a relatively high acoustic output (e.g. drums, brass, accordions, or guitar or keyboard combos). Although an SM57 will cope in an emergency, the kick-drum will benefit from having its own dedicated microphone, and popular choices include the AKG D112, Shure Β52A or Β91A, and EV RE20.
    • General purpose condenser microphones. Greater microphone sensitivity is needed for low-output acoustic instruments (e.g. acoustic guitars), and sources with high-frequency detail (e.g. flutes and cymbals). A good well-established all-rounder is the AKG C1000S, but there are very many suitable (and in some cases better) alternatives.
    • DI Boxes. You need one for each mono electronic source (or two for any stereo sources). Here, makes and models abound, but you'll be safe with e.g. the BSS AR-133.

    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.

  2. Processing and Effects. As well as amplification, some additional audio processing is usually required between the PA system's inputs and outputs, and effects - principally reverb and/or delay - are almost always needed for live music (but generally not for speech or recorded music). The programme content will determine the type and extent of processing and effects that are necessary or desirable, and with live music you will usually find this specified on technical riders. In general, however, in descending order of importance, the PA system will need:
    • Equalisation. Equalisation (EQ) is required for all types of programme content. This is generally found in two places: mixer channels and graphic equalisers. Channel EQ is required to correct frequency irregularities in input equipment, and even for relatively undemanding speech-only events you should ensure the mixer has at least high, low and sweepable mid-frequency controls. A single sweepable mid can deal with the most prominent problem frequency, but ideally the mixer should have two sweepable midrange controls.

      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.

    • Effects. At least a single reverb (usually in the form of an external effects unit, but some mixers include an effects section) will be required for all but speech-only events. Two banks of effects, allowing at least one reverb and one other effect (e.g. echo) to be used simultaneously, is a fairly safe basic default option.
    • Compression. Compressors are needed for any source sound whose dynamic range is greater than the dynamic range of the system as a whole, or of its place in the context of musical arrangement. This applies, for example, to vocals with relatively high-volume backing instruments, where the minimum vocal level for intelligibility needs to be be at least equal to instrument levels, while the maximum vocal level may be limited by system output capability or by what the audience will find comfortable.

      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.

    • Gating. Noise-gates are frequently required for drums (but rarely for anything else in live music). Most compressors include a basic gating function (which may be a satisfactory alternative), and most digital mixers include gating on every input channel, but if neither are available you should allow for at least enough noise-gate channels to cover the kick-drum and all tom-toms.
  3. Output Mixes. As well as outputs for the auditorium, most performance styles - even some spoken varieties - require monitor mixes: some or all of the performers will need to hear specific mixes of their own and/or other performers’ voices and instruments on stage.

    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.

  4. Output Capacity. The programme content will indicate, if it does not actually determine, how loud the PA system needs to be in a typical audience position. It should be fairly self-evident that a loud rock band will require a PA system with high output and an extended low-frequency range, where a public meeting will not. Some technical riders - especially those for bands with louder styles - will state the required level at the mixer position (which should be located so that the sound-engineer can hear what a typical audience member hears), which will enable you to work to a known number. Otherwise, for the following applications, systems capable of the accompanying peak levels in far audience positions will generally be adequate:
    • Speech only - 80-90 dB (SPL)
    • Acoustic Music - 85-95 dB (SPL)
    • Folk Rock/Dinner Dance - 90-105 dB (SPL)
    • Blues/Rock - 100-110 dB (SPL)
    • Metal/Louder Styles - >110 dB (SPL)

    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. While descriptions of the calculations involved are covered in the section on the venue (below), you may find it easier to use the functions on our PA System Calculations page.

The Venue

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.

  1. Venue Size. Sound emanating from any source diminishes over distance. The sound system needs to be capable of projecting levels for the respective styles discussed in the previous section to the furthest listening positions. What is adequate for a 10m × 20m village hall may not be enough for a 50m-deep outdoor area (and what is adequate for the latter will be overkill for the former). If you need a PA system for a variety of venues (for a tour, for example), it must be adequate for the largest of them, although in that case a scalable loudspeaker system that can be adapted to different venue layouts and sizes may be required.

    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:

    1. Speaker cabinet output (Peak SPL @ 1m): 126dB
    2. Distance from speaker to audience position: 20m
    3. Level (Peak SPL) @ 20m: 100dB*

    *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:

    1. Single speaker cabinet at 20m: 100dB
    2. Required level: 106dB
    3. Number of speaker cabinets required: 4†

    †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 who 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) than simply adding more loudspeakers.

    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.

  2. Venue Layout. Many events are put on in rooms that are essentially a rectangular box, and for these a single pair of cabinets or clusters at either side of the stage or performance area (with whatever bass cabinets or array are required) will generally suffice, unless:
    • The room is longer than about 30 metres (from audience front row to back row), in which case a conventional loudspeaker system may need to be supplemented with delay speakers to minimise level variation over the length of the room;
    • Reflected sound takes longer than a couple of seconds to decay (−60dB), in which case delay speakers may be advisable to reduce excitation;
    • The width of the stage or performance area means that there is a gap in loudspeaker cover for the front central section of the audience, in which case additional ‘centre-fill’ loudspeakers may be needed;
    • The width of the audience area means that the outer front sections of the audience fall outside the main system's area of cover, in which case additional ‘side-fill’ loudspeakers may be needed;

    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:

    • Theatre-style spaces with side or tiered sections;
    • Audience areas that are substantially wider than the stage, or extend into areas alongside the stage;
    • Events where the sound needs to be relayed to other rooms.

    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.

Event Timetable

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.

See Also...

Our PA Hire Checklist for what any reputable PA hire company should willingly provide.

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