A sound system for a large outdoor event is not chosen exclusively based on the number of participants or the power of the amplifiers. The most important factors are geometry and audience depth, required SPL and system headroom, the character of the program, directivity of the sets, subwoofer configuration, need for frontfills or delay line, weather conditions, and limiting sound emission outside the event area. For large systems, the design should be verified in advance using electroacoustic prediction.

What does the choice of sound system for a large outdoor event really depend on?

The choice of the PA system should primarily result from the fact that, what space needs to be covered with sound and what level and character of sound should be achieved in that space.. The number of participants is useful organizational information, but it does not describe the electroacoustic task by itself.

Size and geometry of the audience area

The first necessary piece of information is the site plan. The width and depth of the audience, the location of the stage, barriers, VIP sections, food stands, tents, grandstands, FOH, and all elements that can influence the placement of the system are important.

A rectangular audience area measuring 40 × 100 m presents different requirements than a wide space of 100 × 40 m, even though the area may be identical. In the first case, the greater challenge is usually effective and even coverage of distant sectors. In the second, wide horizontal dispersion or the use of additional outfills may be significant.

The number of participants and the actual system requirements

The number of people helps determine the scale of the event, but it does not allow for a clear selection of the PA. Ten thousand people concentrated in a relatively compact space may be an easier task than a smaller audience stretched over a very deep area.

Therefore, the question "what system for 5000 people?" has too little data. The company preparing the sound system for concerts and outdoor events should also ask about the site plan, program, expected location of the audience, and sound level requirements.

Concert, DJ, speeches – different requirements for SPL and bandwidth

The system for a rock concert, electronic festival, and an event with speeches does not have to look the same.

At an event primarily based on speech, the priority is very good intelligibility and even coverage. A concert requires greater dynamics, a wide range, and appropriate headroom. Electronic music can however impose particularly high demands on the low-frequency section.

This does not mean that there is one correct set for every genre. The event program defines the system requirements, not the name of the speaker model.

The distance from the nearest to the farthest listener

A large difference between the distance of the first and last row from the system is one of the most important design issues.

The goal is not simply to achieve a high level at the back of the audience. It must be done without creating unnecessarily high SPL in the front rows. That is why in large systems, directionality, array geometry, suspension height, and the division of space between the main PA, front fills, and delay systems are so crucial. 

How to determine the required SPL level and system headroom?

 The required SPL should result from the nature of the program, the expected dynamics, and the size of the audience area. A well-designed system should not operate at the limit of its capabilities throughout the concert.

Continuous, peak SPL, and headroom

SPL, or sound pressure level, is not a single number that describes everything. In practice, the level that the system can maintain during the program, and the ability to reproduce short-term peaks without compression, limiting, or excessive distortion is what matters.

Headroom is the margin between the typical operating level and the system's limits. It is needed, among other things, for the proper reproduction of snare, kick, vocal transients, or dynamic changes in music.

A system that theoretically reaches the expected level, but must constantly operate on limiters, is poorly suited for the task.

Why do watts alone say little about the system's capability?

The amplifier's power does not directly indicate what SPL the audience will receive. The result also depends on the efficiency of the sets, their maximum output level, directivity, configuration, number of elements, mutual coupling, and distance.

Comparing two systems solely based on the sum of watts is therefore a very weak method. In a professional project, what matters is the achieved level and coverage in a specific area, not the sum of values printed on the amplifiers.

Level drop with distance

Sound loses level with increasing distance, but the actual behavior of the system depends on the nature of the source, frequency, and configuration of the sets. For an ideal point source in free field, a drop of about 6 dB is assumed when the distance is doubled. In the case of a properly functioning line source in its near field, the drop may approach 3 dB per doubling of distance, but a finite line array transitions with frequency and distance to behave characteristic of the far field.

Therefore, the principles of "line array plays twice as far" or "just add more modules" are too much of an oversimplification. An analysis of the specific system and its geometry is needed.

Line array or point source for a large outdoor event?

 Line array is not automatically better than point source. The decision should be based on the geometry of the audience, required directivity, distance, and the possibility of system placement.

When does the length of the audience favor a line system?

The line array system is particularly useful when it is necessary to control energy vertically and handle a significant distance difference between the nearest and farthest sections of the audience.

The length of the array, the angles between the elements, and its height affect the behavior of the source depending on frequency and distance. Therefore, a line array should be designed as a whole, not as a random collection of "a large number of boxes." L-Acoustics indicates that when designing a line source, one must balance coverage, SPL, and frequency response, and the physical geometry of the array has a direct impact on the result.

The article discusses the differences in more detail Line array or point source – when to choose which sound system?

When can a point source be a better solution?

A point source can be a very good solution for areas with less depth, wide audiences, smaller stages, or applications where a single set provides adequate dispersion and level.

It can also serve as a fill or auxiliary system in a large configuration. The mere fact that an event is "large" does not mean that every PA element must be a line array system.

Directionality is more important than the number of sets themselves

Adding additional speakers without controlling their mutual interaction can worsen the system. Overlapping sources create interference, causing the response to change depending on the location in the audience.

Therefore, the design starts with the question: where should the energy go, and where should it not go? Only then is the number and type of sets chosen.

How to ensure even coverage for the entire audience?

 A large outdoor event often requires dividing the task among several cooperating systems. Attempting to cover the entire area solely with the main PA may result in too high a level at the front and still insufficient levels in problematic areas.

Main PA

Main PA is the primary system covering the main part of the audience. Its position, height, dispersion, and geometry are the foundation of the entire project.

Main should provide as much of the needed coverage as possible without excessively sending energy beyond the audience.

Frontfill

Frontfills serve areas very close to the stage that may be below or outside the proper coverage of the main system.

Their task is not simply to "add volume". They should fill in the missing area while maintaining the appropriate time and tonal relationship with the main PA.

Outfill

Outfills are used to extend coverage to the side sectors of the audience that are not covered by the main system.

They are particularly useful for wide audiences. However, if misconfigured, they can create large overlapping areas with the main PA, so their range should be determined by the design.

Delay line

A delay line is an additional system set further from the stage and delayed relative to the main PA so that the sound reaches the listener in the proper time relationship.

Instead of trying to send all the needed SPL over a huge distance from the stage, energy can be delivered closer to the further audience. This helps improve level uniformity and often reduces the need for very loud playing from the main system.

This topic is further developed in the article How to sound a long hall or large space using a delay line?

Special zones and problematic areas

In the real area, there are also stands, side sectors, VIP spaces, or areas obscured by infrastructure elements.

The project should take them into account before installation. Adding another speaker only when it turns out after the event starts that "nothing can be heard here" is a much worse method than prior analysis of the space.

How to plan the low-frequency section?

 The subwoofer section is a separate element of the project, because low frequencies behave differently than the range reproduced by the main system. It is not enough to count the number of subwoofers – you also need to plan their placement and directionality.

How many and what subwoofers are needed?

The number of subwoofers depends, among other things, on the program, the required level, the size of the area, the capabilities of specific sets, and the chosen configuration.

An acoustic concert and an electronic music festival may require a completely different reserve in the low-frequency range. Therefore, there is no universal conversion of "one subwoofer per X people".

More details can be found in the material How to select subwoofers for a concert and outdoor event?

Classic layout, cardioid, and end-fire

Several subwoofers can be configured in different directional layouts. Cardioid systems use the positioning of elements and appropriate signal processing to reduce the level emitted in one direction, e.g. behind the system. Meyer Sound documentation shows, for example, gradient configurations using elements directed forward and backward along with polarization differences and delays.

End-fire, on the other hand, uses spatial separation elements and delays to achieve directional interference. There is no one setting that is right for all subwoofers and every frequency – the configuration needs to be designed for a specific system.

Limiting bass behind the stage and outside the event area

Low-frequency control can improve not only the audience's comfort but also the conditions on stage and the situation outside the event area.

If significant low-frequency energy is also sent to the back, it can reach the stage, the technical backstage, and towards the structure located on the opposite side of the audience. A directional configuration of subwoofers allows reducing some of this energy, although it does not mean a total "turning off the bass" outside the system's axis.

How does the weather affect outdoor sound reinforcement?

 Weather conditions affect sound propagation, especially over long distances. A system that performs very well during a soundcheck in the afternoon may operate under different conditions in the evening.

Temperature and humidity

Atmospheric absorption depends, among other things, on frequency, temperature, relative humidity, and pressure. The ISO 9613-1 standard describes the method for calculating sound attenuation resulting from atmospheric absorption as a function of these parameters.

The effect is particularly significant for higher frequencies at long distances. This does not mean that the engineer should "turn up the highs" every time the temperature changes. Modern workflows can take into account atmospheric data already at the prediction and configuration stage.

Wind and sound propagation over long distances

The wind does not act on the entire system like a simple volume controller. The gradient of wind speed and temperature changes with height can bend the path of sound propagation, causing conditions to vary depending on the direction.

In a small event, the difference may be less noticeable, but in a large audience, problems that arise over the next several dozen meters can be significant.

That is why one should not design a large outdoor event based on the assumption of ideal, still air and assume that conditions will remain the same throughout the day.

Protecting equipment from rain

The resistance of individual components depends on the design and the manufacturer's specifications. One should not automatically assume that every concert speaker can safely operate during rainfall.

The technical design should consider not only the PA, but also amplifiers, racks, connection points, distribution, FOH, consoles, stage boxes and other electronics. The procedure for sudden weather changes should be established before the event, not at the moment the rain starts.

Noise outside the event area – how to plan the system responsibly?

A good outdoor system should deliver the necessary energy primarily where the audience is located. The more sound that goes in other directions, the harder it is to control the event's impact on the surroundings.

Directional control

The directionality of the system allows for limiting the energy sent to unnecessary areas. This applies to both the proper positioning of the main PA, as well as the fills and delayed systems.

A "bigger system" is not always the best solution. Often, better placement of sources and more precise coverage proves to be more effective.

The importance of subwoofer placement

Low frequencies are particularly problematic from the perspective of emissions outside the audience. Due to the long wavelength, individual subwoofers usually have a wide directional characteristic.

Therefore, directional configurations can be one of the tools used to manage emissions. However, their performance must be evaluated across the entire relevant frequency range, not just at a single frequency.

Prediction of sound emissions outside the audience

Software can be used not only to check SPL at the audience but also to predict sound propagation in the environment. For example, d&b NoizCalc uses system data, terrain modeling, and computational methods such as ISO 9613-2 to create maps of the predicted noise level around the event.

This allows for evaluating system setup options even before installation and searching for configurations that provide the necessary level at the audience with minimized emissions in unwanted directions.

Why should the system be designed before arriving on site?

Large outdoor sound systems should have a design prepared before the installation begins. On-site, verification and tuning are performed, but fundamental decisions regarding geometry, the number of elements, or suspension points should not be made through trial and error.

Terrain and audience model

The first step is to map the audience area. In professional software, listening surfaces can be defined and a spatial model can be built.

ArrayCalc allows for modeling audience areas and predicting line array, point source, and subwoofer systems, while Soundvision enables the placement of arrays and subwoofers in a 3D model and checking the expected SPL distribution.

SPL Prediction

The prediction map shows how the designed system should cover individual parts of the audience.

This is not a "pretty colorful picture for the offer." It allows comparing configuration variants and checking, among other things, whether there is a large drop in level at the end of the area, whether an unnecessarily high SPL is created in front of the stage, and where additional sources are needed.

Mechanical design and suspension points

In a suspended system, the acoustic design must comply with the permissible mechanical configuration of the system and the structure on which the array is to be suspended.

Weight, number of elements, angles, height, and loads are not matters for improvisation. The system software can also provide information related to rigging and positioning of the arrays; d&b lists rigging and safety parameters directly as part of the tasks performed in ArrayCalc.

Verification during system tuning

Prediction does not replace measurements. After setting up the system, it is necessary to check whether the physical implementation corresponds to the design, and then verify the time relationships, levels, and system response.

This particularly concerns the connection of the main PA with frontfills, outfills, delay lines, and subwoofers. Only after this verification can one speak of a complete system startup.

What data should be provided to the sound company before the quote?

The more accurate information the contractor receives, the less risk there is that the offer will be based on guessing. To prepare the project and estimate for a large outdoor event, it is worth providing primarily:

• the date and location of the event,
• the type of event and program,
• the expected number of participants,
• a plan of the area with dimensions of the audience zone,
• the dimensions and position of the stage,
• information about the stands, side sectors, and other zones,
• the technical rider of the artists, if available,
• the schedule of concerts, rehearsals, and band changes,
• information about noise emission restrictions,
• available hanging points or stage structure,
• requirements for FOH, monitors, and communication,
• information about power supply and technical infrastructure.

If some data is not yet known, it is worth at least providing the current version of the plan. The entire process is detailed in the material What information is needed by the sound company to prepare an estimate?

A well-prepared offer for the sound system for the outdoor event should be based on this data and show a thoughtful configuration, not just a list of speakers. powinna wynikać z tych danych i pokazywać przemyślaną konfigurację, a nie tylko listę głośników.

The most common mistakes in sound reinforcement for large outdoor events

The biggest problems usually do not arise from one "too small speaker," but from incorrect design assumptions. The most common mistakes include:

• selecting a system only based on the number of participants,
• comparing PA solely based on watts,
• lack of a model and predictions for a large audience,
• attempt to cover very deep terrain solely with main PA,
• lack of frontfills or outfills where geometry requires them,
• incorrectly designed delay line,
• random placement of subwoofers,
• lack of emission control behind the stage and outside the event area,
• failure to consider weather conditions,
• too little system headroom,
• lack of appropriate data before preparing the estimate,
• treating tuning as an attempt to fix errors resulting from the physical setup of the system.

Good processing can improve a lot, but DSP cannot replace proper system geometry. If the speakers initially direct energy to the wrong places or create unfavorable interferences with each other, electronic correction has limited capabilities.

Summary

A PA system for a large outdoor event should be designed based on the terrain and event requirements, not on the number of participants or total amplifier power. The most important factors are audience geometry, distances, required SPL and headroom, directivity, event program, and the proper division of tasks between main PA, frontfills, outfills, delay line, and subwoofer section.

For large productions, weather conditions and control of sound emission outside the audience area also become significant. Electroacoustic prediction allows for project assessment even before installation, while measurements and tuning serve to verify it after the system is built.

Therefore, when choosing a company that implements sound for concerts and outdoor events it is worth asking not only about the speakers they have, but also about the design method, prediction, configuration of auxiliary systems, and the process of setting up the PA.