Understanding How Main PA, Delay Speakers and Relay Towers Work Together

When attending a large stadium concert, most people assume that all the sound comes directly from the main stage.

In reality, the audio system is distributed across the venue through multiple loudspeaker systems working together as one synchronized network.

If every loudspeaker were installed only on the main stage, audience members seated farther away would hear lower sound levels, reduced clarity and noticeable timing differences. Instead of making the system louder, modern concert engineers divide the venue into multiple coverage zones, allowing every audience member to experience a more consistent performance.

During the construction of the 2026 Guangzhou Pearl Beer Festival Music Festival, we observed how the stadium sound system was distributed from the stage to the rear audience area. This article explains the overall acoustic layout and how each layer contributes to complete sound coverage.

Engineering Observation

During the installation, the following loudspeaker systems were observed:

• Two main line array systems suspended on both sides of the main stage.

• Two additional line array systems installed beside the large LED walls.

• Two delay loudspeaker platforms positioned in front of the Front of House (FOH).

• Relay speaker towers located farther back within the audience area.

Rather than operating independently, these systems formed a coordinated sound reinforcement network covering the entire stadium.

Why Isn't Every Loudspeaker Installed on the Main Stage?

At first glance, it may seem logical to place every loudspeaker on the stage.

However, large stadiums create several acoustic challenges.

As sound travels over long distances, high-frequency energy gradually decreases while travel time increases. Audience members near the stage hear the performance almost instantly, whereas spectators hundreds of metres away hear it noticeably later.

Simply increasing loudspeaker power cannot solve these problems.

Instead, engineers distribute the sound system throughout the venue so that every audience zone is served by the loudspeakers nearest to it.

The goal is not maximum volume.

The goal is consistent coverage.

Layer One: Main PA Covers the Primary Audience Area

The first layer of the system is the Main PA.

In this project, the sound system consisted of more than a single pair of loudspeakers.

Large line array systems were suspended on both sides of the main stage, while additional arrays were positioned beside the large LED walls to improve horizontal coverage across the wider audience area.

Together, these loudspeakers formed the primary sound source for spectators closest to the performance.

Modern Line Array Speakers are designed to control vertical sound dispersion while projecting sound efficiently over long distances. Even so, every system has practical coverage limits, especially inside large stadiums.

Layer Two: Delay Speakers Fill the Middle Coverage Zone

Farther away from the stage, two delay loudspeaker platforms were installed in front of the FOH.

Unlike the main PA, delay speakers do not create a second concert.

They reproduce exactly the same programme material, but with carefully calculated digital delay so that the sound reaches listeners at the correct moment.

Without delay processing, audience members would hear both the stage speakers and the delay speakers at different times, producing echoes and reducing speech intelligibility.

By positioning the delay systems near the middle of the audience area, engineers improve sound consistency while maintaining smooth transitions between coverage zones.

Their location also complements the engineering role of the Front of House (FOH), where the entire audio system is monitored and adjusted during the performance.

Layer Three: Relay Towers Extend Coverage to the Rear Audience

For spectators located even farther from the stage, relay speaker towers provide the final layer of reinforcement.

These tall temporary structures support additional line array loudspeakers positioned much closer to the rear audience than the main stage itself.

Because the loudspeakers are physically closer to these listeners, engineers can achieve better clarity and more uniform sound pressure levels without relying solely on extremely high output from the stage.

During this project, the relay towers stood approximately 20 metres high and incorporated steel bases, aluminium truss masts, water ballast, guy wires and extended outriggers to provide the required structural stability.

The engineering design of these temporary structures is discussed in detail in our article Why Are Relay Speaker Towers Needed?.

One Stadium, Multiple Coverage Zones

Rather than treating the stadium as one enormous listening area, sound engineers divide it into several overlapping coverage zones.

Each layer supports the next, allowing the entire venue to function as one integrated sound system.

Coverage Is More Important Than Volume

One of the biggest misconceptions about large concert sound systems is that adding more loudspeakers simply makes the concert louder.

In professional live production, the opposite is often true.

Additional loudspeakers are primarily installed to improve coverage consistency.

A well-designed system allows spectators seated near the stage and those hundreds of metres away to hear similar tonal balance, speech intelligibility and musical detail.

The objective is to deliver a consistent listening experience—not simply higher sound pressure.

This philosophy guides the design of complete Stage Sound systems for concerts, festivals and large outdoor events.

Engineering Observation and Interpretation

The layout observed during this project illustrates a typical layered reinforcement strategy:

Main Stage

↓

Main PA

↓

Delay Speakers

↓

Relay Speaker Towers

↓

Complete Audience Coverage

Rather than depending on one extremely powerful sound source, engineers gradually distribute reinforcement systems throughout the venue.

Each layer extends the effective listening area while maintaining continuity with the previous one.

This approach reduces acoustic inconsistencies and allows the entire stadium to function as one coordinated sound environment.

Understanding the System as a Whole

Viewed individually, the Main PA, delay speakers and relay towers appear to be separate pieces of equipment.

In reality, they operate as parts of one synchronized system controlled from the FOH.

The main arrays establish the primary sound field.

Delay speakers reinforce the middle audience area.

Relay towers extend coverage to the farthest spectators.

Together, these systems transform an enormous stadium into a venue where thousands of people can share nearly the same listening experience.

Understanding this layered approach also makes it easier to appreciate the engineering decisions behind other temporary concert structures, including the overall stadium layout and the reasons large concerts are built inside stadiums.

Conclusion

A modern stadium concert does not rely on one enormous loudspeaker system.

Instead, it uses multiple synchronized reinforcement layers strategically distributed across the venue.

Main PA systems provide the primary coverage.

Delay speakers maintain consistency through the middle audience areas.

Relay speaker towers extend reinforcement to the rear of the stadium.

Working together under the control of the FOH, these systems ensure that sound remains clear, balanced and synchronized from the front row to the farthest seat.

Rather than making the concert louder, this distributed approach makes the listening experience more consistent—one of the defining principles of professional stadium sound engineering.