Understanding How Relay Towers Deliver Consistent Sound Across Large Stadium Concerts

When attending a large stadium concert, most people focus on the main stage. However, if you look farther into the audience area, you will often notice several tall towers supporting additional line array speakers.

Many people assume these towers simply make the concert louder.

In reality, that is not their primary purpose.

Relay speaker towers exist because even the most powerful main stage sound system cannot provide consistent, high-quality audio across an entire stadium. Without them, spectators seated far from the stage would experience lower sound levels, reduced speech intelligibility and a noticeable delay between what they see and what they hear.

During the construction of the 2026 Guangzhou Pearl Beer Festival Music Festival, we observed one of these relay speaker towers in detail. Its structural configuration reveals how temporary event engineering balances acoustics, structural stability, transportation efficiency and installation safety.

Engineering Observation

The relay speaker tower observed during this project featured several distinctive characteristics:

• Approximately 20 metres in overall height

• Black steel base and black steel top section

• Heavy-duty aluminium pin-connected truss mast

• Eight diagonal braces extending from the base to the main mast

• Four large water tanks positioned symmetrically around the base

• Guy wires extending from the top section to each water tank

• Extended steel outriggers bolted to the primary base frame

• Multiple adjustable leveling feet beneath the steel base

Although these features may appear unrelated, each contributes to the tower's structural performance.

Why Can't the Main Stage Speakers Cover the Entire Stadium?

Many people assume that simply installing larger loudspeakers on the main stage would solve the problem.

Unfortunately, sound does not behave that way.

As sound travels through the air, high frequencies lose energy much faster than low frequencies. Over long distances, music gradually becomes less detailed and speech becomes harder to understand.

In addition, sound takes time to travel.

Audience members standing close to the stage hear the main speaker system almost immediately.

Spectators hundreds of metres away hear the same sound noticeably later.

A modern Line Array Speaker system is designed to project sound efficiently over long distances, but no single loudspeaker array can maintain identical sound quality throughout an entire stadium.

This is why large concert productions introduce relay speaker towers to reinforce distant audience areas.

Relay Towers Are Not Louder Speakers

The word "relay" is important.

These towers are not installed to increase volume.

Instead, they reproduce the same programme material at carefully calculated locations, allowing the audience farther from the stage to hear sound that arrives at nearly the same moment as the sound from the main system.

This approach creates a much more uniform listening experience across the venue.

Modern delay processing ensures that every relay loudspeaker works together with the main system rather than competing against it.

Relay towers therefore become an essential part of the overall Stage Sound design rather than independent sound systems.

Why Was the Tower Approximately 20 Metres High?

The observed relay tower stood roughly 20 metres tall.

Although the exact design height depends on the venue, several engineering considerations influence this decision.

A higher loudspeaker position allows sound to travel over the audience rather than being absorbed by thousands of people standing between the tower and the listening area.

Additional height also improves coverage uniformity and reduces acoustic shadowing.

At the same time, increasing height also increases wind loading and structural demands.

The final tower height therefore represents a balance between acoustic performance and structural safety.

Engineering Observation: Why Was This Tower Built This Way?

One of the most interesting aspects of this project was not the loudspeakers themselves, but the engineering decisions behind the supporting structure.

Each visible component appeared to serve a specific purpose.

A Steel Top Section Supports Heavy Suspended Loads

The loudspeaker array was suspended from a black steel top section.

Compared with aluminium, steel provides higher stiffness and better resistance to concentrated suspended loads.

Using steel in this area helps reduce local deformation where the loudspeaker rigging connects to the structure.

The Main Mast Used Heavy-Duty Aluminium Truss

Instead of building the entire tower from steel, the main vertical mast consisted of heavy-duty aluminium pin-connected trusses.

This significantly reduces transportation weight while allowing faster manual assembly on site.

Using aluminium for the largest structural section improves installation efficiency without sacrificing the required structural capacity.

This combination of steel and aluminium demonstrates a practical engineering trade-off rather than a preference for one material over another. Similar material selection principles can also be found in many Truss System designs used for temporary event structures.

Eight Diagonal Braces Increased Structural Rigidity

The aluminium mast was connected to the steel base by eight diagonal braces.

Rather than supporting vertical loads, these braces appeared to improve overall rigidity by reducing lateral movement and torsional deformation.

Temporary outdoor structures are subjected not only to gravity but also to wind-induced forces.

Increasing the number of diagonal members helps distribute these forces throughout the structure.

Four Water Tanks Provided Temporary Ballast

One of the most distinctive features of the tower was the use of four large water tanks positioned symmetrically around the base.

Instead of transporting several tonnes of steel or concrete ballast, the tanks can be delivered empty and filled with water after installation.

This approach greatly reduces transportation weight while still providing substantial resistance against overturning.

Water ballast has therefore become a common solution for many temporary outdoor event structures.

Guy Wires Improved Overall Stability

Guy wires extended from the top section toward the four ballast positions.

Rather than allowing the tower to resist every bending force through the mast alone, the guy wires transferred part of these forces into tensile loads anchored by the water ballast.

This significantly improves overall stability while reducing structural movement under wind loading.

Extended Steel Outriggers Increased the Stability Footprint

The water tanks were not placed directly beside the tower.

Instead, they rested on extended steel outriggers bolted to the primary base frame.

Increasing the distance between the ballast and the centre of the tower increases resistance to overturning.

The symmetrical arrangement also helps distribute forces more evenly under changing wind directions.

Adjustable Leveling Feet Created a Stable Foundation

The steel base incorporated multiple adjustable leveling feet.

Although easily overlooked, these components are essential.

Outdoor event sites rarely provide perfectly level ground.

Adjustable feet allow installers to level the structure before the tower is fully loaded, ensuring that vertical loads are shared correctly across the entire base.

Why Was the Entire Tower Black?

Another noticeable feature was the tower's black finish.

This choice is not simply aesthetic.

Black structures are generally less visually distracting during concerts, especially under stage lighting and television cameras.

By reducing reflections and blending into darker backgrounds, the towers become less noticeable to spectators while allowing the performance itself to remain the visual focus.

Temporary Structures Still Require Permanent Engineering Principles

Although relay towers are temporary installations, their engineering principles are anything but temporary.

The tower observed during this project demonstrated several recurring design concepts:

• Heavy steel components concentrated where strength is most critical.

• Aluminium used to reduce transportation and installation weight.

• Diagonal bracing used to improve rigidity.

• Water ballast providing efficient temporary counterweight.

• Guy wires transferring wind loads into anchored tension.

• Extended outriggers increasing resistance to overturning.

• Adjustable feet ensuring stable load distribution on uneven ground.

Each decision represents a balance between safety, efficiency, transportation and construction practicality.

Conclusion

To most concertgoers, relay speaker towers appear to be simple structures holding additional loudspeakers.

In reality, they are carefully engineered temporary support systems designed to solve both acoustic and structural challenges.

Acoustically, they extend consistent sound coverage across large venues.

Structurally, they combine steel, aluminium, ballast, guy wires and bracing into a stable system capable of supporting heavy suspended loads in outdoor environments.

By understanding why these towers exist and how they are constructed, we begin to appreciate that successful concert engineering depends not only on spectacular performances, but also on countless carefully considered structural decisions working quietly in the background.