Why Mechanical Systems Are a Common Source of Noise
A rooftop air handling unit (AHU) starts up and vibrates as it operates. But that vibration doesn’t stay on the roof. It travels directly into the building’s steel and concrete structure. Once this energy enters beams, slabs, and columns, the building itself becomes a pathway for sound, radiating low-frequency noise and rumble into occupied spaces far from the source, sometimes ten floors away.
This type of structure-borne noise is common in hospitals, data centers, and other facilities with large mechanical systems running continuously. Because the noise is carried through the structure rather than the air, traditional acoustic treatments often fail. This article explains how structure-borne noise works, why mechanical systems are frequent culprits, and how engineers control vibration at the source to stop it from spreading through the building.
What is structure-borne noise?
Structure-borne noise begins as vibration. When mechanical equipment like air handlers, pumps, or generators operate, they produce movement. If that equipment is rigidly connected to the building, those vibrations enter structural elements (slabs, beams, columns, and decking) turning the building frame into a transmission path.
Once vibration is in the structure, it can cause surfaces to radiate sound into adjacent spaces. In other words, the floor, wall, or ceiling itself becomes the speaker. Occupants may hear a low hum or feel a persistent rumble, even though the equipment generating it is far away.
This differs from airborne noise, which travels through the air and can often be reduced with barriers, insulation, or acoustic panels. Structure-borne noise travels through solid materials, making it more difficult to interrupt. Low-frequency vibrations are especially problematic because they lose very little energy as they move through steel and concrete, allowing them to travel long distances with minimal reduction, sometimes impacting spaces far removed from the source.
Structure-borne noise turns your building’s structure into a conduit for vibration, allowing low-frequency energy to travel far beyond its source and radiate sound where you least expect it.
What are common sources of structure-borne noise?
Structure-borne noise often starts with the equipment that keeps a building running. Mechanical systems such as rooftop AHUs, pumps, chillers, cooling towers, and generators produce vibration as part of normal operation. When these systems are rigidly connected to the building structure, bolted directly to roof curbs, equipment rails, or steel framing, that vibration is easily transmitted into slabs, beams, and columns.
Noise can also travel through distribution systems like piping, ductwork, and cable trays, which act as highways carrying vibration throughout the building. The difference between rigid connections and isolated mounts is critical. Equipment mounted on vibration isolators or pads absorbs and dampens motion at the source, preventing energy from entering the structure. Without these isolators, even relatively small machines can create rumbles that travel floors away.
Rigid connections let vibration travel freely through a building, while properly isolated mounts stop structure-borne noise at its source.
Why is structure-borne noise hard to fix?
Structure-borne noise is notoriously difficult to control because low-frequency vibrations travel long distances through steel and concrete with minimal energy loss. Unlike airborne sound, these frequencies are less affected by walls, ceilings, or interior acoustic panels, meaning treating the room alone rarely solves the problem. Retrofits add another layer of complexity because modifying existing structures, equipment, or distribution systems often requires careful planning to avoid inadvertently creating new vibration paths. Successful solutions demand close coordination between structural, mechanical, and power systems, which can be challenging in buildings with multiple stakeholders.
Common mistakes to avoid:
- Hard-mounting equipment that should be isolated
- Treating rooms instead of addressing the vibration source
- Ignoring vibration traveling through piping or ductwork
Because of these challenges, effective control requires targeting the source of vibration and designing solutions that account for the building as a complete system.
Structure-borne noise is hard to fix because low-frequency vibrations travel easily through structures, and treating spaces instead of sources or ignoring mechanical paths often leaves the problem unresolved.
What are the health and performance impacts?
According to the Centers for Disease Control and Prevention (CDC), an estimated 22 million workers face potentially harmful noise exposure on the job each year. Research from the CDC and NIOSH shows that prolonged exposure to elevated noise levels increases stress, fatigue, and risk of hearing issues, while the World Health Organization has linked environmental noise to cardiovascular strain and cognitive impairment. In hospitals, low-frequency vibration and rumble can disrupt patient sleep, slowing recovery and impacting overall well-being. In control rooms, data centers, and other high-focus environments, persistent vibration and low-level noise contribute to fatigue, reduce alertness, and impair decision-making, making even small disturbances a serious operational concern.
Even low-level, structure-borne noise can disrupt sleep, increase stress, and impair focus, making it a serious health and performance risk.
How can engineers control structure-borne noise?
Controlling structure-borne noise requires a systems-level approach that targets vibration at its source, interrupts its path, and ensures the building’s mechanical and structural systems work together.
- Vibration Isolation at the Source
Engineers start by isolating vibrating equipment before it can transmit energy into the building. Solutions include spring isolators, roof curbs, neoprene pads, inertia bases, and floating slabs. Selection depends on equipment weight, operating speed, and the stiffness of the supporting structure, ensuring the isolation method is optimized for the specific load and frequency. - Break the Vibration Path
Once vibration enters distribution systems, it can travel far. Flexible duct connectors, pipe expansion joints, and isolated hangers interrupt these paths, preventing energy from radiating through ceilings, walls, and floors. - Structural Coordination
Even with isolated equipment, structural interfaces play a major role. Engineers evaluate roof curbs, load distribution, separation joints, and damping strategies to prevent unintended vibration transfer between building elements. - Coordinate HVAC & Power Systems
Noise control also requires careful integration with mechanical and electrical systems. Factors such as fan selection, variable-speed impacts, redundancy planning, and generator enclosures are carefully coordinated to minimize vibration while maintaining performance and reliability. - Measure and Verify Performance
Finally, engineers verify results with field vibration testing, sound measurements, and frequency analysis. Post-installation verification ensures the solution performs as designed and confirms that low-frequency energy is properly controlled before it becomes a nuisance.
Effective structure-borne noise control combines isolating vibration at the source, interrupting transmission paths, coordinating building systems, and verifying performance to stop disturbances before they reach occupants.
How can Ketchum & Walton help mitigate structure born noise?
Ketchum & Walton approaches structure-borne noise as an engineering challenge, applying a systematic process to understand and control vibration throughout a building. The team begins by evaluating vibration sources and reviewing equipment mounting conditions, then analyzes how energy travels through structural elements and distribution systems. Based on these insights, Ketchum & Walton recommends appropriate isolation strategies and coordinates solutions with HVAC, generator, and other building systems. Their involvement continues through commissioning and verification, ensuring that the installed measures perform as intended and that vibration is effectively managed across the facility.
Ready to stop structure-borne noise at its source? Contact us today to have our engineers evaluate your building, recommend solutions, and ensure a quieter, more comfortable environment.