Structure-borne sound

What is structure-borne sound?

Structure-borne sound refers to vibrations that propagate within solid materials such as concrete, timber, steel or masonry. When a vibration is generated – for example, by walking, a machine or an impact – it is transmitted into the structural element as a vibration and propagates through walls, ceilings or floors.

It is only when these vibrations are released back into the air elsewhere that audible noise is produced. This is why structure-borne noise is often only noticed after the fact, even though the actual source may be some distance away.

How does structure-borne noise arise?

Structure-borne noise always arises when a mechanical force acts on a solid body. Even small vibrations are sufficient for oscillations to propagate through the material.

Typical causes include:
• Footsteps on stairs or floors
• Washing machines and tumble dryers during the spin cycle
• Heat pumps and air conditioning systems
• Heating and water pipes
• Garage doors and roller shutters
• Fitness equipment
• Industrial machinery
• Lifts

The stiffer and harder a building material is, the better it can transmit vibrations.

How does structure-borne sound propagate?

Unlike airborne sound, structure-borne sound does not require a medium such as air. The vibrations travel directly through solid building components and can be transmitted across several rooms or even floors.

Transmission most commonly occurs via:
• Ceilings
• Walls
• Floor slabs
• Steel beams
• Pipes
• Timber and metal structures

As a result, it is often difficult to pinpoint the actual source of the noise.

Difference between structure-borne sound and airborne sound

Although both types of sound often occur together, they differ significantly.

In many buildings, structure-borne sound eventually turns into airborne sound. This is why noises often seem louder or appear to come from a different direction.

Is impact sound the same as structure-borne sound?

No. Impact sound is a specific type of structure-borne sound. It is caused by walking on floors or stairs and is transmitted through the building structure. All impact sound is therefore structure-borne sound – but not all structure-borne sound is caused by footsteps.

Why is structure-borne sound often particularly disruptive?

As vibrations can travel over long distances, noise often occurs in places quite different from the actual source.

Typical examples:
• The washing machine in the basement can be heard in the bedroom
• A heat pump causes vibrations in the living room
• Pipes transmit the sound of flowing water to adjoining rooms
• Fitness equipment causes vibrations in the flats below

Structure-borne sound insulation therefore plays a particularly important role in blocks of flats or buildings with technical installations.

How can structure-borne noise be reduced?

Effective structure-borne noise insulation prevents vibrations from entering the building structure in the first place. To achieve this, vibration-decoupling materials are used which absorb vibrations and significantly reduce their transmission. The earlier the sound transmission is interrupted, the greater the effect.

Proven measures include:
• Elastically decoupling machinery and appliances
• Using anti-vibration mats under washing machines or heat pumps
• Decoupling pipework with suitable mountings
• Using floating screeds
• Using elastic interlayers between building components
• Avoiding direct contact between materials

The choice of the appropriate solution always depends on weight, vibration frequency and the installation situation.

Which materials help to reduce structure-borne noise?

Materials that absorb or decouple vibrations are used for structure-borne noise insulation.

These include, amongst others:
• A composite product made from heavy foil and acoustic foam (soni COMPOSITE)
• Heavy foils (soni HEAVY)
• PE foam (soni RESIST)

The most suitable material depends on the specific application and the load.

Where does structure-borne noise occur in everyday life?

We encounter structure-borne noise more often than many people realise.

Typical examples include:
• Washing machines
• Heat pumps
• Air conditioning units
• Ventilation systems
• Fitness equipment
• DIY tools
• Speakers with powerful bass
• Garage door openers
• Stairwells
• Lifts

Even small decoupling measures can significantly reduce sound transmission.

Conclusion

Structure-borne noise is caused by vibrations in solid materials and can travel long distances within a building. As a result, noise is often heard far away from its actual source.

Targeted structure-borne sound decoupling can reduce vibrations right at their source. This improves living comfort, protects buildings from unwanted vibrations and ensures a significantly lower noise level.