What is sound diffraction?

Sound diffraction is a fundamental wave phenomenon where sound waves bend around obstacles or spread after passing through openings. This explains why you can still hear sound even when the direct path is blocked. While diffraction is a natural principle, it can also be applied in innovative ways to control traffic noise pollution.

How does a diffractor work?

Instead of building tall noise barriers that attempt to block sound completely, a diffractor uses the principle of diffraction to redirect sound waves upwards. A diffractor is designed with grooves of varying depths. When sound waves enter these grooves, the air begins to resonate:

• Deep grooves deflect the lower frequencies of traffic noise upwards.

• Shallow grooves redirect the higher frequencies.

This clever use of resonance ensures that troublesome sound waves are bent into the atmosphere, leaving the area next to the road or railway significantly quieter.

Benefits of sound diffraction

Using diffractors for noise reduction offers several advantages compared to traditional noise barriers:

• Effective noise reduction – long-lasting and measurable reductions in traffic noise.

• Minimal visual and environmental impact – no need for tall walls that obstruct views or disrupt landscapes.

• Easy integration – diffractors can be installed with little to no disruption to roads, railways, or construction processes.

• Scientifically proven – since January 2020, diffraction-based noise reduction has been officially recognized in legislation and included in the Geomilieu software for noise calculation.

From scientific principle to real-world solution

4Silence pioneered this approach in 2012, turning the concept of sound diffraction into a practical solution for road and rail noise reduction. Products like the WHIS®stone, WHIS®wall, WHIS®barrier and WHIS®top demonstrate how diffractors can replace or complement traditional noise barriers with smarter, more sustainable solutions.