Solving traffic noise through diffraction

Besides absorbing, preventing, or redirecting noise, 4Silence has developed an extra measure to reduce noise pollution: deflecting sound. This method is called diffraction, and with it we achieve a 9 dB reduction in noise from the adjacent road. This we do with the WHIS®stone, WHIS®wall & WHIS®top.

The principle gives our products many benefits compared to other solutions:

  • they leave views intact;
  • they’re cheaper;
  • and they’re simple and fast to install;
  • they can also easily achieve much extra noise reduction in existing situations.


This concrete diffractor is 1 meter wide, and is placed directly next to the road at ground level, realizing a 2.5 dB noise reduction, equal to silent asphalt. Even 5 dB is possible when using a double row.

Its big advantage is that the noise reducing effect remains the same throughout its whole life span (30 years), unlike silent asphalt, which reduces 0.5 dB less every year.

The WHIS®stone is perfect for provincial roads and distributor roads. It’s safe to drive across.



The WHIS®wall combines the advantages of a low noise barrier with a diffractor. Together, the weathering steel diffractor and the custom made substructure are 1 meter high, achieving a 9 dB reduction for the adjacent lane. Even for farther away lanes the WHIS®wall still realizes a 7.5 dB reduction. The WHIS®wall can be applied next to any kind of road.



The WHIS®top is a lightweight aluminum diffractor that can be mounted on most existing noise barriers. An ideal cheap solution in cases where extra reduction is required.

The WHIS®top adds an additional 4 to 5 dB reduction, comparable to what you’d achieve by raising a regular barrier by 2 meters.

The WHIS®top is beneficial because it barely adds any weight or wind load, so existing constructions don’t need to be weighted and new ones can be carried out lighter.


Diffractie is recognised by law as a noise reducing measure

Rijkswaterstaat and several provinces were closely involved in validating our products for applications alongside railroads. They’re part of the reason our products have been admitted into the measurement and calculation requirements for 2012 per January 1, 2020. So they’re approved for application.

Internationally renowned

Meanwhile 4Silence has been busy abroad, leading to our products being acknowledged by the following parties:

For more information or a non-binding telephone consultation: