WHIS®wall: reducing railroad noise pollution with 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 7 dB reduction in noise from the adjacent track. This we do with the WHIS®wall.

Even for the third track (12 meters away from the WHIS®wall), the WHIS®wall achieves a 5 dB noise reduction.

This method is perfect for reducing noise railway noise, because:

  • It’s considerably cheaper than other methods.
  • The view is preserved – for residents as well as travelers – because the WHIS®wall is only 1 meter high.
  • Installation is super easy, barely an inconvenience, and requires no foundation.
  • It can be supplied with earthing.
  • It’s safe – all emergency facilities were taken into account during the WHIS®wall’s development.
  • It’s placed in the same spot as a regular noise barrier, so it won’t affect railway maintenance.
Differences between WHIS®wall and small noise barriers

The WHIS®wall often gets confused with a miniature noise barrier. But there are a couple of major differences between small noise barriers and the WHIS®wall:

  • A small noise barrier is placed directly next to the track, while the WHIS®wall stands in the same spot as a standard noise barrier. That means the WHIS®wall has no extra impact on safety or railway maintenance.
  • The mini noise barrier only effectively reduces noise for the first adjacent track, NOT the second or third tracks. The WHIS®wall remains effective for tracks that are farther away.


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

Deutsche Bahn
Deutsche Bahn
Transport for London
Transport for London
Network Rail
Network Rail