A Second Look at 4Silence, an EIC Accelerator Winner on Road Noise

Most noise barriers work by being tall. 4Silence, a spin-off of the University of Twente in Enschede, sells barriers about one metre high that rely instead on a row of grooves of different depths, which make passing sound resonate and bend upward over the houses behind. In January 2019 it was one of the first winners of the European Commission's revamped SME support, selected in the 9 January cut-off of the EIC SME Instrument Phase 2, the forerunner of today's EIC Accelerator, according to the Commission's list of winners. The project, WHISSPER, received an EU contribution of €2,159,500 towards a total cost of €3,085,000, according to CORDIS.

Seven years later the company is still trading and still installing. In June 2026 it reported 200 metres of its WHISwall at the Höllberg rest area on the A8 motorway for Die Autobahn GmbH des Bundes, Germany's federal motorway company, according to its project page. In March 2025 the engineering group Demcon took over the company's acoustic measurement device and consultancy work, leaving 4Silence with the noise reduction products, according to Demcon.

What 4Silence Is Doing Now

The company's website lists six products and a run of installations published since 2024: 140 metres of WHISwall in Euskirchen, 200 metres of WHISstone in Wezep, a WHIStop on the A620 motorway in Saarbrücken commissioned by Autobahn GmbH, more than half a kilometre of WHIStop and WHISwall along the L178n in Merseburg for the roads authority of Saxony-Anhalt, nearly 300 metres of WHISbarrier in Vreeland for the Province of Utrecht, and the Höllberg wall, according to its projects pages. It has also fitted 800 vibration-damping plates to the Coenbrug, a steel bridge in Zaanstad, with Rijkswaterstaat. These are company statements; the clients have not published their own accounts of the projects that could be found, apart from the measurement programmes described below.

Both Dutch registers that publish free data show filings continuing. North Data lists balance sheets of 4Silence B.V. (KvK 74934503) for every year from 2022 to 2025, the last filed on 16 June 2026, according to North Data; the figures themselves sit behind a paywall and could not be checked. Oozo, which republishes Chamber of Commerce data, lists the company as active at Vliegveldstraat 174 with one working person registered, according to Oozo. That figure counts only those registered at this entity and does not match the seven people named on the company's team page.

Two Companies Called 4Silence

The register shows more change than the website. The company the University of Twente describes as founded around Wijnant's 2009 patent, according to the university, was registered in October 2012 as 4Silence B.V. under KvK number 56184581, according to OpenCorporates and Oozo. That entity is now called DEMCON sound solutions B.V. and sits at Institutenweg 40 in Enschede with 2 to 5 staff, according to Oozo and North Data. A second company, today's 4Silence B.V. (KvK 74934503), was incorporated in May 2019, the month the EU grant was signed; OpenCorporates still lists it as 4Silence Nederland B.V., while North Data and Oozo give its current name as 4Silence B.V.

Demcon said it had "partially acquired Sound Solutions Holding", carving out the Sonocat measurement sphere and the consultancy, and that Wijnant joined Demcon sound solutions as founder and co-shareholder, with Demcon's Joost Mulder as managing director. Wijnant is listed as senior acoustic scientist on Demcon sound solutions' team page, and he no longer appears in the 4Silence team list. Which of the two entities signed the EU grant agreement cannot be established from free public records: CORDIS gives only the name "4SILENCE BV" and the address Vliegveldstraat 100 C 38, which OpenCorporates records as the head office address of both companies. Two foundations that hold shares for certificate holders, Stichting Administratiekantoor 4Silence (November 2022) and Stichting Administratiekantoor 4Silence Werknemers (January 2024), were also registered, according to Oozo; the names suggest an employee share scheme, but the shareholdings are not public.

The Technology: Bending Sound Instead of Blocking It

Conventional measures either block road noise with a wall, usually around three metres high, or absorb it with porous asphalt. A diffractor is a strip of grooves of different depths, each tuned to a band of traffic noise frequencies. Sound skimming along the surface enters the grooves and resonates, and the resonance pushes the passing sound waves upward, leaving a quieter zone behind, as the company's website and the WHISSPER report describe it. The product family applies the principle in different places: WHISstone is a grooved concrete kerb at road level, WHISwall a one-metre concrete wall with a weathering steel diffractor on top, and WHIStop an aluminium add-on for existing barriers that the company says adds 4 to 5 dB, which it compares with raising the barrier by 2 metres.

The claims have been tested by public bodies, and the results are lower than the marketing in some cases. Germany's Federal Highway Research Institute (BASt) measured WHISstone at 1.6 dB for controlled pass-bys at the Enschede test site and 2.3 dB at the front lower microphone on the B25 near Nördlingen in September 2021, and a WHISwall at 4.7 dB more than a wall of the same height without the diffractor, according to a BASt poster. The company quotes 2.2 dB for one row of WHISstone on its product page and gave about 2.5 dB in 2020, according to Innovation Origins. Its 7 to 9 dB figure for WHISwall, quoted on its Euskirchen page, is measured against a different baseline and cannot be compared directly with the BASt result.

The add-on for existing barriers has since been measured in Ireland as well. Transport Infrastructure Ireland had a WHIStop fitted in April 2024 to a new 3-metre timber barrier on a motorway in the west of Ireland, and researchers at the University of Galway found levels behind the section with the WHIStop "approximately 2dB" lower on average than behind the bare barrier, against the 4 to 5 dB the company quotes, according to their paper for the Forum Acusticum 2025 conference. The authors said a larger drop at the farther of their two measuring points could not be put down to the WHIStop alone, and that traffic differed between the measurement periods. An earlier paper by W. Bartolomäus and F. Strigari on diffractors in the journal Lärmbekämpfung reported "approximately 2 dB" for diffractors set into the ground and a weaker effect for trucks than for cars, according to its TRID abstract.

What WHISSPER Promised, and What CORDIS Shows

The grant was signed on 9 May 2019 and the project ran from 1 June 2019 to 31 March 2022. 4Silence BV is the only beneficiary listed on CORDIS and the only one named for the project in the Commission's list. The objective was to make the products ready for production at scale and to win acceptance from road and rail authorities across Europe, through six pilot demonstrations and inclusion in national noise calculation models. The final periodic report lists what was achieved: optimised production, four pilots, a test facility in Enschede where authorities could measure in a controlled setting, and sales partners in Belgium, the UK, France and Denmark.

The pilots took place in Belgium, where the Flemish road authority and the Belgian Road Research Centre installed 150 metres of WHISwall on the N445 near Zele and measured an average 10 dB reduction; in Germany with Deutsche Bahn under its I-LENA rail noise programme and with BASt on roads; and in Denmark near Vallensbæk, according to the report. The Commission's results article says the project met its goals "despite some delay due to the COVID pandemic". The report also says the company tried to make WHISstone from self-compacting concrete and dropped the idea as "very expensive with very limited advantages".

1. Production ready to scaleDeliveredProduction methods optimised, per the CORDIS report; WHISwall installed at 200 m in two days at Höllberg in 2026.
2. Six pilot demonstrationsPartlyFour pilots plus a test facility, per CORDIS.
3. Dutch calculation modelDelivered, latePromised for April 2022; a rule for a diffractor on a screen went to public consultation on 29 June 2022 and is recorded as in force.
4. German approvalPartlyBASt approval for roads is a company statement; BASt measured and accompanied pilots. Deutsche Bahn's planned addition of diffraction to its Schall 03 model could not be verified.
5. French calculation modelNot achievedThe company's calculation page still shows the French software module as "coming soon" in 2026.

What 4Silence Has Achieved Since the Award

The clearest gain is regulatory. In the Netherlands, WHISstone entered the official calculation rules on 1 January 2020, according to Innovation Origins, and the Ministry of Infrastructure and Water Management proposed adding a calculation rule for a diffractor placed on a noise barrier, along roads and railways, based on a TNO report on the WHISwall, according to the explanatory note. The same note adds a caveat: too little was known about the cost of a diffractor on a screen to include it in the annex used to judge whether noise measures are cost-effective. That matters, because the company sells mainly on cost, claiming savings of "approximately 50%" over traditional solutions on its home page.

In Germany, BASt ran a measurement programme on WHISstone and WHIStop, with a WHIStop retrofit planned on the A45 near Salingen in 2022 and on the A620 in Saarbrücken in 2023, according to the BASt poster; the Saarbrücken installation appears on the company's project page in July 2025. In the UK, Innovate UK paid £265,373 between June 2019 and March 2020 to field-test the WHISwall in a railway setting, according to UKRI, and a 120-metre WHISwall was installed at Chorleywood station for Transport for London in January 2020, according to Open Access Government and the company's London page. The founders won the University of Twente's 2021 Van den Kroonenberg Award for entrepreneurship, and the company lists further prizes, including the 2023 DEGA Lärmschutzpreis of the German acoustics society.

The pilot stage has not yet turned into the kilometre-scale contracts the founders described. In December 2021 the company had 10 employees and was discussing deployment "across kilometers" in England pending feasibility studies, according to Innovation Origins. The named projects published since are measured in hundreds of metres, and no English contract of that size has been announced. The project page for Ennis in Ireland gives the length as both 150 metres and 100 metres.

The Money

Why Europe Should Care

Road traffic is Europe's largest source of harmful environmental noise. About 92 million people are exposed to harmful day-evening-night levels from road traffic, according to the European Environment Agency, and the EU's Zero Pollution Action Plan targets a 30% cut in the share of people chronically disturbed by transport noise by 2030, according to the European Commission. The Commission also notes there is no binding EU reduction objective, so the market depends on national and regional road and rail authorities and their calculation rules. That makes 4Silence's slow work on the Dutch and German rule books the real test of the technology: a product that cannot be modelled cannot be specified in a tender.

The Verdict

4Silence has not been asked for comment for this article. It is based entirely on public records, company statements and EU project data, linked throughout.