Acoustic and washable air inlet canopy

Improved acoustic insulation and cleaning compared to standard products thanks to the use of Helmholtz resonators to treat the acoustics, instead of melamine foam

Customer : Sil vous plait, Sil&Add's product brand

Project partners : CETIAT & CSTB (standardised testing), NGI (industrialisation), Cabinet Chaillot (industrial protection)

Context

Air inlets provide fresh air for natural ventilation or single-flow ventilation systems.

Outside noise (from roads, city centers, etc.) penetrates homes through the entire envelope. When air inlets don't provide sufficient insulation, they become the weak point in insulation.

To improve the insulation of air inlets, acoustic foams are often used. These cannot be cleaned of deep pollution deposits.

The aim of this project is to develop and industrialize a new canopy (mounted on the outside of the window) that improves the acoustic insulation of the air inlet, while being easy to clean.

Blog - Acoustics of air inlets

Project

Innovation roadmap

To set a clear framework for development, we defined precise specifications: dimensions, materials, maximum cost, the need for a 100% cleanable acoustic solution.

These specifications are the result of a study of similar existing products on the market, standards and DTUs, and discussions with acoustic engineers and architects.

The product must therefore soundproof the air inlet using cleanable Helmhotz resonators that do not reduce the air flow.

Pre-study

To identify the acoustic phenomena that govern the insulation performance of air inlets, we first produced a simplified finite element numerical model (normal incidence, 2D model), which we compared with an analytical model.

This pre-study demonstrated the product's potential and why the number and position of resonators in the product are so important.

Modeling

Then we used Comsol Multiphysics to digitally model the complete acoustic problem: diffuse field, 3D model, interior and exterior accessories, porous materials and impermeable films, transmission coefficient per one-third octave band, and the standard's unique performance index. This modelling confirmed the major trends observed during the pre-study.

Conception and optimisation

The product was then convceived and optimised for :

its mechanical aspects so that it can be produced as a prototype using 3D printing;
its acoustic aspects, by optimising the geometric parameters and materials that have an impact on its insulation performance, using the complete digital model.

Prototyping and laboratory testing

Prototypes of the product were produced using 3D printing.

They were characterised in a test centre, in accordance with standard NF EN 13141-1:2019, by CETIAT, France. This laboratory competed with other laboratories and was selected for its availability, rates and COFRAC accreditation.

Industrialisation

Together with our partner, NGI, we modified the design of the product so that it could then be manufactured by plastic injection.

Plastic injection tools are made in China, then repatriated to France for production.

Small elements of the acoustic resonators are produced by 3D printing to limit investment in tooling. They can then be injected.

Final laboratory testing

The finished product, manufactured using plastic injection molding, was tested at the CSTB, a COFRAC-certified testing center, in accordance with standards NF EN ISO 10140-2, NF EN 13141-1, and NF EN ISO 717-1.

Industrial property

Working with Cabinet Chaillot, we carried out a prior art study early on in the project and filed a patent application with the INPI to protect the product.