Acoustical engineer Bernt Mikal Larsen of Multiconsult has made some new, very interesting discoveries about impact noise levels for slab-on-grade foundations | Photo: Multiconsult

New findings on impact noise can reduce costs

By using new information when calculating impact noise, developers can make big savings with respect to the floor covering or finish floor needed in buildings with a slab-on-grade foundation that have rooms where noise control is required. These findings have attracted international interest.

25. May 2021

Acoustical engineer Bernt Mikal Larsen of Multiconsult has made some new, very interesting discoveries about impact noise levels for slab-on-grade foundations. Through his calculations, he has quantified how much impact noise is spread through the ground when you split the concrete slab and layer of expanded polystyrene (EPS) into sections. This is an area that was previously little understood.

The findings will therefore make it possible to choose far more appropriate and cost-effective solutions for floor coverings and finish floors, and to choose the right solution for limiting lateral transmission of noise from machinery.

Can result in big cost-savings

The uncertainty about how impact noise spreads horizontally through slab-on-grade foundations, and the fact that this topic is not discussed in trade journals, means projects have tended to “overengineer” floor coverings and finish floors.

The new findings will therefore enable appropriate designs to be implemented immediately. This will lead to big cost-savings in terms of the quality of floor covering or finish floor actually required in buildings with slab-on-grade foundations that have rooms where noise control is required. Overengineering and excessively high standards for floor coverings will be avoided.

“The estimated values for impact noise will give suppliers of floor coverings and contractors a much firmer basis for judging what kind of finish floor is needed, allowing them to choose the right one for different kinds of buildings with different functions”, believes Larsen.

Larsen goes on to explain that it was previously assumed that all noise problems could be solved by splitting the concrete floor and the EPS layer below it into sections. His findings show this is not necessarily true, particularly in the case of machinery that emits low-frequency sound which travels from room to room through the ground.

“Designing slab-on-grade foundations correctly will be vital, for instance, in industrial buildings with machinery that emits low-frequency sound, where it may be better to use good vibration isolators than to split the concrete slab into sections.”

Lots of international interest from acoustical engineers

There is currently very little technical literature on the subject, so Larsen believes that the new findings will be very valuable for acoustical engineers both in Norway and internationally.
“Understanding the different kinds of design solutions for slab-on-grade foundations will be very useful to acoustical engineers when designing new buildings. It is also very important to the interfaces with other disciplines such as structural engineering, building physics and architecture”, explains Larsen.

Larsen’s findings about impact noise have already generated international interest, and on 4 May he gave a presentation at the Baltic-Nordic Acoustics Meeting in Oslo. Over the summer, Bernt Mikal Larsen has been invited to present his findings at a further two prestigious international conferences, namely the International Conference On Vibration Engineering, to be held in Shanghai on 24-16 July, and Internoise in Washington DC on 1-5 August. The conference in Shanghai, which is held every 4 or 5 years, is organised by universities in Beijing and Shanghai, while Internoise, which is held annually, features presentations by acoustical engineers from all over the world.

“Acoustical engineers from other countries have expressed great interest in the topic, and have said that this kind of knowledge will be very useful to future design work and the choice of appropriate solutions. Many people have wanted more information about the subject, as it is barely discussed in the technical literature. I am looking forward to participating virtually at the conferences and presenting my findings”, says Larsen.