Versuchsaufbau Schalllängsleitung

Can you hear Anything?

At the HFT Stuttgart University of Applied Sciences a team of researchers headed by Johannes Weinhold has conducted a study – the first of its kind – on flanking sound transmission in wood-concrete hybrid structures. The results should facilitate acoustic design for construction planning in the future.

The status quo

The research project compiled a catalogue of components including construction details and sound parameters. Headed by construction physicist Johannes Weinhold from facade engineering at Zentrale Technik in Stuttgart, in cooperation with ZÜBLIN Timber, Elbe Decken und HFT Stuttgart, the team investigated solid timber structures such as LENO®cross laminated timber elements. These allow for a fast and cost-efficient construction of buildings; however, there currently are hardly any normative or metrological values that could be used as a basis for the acoustic design of such hybrid structures and their flanking sound transmission.

The experiment

Flanking sound transmission is differentiated into horizontal and vertical sound transmission. For their vertical and horizontal measurements, the research group applied varying loads in different experimental set-ups using hydraulic pistons and LENO cross laminated timber elements, an ELBE concrete ceiling and a LENO wall to obtain a realistic representation of sound transmission. The shocks were loaded with up to four tons. The flanking sound transmission measure Rij,w [dB] was selected as the relevant parameter for the assessment.

The result

The vertical measurement of flanking transmission shows that various acoustic decoupling measures, including elastomers or building protection mats, had only an insignificant influence on the insulation at joints between the timber wall and the reinforced concrete ceiling. Fluctuations in vertical flanking sound transmission amoun-ted to approx. four decibels and significantly depended on the superimposed load. The construction of timber walls and hollow core slab ceilings provide a very good flanking sound transmission measure in the vertical direction (approx. Rij,w = 60 dB). These high values could be confirmed by the building acoustics measurements in the existing building both for the impact sound and for the airborne sound.

The horizontal measurement showed a significantly higher dependence of flanking sound transmission on the respective structure. Various connectors for the joint, such as bolts, butt boards, continuous or screwed-on beams and butt joints, were studied. Each type of connector causes a significant decrease in the flanking sound transmission measure, which means that horizontal flanking sound transmission remains a huge challenge in solid timber construction.

Vertical joint (inside view)
Joint (front view)
Hydraulic joint pressure
Vertical joint (close-up view)

The sound

Sound waves always need a medium for propagation. They can be transmitted via air, masonry, iron or wood, which is why we can hear noises from the other side of a wall. If a trans-mission medium is missing, it is absolutely silent – as is the case in outer space, where there are almost no particles to transmit sound vibrations. If this was not the case, we would be able to hear the sound made by the helium and hydrogen flares on the sun.

The standard

The DIN 4109 standard regulates acoustic insulation between domestic living and working spaces against external noise and noises from building service installations as well as from construction-related operations. The standard also governs various procedures for the verification of sound protection.