3D warp-knitted textiles – a new dimension in sound insulation
Acoustic spacer textiles reduce noise levels and provide a textile feel and an attractive design
Noise is frequently irritating and has a negative effect on the nervous system, on comfort and on work performance. At a level of just 40 decibels, which corresponds to low radio noise, concentration can be reduced by 20-30%. /1/
Sound-absorbing ceilings, partitions, floors and furniture surfaces can reduce disruptive noises, and are a promising application for materials having acoustic properties. It is estimated that there are roughly 3.2 million square metres of new office space alone in Germany.
Examples of conventional ways of reducing noise inside buildings include the use of pressed mineral wool or MDF sheets in ceilings, non-load-bearing partitions made from mineral wool or plasterboard, textile-covered flat pressed boards as mobile interior walls, and polystyrene in various applications - a whole range of systems that have now been complemented by a new solution made solely from textiles. This new innovation features room elements made from warp-knitted spacer textiles and was developed at KARL MAYER. The product developers at this textile machinery building company were assisted in their work by acoustic specialists at the Fraunhofer Institut für Bauphysik, IBP (Fraunhofer Institute for Building Physics).
Principles of noise reduction
In order to reduce noise levels, sound should be both damped and absorbed.
Acoustic damping specifies how effectively noise from the air or a body is reflected at the surface and thus prevented from spreading. It is characterised by the degree of sound reflection.
With sound absorption, the sound energy is converted into other energy forms and is thus reduced. In this case, the main factor is dissipation – the transformation into thermal energy by friction, for example. The characteristic parameter for noise absorption is the degree of sound absorption.
Materials that are to be used as soundproofing materials must exhibit a high level of reflection and absorption.
General design parameters and their influence on the acoustic behaviour
The acoustic characteristics of spacer textiles can be modified specifically, in which case, the main parameters are their thickness and surface construction. Whereas the cover faces, with their specific microscopic roughness, are mainly responsible for reflecting the sound waves, dissipation or absorption occurs primarily in the spacer layer.
Extensive measurements were carried out at the IBP on various 3D warp-knitted textiles in a kundtschen pipe in order to determine the influence of the design parameters on noise reduction. Spacer textiles comprising multi- and monofilament yarns in the pile, with open, dense, stretch and non-stretch surfaces having thicknesses of 10 to 52 mm were used in the experiments.
As well as studying the empirical evidence, the researchers in Stuttgart also carried out mathematical calculations. In this case, the conditions occurring in the spacer textiles under the influence of sound were transferred to the calculation model, "layering of porous absorbers", and sound propagation in the cover faces was simulated theoretically. Subsequent study of the correlation between the measured and calculated results proved to be positive.
Determining the acoustic behaviour of spacer textiles shows a correlation between the dissipation behaviour and the thickness of the textile layer in the higher frequency range. Thicker spacer textiles are preferred for high-frequency sound waves. There is also a correlation between the density of the surface and the degree of sound absorption.
Textiles having a relatively dense surface are ideal for reducing noise levels since, on the one hand, they exhibit a high flow resistance, and therefore provide good damping due to viscous friction and, on the other hand, they reflect many of the impinging sound waves.
Applications
When designed appropriately, these acoustic textiles have the same absorption spectra as similar materials and can prove effective in a range of interior design solutions. For example, they can be used in false ceilings, wall cladding, absorbent sound barriers with a soundproofing intermediate layer, and chair padding on top of solid seat shells. When using 3D warp-knitted textiles, there must be a specific distance between the cover faces when they are to be used as a single component in an entire acoustic room system or in soundproofing applications.
In addition to the applications in soundproofing systems already mentioned, the spacer textiles can also be used as stand-alone systems in rooms. For example, they can be used as acoustic sails or panels, which are suspended in a room, and are known as baffles.
Spacer textiles offer many design opportunities for reducing noise levels and they can be designed so that they have sound-transparent characteristics – a feature that is particularly useful when used in seating for concert halls.
Advantages of spacer textiles compared to conventional materials
It is not only possible to modify the acoustic characteristics of spacer textiles, they can also be used as interior design elements. For example, the flexible construction of spacer textiles enables them to be used to produce curved and arched shapes, and their textile characteristics enable soft surfaces with a pleasant handle to be produced. Furthermore, the average weight of spacer textiles is roughly 2 kg/m2, so that they are classed as lightweight materials for the building sector.
Pile-free channels and hollow spaces having specific uses can also be incorporated into the textile substrate – for example, as articulating points to produce a variety of shapes, to fix supporting elements in place, or for carrying optical elements such as light rods. Optical lighting effects can also be produced by using diodes. In this case, conductive yarns are incorporated into the textile substrate during the warp knitting process and subsequently connected to electrical components.
Practical example: design of the stand at the fair
In order to demonstrate the potential of textiles to reduce noise levels inside buildings, KARL MAYER decided to design its stand at this year’s Techtextil trade fair using elements made from spacer textiles (Fig. 8) – a challenging application in view of the high noise levels. The layout of the stand also made huge demands of the design. To attract the attention of the visitors to this innovative design, the flexible, comparatively lightweight 3D textile was worked to produce a futuristic, soundproof tunnel and a circular meeting room with an entrance resembling a snail shell. The integrated diodes and illuminated cabling in the pile-free zones supported these futuristic shapes effectively. The continuous channels were also used to hold the rods and struts of the supporting frame.
The main attraction of the spacer textile, which was 35 mm thick and had a dense surface, was to reduce noise levels. The spacer was made from polyester, had a stable IXI construction in the spacer zone, and contained electrically conductive yarns.
KARL MAYER’s design concept of the exhibition stand at Techtextil 2013 was very convincing. There was a busy through-going traffic in the room elements of the exhibition stand, where the guests could convince themselves of the sound absorbent effect of the warp-knitted spacer fabrics. Moreover, the trade press has also taken up this innovative topic.