Parametrically Optimized Lightweight Acoustic Absorber
Based on an idea by Anke Eckardt, the POLA research project centers on the development of a new system for the attenuation of low-midrange and bass frequencies, featuring lightweight unitized construction customizable to any indoor or outdoor location.
The system combines two seemingly dissimilar materials: air, a sound-propagating medium that also happens to be the mixture of gases in the atmosphere (1 m³ = 1.293 kg) and (U)HPC, or (ultra) high-performance concrete, a lightweight concrete composite with a refined aesthetic. This marriage of sculpture and function is the fundamental idea behind POLA.
To create this novel soundproofing system, the POLA project combines the functionality of a Helmholtz resonator with a new development in the field of engineered concrete. By acoustically optimizing the surfaces of textile-sheathed (U)HPC, the resulting resonance absorber can be made to cover the necessary bandwidth. This system owes its unique effectiveness to an inventive method of creating acoustic macro- and microstructures:
• Macrostructuring A number of resonance absorbers tuned to varying frequencies are parametrically combined so that their overlapping bandwidths produce the broad sound spectrum necessary for effective noise reduction. Together, the resonators that make up the component form a site-specific sound-absorption structure (= macrostructure) in the form of an irregular honeycomb. The size and distribution of the cells is calculated on the basis of site-specific measurements and integrated into construction by means of an innovative concrete-forming system. The honeycomb structure is not only highly acoustically functional but also performs extremely well in the critical area of wind load resistance (both positive and negative).
• Microstructuring The cell structures are built from a new type of acoustically optimized open-pore (U)HPC that is engineered to have a low Q factor (quality factor) and thus a high bandwidth. While (U)HPC has exceptional structural qualities, its surface is typically very smooth, making it a poor material for noise abatement. A method developed by Building Art Invention and incorporated into the forming process has made it possible for the first time to produce (U)HPC with a highly porous, acoustically optimized surface; this method is used on the insides of the absorbers.
The POLA system is a self-supporting element; thanks to its unitary construction and freedom from external supports, it is an ideal material not only for building interiors and facades, but also for noise barriers along highways and high-speed rail lines, where it can withstand the extreme wind loads produced by passing traffic.
The combination of air and concrete produces hollow cavities, each of which has a volume. Being a three-dimensional object, an air-filled natural cavity can serve as sculptural material. The myriad combinations of volumes and shapes gives rise to an inexhaustible array of forms in space. With the addition of openings, these forms can be made to produce a variety of “tunings” like those used in the long tradition of musical-instrument making, “coloring” the surrounding space on the auditory level and creating an aesthetically discernible SONIC SPACE.
With this blurring of the line between the artistic and the functional comes a dehierarchization or even dissolution of the art object “in favour of a vivid acoustic topography” that is experienced more as a total landscape. It is a conception of architecture “not only as an enclosure of space but as a system of thresholds regulating the repulsion, ingestion, and expulsion of environmental elements, not least of which (is) sound,” with ears that are “in a constant and productive dialogue with the walls, thresholds, and spaces” around them.(1)
(1) Niall Atkinson, “Thinking through Noise, Building toward Silence: Creating a Sound Mind and Sound Architecture in the Premodern City,” in “Acoustic Modernity,” special issue, Grey Room, no. 60 (Summer 2015): 12.