The increasing migration into cities leads to an increasing number of people stressed by noise. More and more people are moving into urban settings comprised of multiple noise sources and hard reflective glass and steel facades. The omnidirectional arrangement of noise sources like airborne noise or car traffic noise and their reflection on the facades neither composes urban arrangements with silent indoor areas nor comfortable quiet areas outdoor. To come up with requirements for silent areas inside and outside of buildings further design parameters have to be introduced. The facade is not only a shelter for the inside it can also provide comfort spaces outside the building. As engineers and architects we cannot change the noise source, but we can influence the impact on the surrounding urban space by controlling the reflection of noise emissions on the urban surfaces like facades. In a facade design the capability of reflecting noise can be tuned by modifying the surface. In order to come up with the acoustical needs no radical new way of facade design has to be introduced. Mainly a shift of attention to the acoustic parameters is needed. Based on acoustic measurements of basic geometry principles this research presents known facade designs and their acoustic parameters regarding the reflection capabilities and the functions in a facade.

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The representative high-rise facades of today's major cities are composing urban spaces out of glass and steel. With the reflection of one noise source on one hard reflective facade the noise level in an urban space can increase up to 3 dB. In the case of multiple reflections in a complex urban setting the level can increase up to 8 dB. Taking this effect into account, the surfaces of inner city facades have to be redesigned aiming for absorption of the sound energy. Due to the different functions of a façade, e.g. vista, light, energy and air, the complete covering of a facade in order to gain broadband absorption is not feasible. If the targeted broadband absorption is not feasible, the absorption effect can be tuned to several frequency bands in order to transform the uncomfortable noise perception into a comfortable one. During this research facade designs were developed with a focus on the acoustical effectiveness. It was demonstrated, that with a tunable acoustical facade construction, more than one frequency band can be influenced, thus achieving a comfort soundscape in an urban space.@en