II. Reduction of unwanted sounds Archives

Vegetation for noise reduction

This concerns the role vegetation can play in some contexts to reduce noise. The measurable effect of vegetation in reducing noise has been debated, yet if the layer is thick and dense, the effect can be substantial^1,2. The ground effect related to the soil substrate should be raised in this context³, as well as visual screening (cf. Visual masking) and the sound of rustling leaves (cf. Auditory masking and Effects of vegetation).

References:
¹Van Renterghem, T., Attenborough, K. & Jean, P.. Designing vegetation and tree belts along roads. In: Nilsson, M., Bengtsson, J. & Klæboe, R. (eds.) Environmental methods for transport noise reduction. Boca Raton: CRC Press (Imprint of Taylor & Francis), 2015
²Bucur, Voichita. Urban forest acoustics. Berlin: Springer, 2006.
³HOSANNA. Novel Solutions for Quieter and Greener Cities. Bandhagen: EU FP7, 2013.

High noise screens

High noise screens are approximately 1.8 m and above. These screens should be located as close to the source (or listener) as possible for optimal effect¹. The effect depends on a number of factors, where height is the main determinant². In addition to conventional usage, high noise screens can be used in a creative manner, as part of urban design solutions incorporating features like seating^3,4, water and/or vegetation^4,5.

References:
¹Forssén, J., Kropp, W. & Kihlman, T.. Introduction to traffic noise abatement. In: Nilsson, M.,Bengtsson, J. & Klæboe, R. (eds.) Environmental methods for transport noise reduction. Boca Raton: CRC Press (Imprint of Taylor & Francis), 2015.
²HOSANNA. Novel Solutions for Quieter and Greener Cities. Bandhagen: EU FP7, 2013.
³Fusaro, G., D’Alessandro, F., Baldinelli, G. & Kang, J.. Potential of a soundscape element design. Conference Paper: 17th CIRIAF National Congress, Perugia, Italy, April 6-7, 2017.
⁴Cerwén, G.. Urban soundscapes: A quasi experiment in landscape architecture. Landscape Research 41 (5), 2016, 481-494.
⁵Hellström, B., Torehammar, C., Malm, P. & Grundfelt, G. (2013). Stadens Ljud – Akustisk design & hållbar stadsutveckling [City Sounds – Acoustic design and sustainable development]. Stockholm: Exploateringskontoret, 2013.

Low noise screens

A low noise screen compensates for its lower height (up to around 1 m) by increased proximity to the noise it is screening. The effect can be substantial in some cases¹, but there are practical issues like maintenance and traffic safety to consider. Like high screens, low screens can be combined with creative solutions that incorporate water and vegetation to form part of an urban design solution.

References:
¹Defrance, J., Jean, P., Koussa, F., Van Renterghem, T., Kang, J. & Smyrnova, Y… Innovative barriers. In: Nilsson, M., Bengtsson, J. & Klæboe, R. (eds.) Environmental methods for transport noise reduction. Boca Raton: CRC Press (Imprint of Taylor & Francis), 2015.

Buildings as screens

Strategically located buildings can be used as less obvious, yet effective, noise screens, also in combination with conventional screens. Besides the height of the buildings, the shape, location and materials applied in the building are important¹. If the buildings are intended for housing, care needs to be taken to avoid sleep disturbance². Noise exposure on one side of the building can be compensated for to some extent by a quiet façade where bedrooms can be located³.

References:
¹Hellström, B., Torehammar, C., Malm, P. & Grundfelt, G. Stadens Ljud – Akustisk design & hållbar stadsutveckling [City Sounds – Acoustic design and sustainable development]. Stockholm: Exploateringskontoret, 2013.
²FHWA. The Audible Landscape: A Manual for Highway noise and land use. Cambridge, Massachusetts: Federal Highway Administration, 1976.
³de Kluizenaar, Y., Salomons, E.M., Janssen, S.A., van Lenthe, F.J., Vos, H., Zhou, H., Miedema, H.M. & Mackenbach, J.P. Urban road traffic noise and annoyance: the effect of a quiet façade. Journal of the Acoustical Society of America, 130(4), 2011, pp. 1936-1942.

Changed topography

The shaping of the landscape topography can be used to form hills, berms or strategically shielded valleys. Earth berms along major infrastructure constitute a well-known application¹. The detailing of berms in terms of shape and use of vegetation material can have a substantial effect on performance².

References:
¹MTH. Noise control earth berms: Guidelines for the use of earth berms to control highway noise. British Columbia: Ministry of Transportation and Highways, 1997.
²HOSANNA. Novel Solutions for Quieter and Greener Cities. Bandhagen: EU FP7, 2013.

Reduce source activity

This cathegory constitutes a broad number of measures that are aimed to influence the way an activity is carried out, so that noise is reduced. This might for example concern traffic speed, which can be approached from different angles. One is to enforce the rules (e.g. speed limits), an other is to find design solutions that affect certain behaviours (e.g. reduced lane size and shared space solutions). In the latter approach, a parallel can be drawn to the notion of environmental affordances¹, a term which has also been applied to sound environments².

References:
¹Gibson, J.J.. The ecological approach to visual perception. Hillsdale, New Jersey: Lawrence Erlbaum Associates, 1986.
²Thibaud, J.-P.. The Acoustic Embodiment of Social Practice. In: Karlsson, H. (ed.) Proceeding of Stockholm, Hey Listen!, June 9-13. Stockholm: The Royal Swedish Academy of Music, 1998.

Abolish certain functions

Abolition or complete transformation of functions that produce unwanted sounds, like the transformation of a car road to a walking path, can be considered. Such a development would seem likely in relation to densification and sustainable development.

References:
No references

Maintenance

Everyday maintenance of outdoor space can have negative influences on the soundscape, particularly through use of machines with combustion engines. Maintenance can be considered by landscape architects in maintenance plans, but also in design solutions¹. For instance, a meadow is less likely to result in noisy maintenance activities than a mown lawn. Maintenance may contribute qualities in the soundscape, as when hand-driven tools are used or when animals are involved.

References:
¹Cerwén, G..Fridfulla ljudlandskap? [Tranquil soundscapes?]. Tidskriften Stad. Alnarp: Movium, 2017.

Absorbing qualities of materials

The absorbing qualities of certain materials can be used to reduce the impact from sound, particularly in conjunction with unwanted source activities like roads¹. An interesting and useful example is vegetated soil, but there are also other strategies under development in collaboration with acousticians².