Noise barrier

Noise barriers and noise barriers are used (eg, roads, railways, factories ) to insulate noise emanating from a linear or two-dimensional sound source, so that in a protected immission (eg residential areas, hospitals ) of the noise is so far weakened, that the statutory limits are respected. These can be measures of passive noise protection (eg, sound-proof windows ) are supplemented.

History

The first noise barriers were built in the mid 20th century in the United States due to the rise of motor transport. In the late 1960s, began to describe the acoustic phenomena in the context of noise barriers using mathematical methods and thus to determine the effectiveness. This enabled better planning of new projects.

The Noise Pollution and Abatement Act, a regulation was created in 1972, which required the construction of noise protection measures to protect people.

In order to protect the population from Lärmimissionen, noise control measures are required due to the Federal Pollution Control Act in excess of the statutory guideline, if the sound source is too strong. Affected residents can claim appropriate expertise or noise emission forecasts in their community.

Often, noise barriers will be installed along railway tracks. In 2007, a total of 35 km of noise barriers were erected in the area of ​​Deutsche Bahn.

For sound insulation of railway lines low noise walls are a newer innovation. Because of their mode of action are low, less than 50 cm high walls, which are mounted directly next to the tracks, as effective as high, more distant, traditional walls. Possible, such a noise, because the majority is caused by noise in rail traffic from the wheels (vibrations, curve squeal, etc.).

Mode of action of noise protection walls and ramparts

Noise barriers have a lärmabschirmende effect, ie they partially prevent the spread of the sound. In this way, noise reductions of up to 20 dB ( A) can be achieved. The effectiveness of a noise barrier as a noise barrier depends on the following factors:

  • Height of the noise barrier
  • Acoustic design of noise barrier
  • Distance from the noise source ( place of issue )
  • Distance from the immission
  • Height of immission
  • Frequency spectrum of the sound
  • Curvature of the wall

In addition, the following factors influence the insulation effect:

  • Reflections on opposite buildings or an opposing noise barrier can reduce the noise insulation. The reflected sound impinges at a shallower angle to the wall or dam, so that the insulating effect is not as big by sound scattering. In addition, the reflected sound is added to the direct sound.
  • Reflections on the ground can reduce the insulation effect. On the immission sound level is affected not only by the direct sound on the wall or dam, but also through ground waves which run along, for example, on the surface. Is the floor sound- hard ( eg asphalt ), the bump may well spread and increase the level. Is the floor sound absorbing (eg, forest floor ) hardly ground waves can propagate; the level can thereby be reduced.
  • Weather conditions (wind, temperature stratification ) can break the sound waves upward or downward.
  • The sound path between source and receiver around the obstacle is longer than the direct path, because the sound waves have to take a detour on the wall or dam. This leads to a gain reduction due to the distance law.
  • Diffraction effects at the top reduce the effectiveness. The sound waves that hit the wall or dam are diffracted at this. This achieves the sound partly immission that are hidden behind the wall. Immission that reaches a receiver after the crossing of the crown, in this case depends on the angle through which the sound is deflected at the moment. The angle of diffraction depends on the frequency, and is the smaller, the higher the frequency. A simple model to account for these effects was presented in 1968 by Meakawa (→ see acoustic shadow ).

Variants

Sound insulation walls are made in a variety of materials and shapes. For a good mode of action are sound-absorbing materials are of advantage as they reflected and penetrating sound reduction especially. These are especially porous materials, such as plastic.

Another crucial factor is the durability. The materials should have a long life and resist the weather. For applications in the railway sector is also to be taken into account that large pressure differences caused by passing high speed trains.

The different shape and design have primarily aesthetic reasons. But special bends or special upper edge forms may also contribute massively to increase efficiency.

Various methods of construction with materials are:

  • Concrete walls are mainly used because of their great durability.
  • Metals such as steel and aluminum are often used.
  • Wood has a much shorter shelf life, but it is considered better in the landscape eingliederbar.
  • Glass is used mainly for aesthetic reasons. Window in the wall to break up the monotony and for the motorist.
  • Gabions find more and more applications in noise.
  • Plastic such as PVC or porous materials are used because of their good sound insulating properties.
  • Noise barriers can be built directly from the excavation during road construction and they can be inserted with planting well into the landscape. However, their effectiveness ( reducing sound levels to height) is lower than in walls generally and the space requirement is enormous.

Noise protection wall on a highway

Noise barrier made ​​of concrete elements at the railway high-speed line Ingolstadt -Nürnberg

Noise components at the A 96 near Landsberg am Lech

Noise barrier made ​​from renewable raw materials

S -Bahn noise barrier in Olching ⊙ 48.21145511.330112

BAB 9 in Munich

Sound Screen Improvers

In Sound Screen Improvers ( SSI) are devices that are used to attempt to increase the efficiency of noise barriers. In general, the cylindrical or prismafömige objects that are attached to the upper edge of the wall. Due to the use of absorbent materials and their rounded shape ( in contrast to the sharp edge ) diffraction effects are reduced and thus a larger space protected behind the wall in front of the sound waves. Measurements of the ÖBB on a test track showed reductions in the sound level of 1.5 dB ( A) to 5.5 dB (A ) compared to the original state.

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