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Sound barriers are an effective engineering measure for controlling noise transmission. They are mainly used in the following areas, with significant differences in noise reduction effect and structural form (fully enclosed/semi-enclosed):
1. Main application areas of sound barriers (noise reduction objects)
1. Transportation noise: This is the main application area.
Highways/urban expressways: Reduce the impact of vehicle noise (tire-road noise, engine noise) on sensitive areas along the route, such as residential areas, schools, and hospitals. Most common.
Railways (high-speed rail/conventional rail/subway/light rail): Reduce the impact of wheel-rail noise, vehicle aerodynamic noise, and whistle noise on the environment along the line, especially in densely populated areas and elevated sections.
Urban rail transit (elevated section): Same as above, alleviating noise pollution to nearby buildings.
Airport: Installed around the airport or next to the taxiway to reduce the impact of noise from aircraft takeoff, landing, taxiing and ground support equipment on surrounding communities (the application is relatively complex).
2. Industrial noise:
Noise barrier for a project of Sanyuan Environment
It is set up within the factory boundary or factory area around high-noise equipment (such as cooling towers, compressor stations, fans, pump stations, generator rooms, etc.) to reduce the spread of industrial noise to residential areas outside the factory or office and living areas inside the factory.
3. Social life noise:
Construction sites: As part of the construction enclosure, it reduces the impact of noise from construction machinery and equipment on the surrounding environment.
Large equipment/facilities: such as substations, thermal power stations, air-conditioning units and other equipment areas.
Specific places: such as open-air stadiums and entertainment venues, used to isolate noise.
2. Noise reduction of sound barriers
The noise reduction effect of a sound barrier is not a fixed value and is affected by many factors. Generally, it can reach 10 dB(A) to 25 dB(A) under ideal conditions. Key factors affecting the amount of noise reduction include:
1. Sound barrier height: The higher the barrier, the larger the sound shadow area and the better the noise reduction effect. This is the most important design parameter.
2. Length of sound barrier: The length must be long enough to cover the area to be protected and avoid diffraction at both ends affecting the effect.
3. Location of sound source and receiving point:
Height of the sound source: The higher the sound source (such as a large truck or train), the taller the barrier will need to be to effectively block it.
Height of the sound receiving point: The lower the protected point is (such as a low-rise residential building), the better the barrier effect will be.
Distance: The closer the sound receiving point is to the barrier, the better the effect is generally; the closer the sound source is to the barrier, the better the effect is also.
4. Sound barrier materials and structures:
Sound insulation (TL): The ability of the barrier panel itself to prevent sound transmission needs to be high enough (usually TL > 25 dB is required).
Sound absorption: Whether sound-absorbing material is installed on the side facing the sound source is crucial. Sound-absorbing material effectively reduces sound reflections from the barrier surface, preventing reflected waves from bypassing the top of the barrier or reaching the receiving point via other paths, significantly improving noise reduction (especially when barriers are installed on both sides of the road). Sound-absorbing barriers can achieve an additional 3-6 dB(A) reduction compared to non-absorbing barriers.
5. Frequency characteristics: Sound barriers are effective against medium and high frequency noise (>500 Hz), but less effective against low frequency noise (low frequency sound waves have longer wavelengths and are more prone to diffraction).
6. Topography: Flat, open terrain provides the best results. Reflective surfaces (such as buildings across the street) or complex terrain will reduce the effect.
7. Atmospheric conditions: Temperature gradient, wind direction and speed will affect the sound propagation path, thus affecting the actual effect.
3. The difference between fully enclosed sound barriers and semi-enclosed sound barriers
Typical range:
A well-designed highway noise barrier of appropriate height can typically reduce noise by 10-15 dB(A) at low-rise buildings immediately behind the barrier. Under very favorable conditions (e.g., high barriers and close, low-lying receiving points), this can reach 20 dB(A) or more.
Fully enclosed sound barriers (see below) theoretically offer the best noise reduction, typically reducing noise by 20 - 30 dB(A) or more, almost completely isolating internal noise (e.g. railway) from the external environment.
Summarizing the key differences
Top structure: fully enclosed with a top cover, semi-enclosed without a top cover.
Noise reduction mechanism: Fully enclosed relies on physical isolation, while semi-enclosed mainly relies on creating sound shadow areas.
Noise reduction effect: Fully enclosed is significantly better than semi-enclosed, especially in controlling top diffraction and long-distance propagation.
Cost and complexity: Fully enclosed is much more expensive than semi-enclosed.
Applicability: Semi-enclosed is more widely used and more flexible; fully enclosed is used in specific sensitive areas where noise reduction requirements are the highest and no cost is spared.
The choice between full or partial closure requires comprehensive consideration of multiple factors, including noise reduction objectives, project budget, environmental sensitivity, space limitations, ventilation and lighting requirements, and landscape impact. In actual projects, full closure is sometimes used on some sensitive sections, while partial closure is used on other sections.