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Sound barriers are an effective engineering measure for controlling noise propagation, mainly used in the following aspects, and their noise reduction effect and structural form (fully enclosed/semi-enclosed) differ significantly:
I. Main application areas of sound barriers (targets of noise reduction)
1. Transportation noise: This is the most important application area.
Highways/Urban Expressways: Reducing vehicle noise (tire-road noise, engine noise) from interfering with sensitive areas such as residential areas, schools, and hospitals along the route. This is the most common method.
Railways (high-speed rail/conventional rail/metro/light rail): Reduce the impact of wheel-rail noise, vehicle aerodynamic noise, and horn noise on the environment along the line, especially in densely populated areas and elevated sections.
Urban rail transit (elevated section): Same as above, to alleviate noise pollution to nearby buildings.
Airports: Installed around the airport or next to taxiways to reduce the impact of noise from aircraft takeoff, landing, taxiing, and ground auxiliary equipment on surrounding communities (application is relatively complex).
2. Industrial noise:
Sound barrier for a project by Sanyuan Environment
Within the factory boundary or area, measures should be taken to surround 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 noise:
Construction site: As part of the construction site enclosure, it reduces the impact of noise from construction machinery and equipment on the surrounding environment.
Large equipment/facilities: such as substations, heating stations, air conditioning units, and other equipment areas.
Specific locations: such as the area around open-air stadiums and entertainment venues, used for noise isolation.
II. Noise Reduction Amount of Sound Barriers
The noise reduction effect of a sound barrier is not a fixed value and is affected by a variety of factors, typically ranging from 10 dB(A) to 25 dB(A) under ideal conditions. Key factors affecting the noise reduction amount include:
1. Sound barrier height: The higher the height, the larger the sound shadow zone, and the better the noise reduction effect. This is the most critical design parameter.
2. Sound barrier length: The length must be long enough to cover the area to be protected and to avoid diffraction at both ends affecting the effect.
3. Location of the sound source and the receiving point:
Sound source height: The higher the sound source (such as a large truck or train), the higher the barrier needs to be to effectively block it.
Height of the sound receiving point: The lower the protected point (such as a low-rise residential building), the better the relative effect of the barrier.
Distance: The closer the sound receiving point is to the barrier, the better the effect is usually; the closer the sound source is to the barrier, the better the effect is also.
4. Sound barrier materials and structure:
Sound insulation (TL): The ability of the barrier material itself to block sound transmission, which needs to be high enough (typically TL > 25 dB).
Sound absorption performance: Whether or not sound-absorbing materials are installed on the side facing the sound source is crucial. Sound-absorbing materials effectively reduce sound reflection on the barrier surface, preventing reflected waves from bypassing the top of the barrier or reaching the receiving point through other paths, significantly improving noise reduction (especially when there are barriers on both sides of the road). Barriers with good sound absorption performance can reduce noise by an additional 3-6 dB(A) compared to barriers without sound absorption.
5. Frequency characteristics: The sound barrier is effective against mid-to-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 and open terrain works best. The presence of reflective surfaces (such as opposite buildings) or complex terrain will reduce the effectiveness.
7. Atmospheric conditions: Temperature gradient, wind direction and speed, etc., will affect the sound propagation path, and thus affect the actual effect.
III. Differences between fully enclosed and semi-enclosed sound barriers
Typical range:
A well-designed, appropriately high highway noise barrier, located immediately behind a low-rise building, can typically reduce noise by 10–15 dB(A). Under very favorable conditions (such as a high barrier and a close and low sound-receiving point), it may reduce noise by 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 (such as railway noise) from the external environment.
Summarize the key differences
Top structure: Fully enclosed with a top cover, semi-enclosed without a top cover.
Noise reduction mechanisms: Fully enclosed systems rely on physical isolation, while semi-enclosed systems mainly rely on creating sound shadow zones.
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 applications are more widespread and flexible; fully enclosed applications are used in specific sensitive areas where noise reduction requirements are highest and cost is not a concern.
The choice between fully enclosed and semi-enclosed roads requires comprehensive consideration of various factors, including noise reduction targets, project budget, environmental sensitivity, space constraints, ventilation and lighting needs, and landscape impact. In actual engineering projects, sometimes fully enclosed roads are used in certain sensitive sections, while semi-enclosed roads are used in other sections.