An Electronic Factory Boundary Noise Control Project Case

A certain electronics factory in Shenzhen has arranged multiple sets of exhaust fans, air compressors, central water towers, and other equipment on the roof of the production building. The noise generated during normal equipment operation is excessive, adversely affecting the acoustic environment of the employee dormitories on the north side of the company. The company attaches great importance to the noise issue and has invited Huiyun for on-site inspection to provide a reasonable solution. The site falls under the third-class sound functional area in the "Environmental quality standard for noise" GB3096-2008. The noise value at the dormitory building during the day should be ≤65dB(A), and at night, it should be ≤55dB(A). The owner has raised the standard requirement, requesting us to reduce it to below 54dB(A).

 

 

 

Environment Overview

Through on-site inspections, we have gained a preliminary understanding of the noise sources from equipment throughout the entire factory. Our technical personnel have set up 20 noise survey points in 14 different areas and collected noise data from sensitive points. By collecting noise data, conducting spectrum analysis, noise superposition and attenuation calculations, and combining it with the acoustic simulation software Cadna-A, we simulated the on-site acoustic environment. This provides a theoretical basis for the subsequent noise assessment.

 

 

Noise value test results

Through multiple measurements on the night of May 20 and during the day of May 21 and 30, the following noise values were obtained:

 

 

Based on the above measurement data and on-site inspection, the acoustic environment of the dormitory is not only affected by the noise from the production building’s roof equipment, but also influenced by the road vehicles, canteens and dormitory buildings. However, the measurement data above excludes the impact of vehicle noise, only considering environmental sounds (e.g., wind blowing through leaves, insect calls, etc.). After communication with the owner, the impact of the canteens and the dormitory building’s roof equipment is not taken into account in this case. The focus of this project is solely on addressing the roof equipment of the production building. From the measurement data, it can be observed that the noise value at sensitive points exceed the nighttime standards by 4-5 dB(A), with an environmental background noise of 54.0 dB(A). 

 

Noise source intensity and noise transmission analysis

Based on the on-site survey, it was found that the noise sources in the factory area are primarily divided into the following areas:

①Air Compressor Room: The vent was later moved outside the room, affecting the sensitive points.

②Waste discharge unit: The original factory building has simple sandwich panels, and there are many openings in the panels, resulting in inadequate sound reduction index, with noise directly transmitted to sensitive points.

③Central Water Tower: The original factory building is constructed with a single-layer color steel plate, and the sound reduction index does not meet the requirements.

④Air conditioning room: The original factory building has poor sealing. UV Photolysis Fan: The fan's outlet noise is relatively high.

 

Analysis of Sensitive Points Noise

The measured day and night noise values at sensitive points on-site are as follows:

 

 

Based on the on-site inspection and measurement data, it can be observed that:

①The noise values at sensitive points exceed the requirements of the national Class III standards.

②The main affected floors are the 7th, 8th, and 9th floors. From the daytime measurement data on the 30th, the environmental background noise for this project is around 54.0 dB(A).

 

Noise Spectrum specificity analysis

 

This spectrum analysis takes the example of the waste discharge unit, which has a major impact on sensitive points. Based on on-site measurement data, the following spectrum characteristic curve is derived:

 

The noise spectrum curve shows that the frequency corresponding to the noise peak is 500Hz, which falls into the category of mid-low frequency noise. Low-frequency noise differs from high-frequency noise. High-frequency noise rapidly attenuates with increasing distance or encountering obstacles. For instance, a point source of high-frequency noise can decrease by 6 decibels every 10 meters. In contrast, low-frequency noise attenuates much more slowly. Due to longer sound waves, it easily traverses obstacles, traveling long distances, and penetrating walls directly into the ears. Vibration, low-frequency noise, and general noise share a common characteristic as forms of vibrating waves and ways of energy propagation. When outdoors or with doors and windows open, low-frequency noise is often masked by other mid-to-high-frequency noise components, making it less noticeable. However, when doors and windows are closed, mid-to-high-frequency noise is blocked by soundproofing, making low-frequency noise more pronounced. Therefore, in quiet or late-night settings, the interference of low-frequency noise is more easily perceived. Low-frequency noise can create a sense of oppression in individuals, significantly impacting sleep and mental well-being. It may lead to conditions such as neurasthenia and depression, with older individuals being more susceptible to its effects.

 

Treatment Scheme

In response to the identified noise sources, Huiyun has devised a comprehensive solution involving sound insulation, noise suppression, and sound absorption measures. Through the combination of these measures, on-site equipment noise has been effectively addressed, providing adequate protection for the acoustic environment at sensitive points. 

 

Design drawings for the treatment of the waste discharge unit area

Design drawings for the treatment of the central water tower area 

Acoustic Environmental Simulation Software

Before Treatment Acoustic Environment Condition >>>

The software simulates the acoustic environment condition at the 9th floor, which is the height of the sensitive point. The isochromatic lines map below illustrates the distribution of the acoustic environment condition on the 9th floor.

 

Simulation Results Before Treatment (58 dB(A) at the sensitive point)

Software Model Diagram Before Treatment

After Treatment Acoustic Environment Simulation >>>

 

Internal Single Point Treatment Simulation Diagram (48 dB(A) at the sensitive point)

Simulation Model Diagram After Treatment

 

Construction Photo Showcase

Steel Structure Installation >>>

 

 

 

Acoustic Hood Installation >>>

 

 

 

Muffler Installation >>>

 

 

 

Construction Completion Photos >>>

 

 

 

 

 

Post-treatment Effect

After the implementation of the above measures, the noise values measured at sensitive points all meet the standards for Class 3 areas specified in the "Environmental quality standard for noise"( GB3096-2008). During on-site testing at night, the measured noise values at sensitive points ranged from 53.7 to 54.0 dB(A), meeting the goals of this design and achieving significant improvement in the acoustic environment at sensitive points. The owner has given full affirmation to this noise control project!