Which acoustic technologies have yielded significant results in urban noise control?

In an evening in a residential area of ​​Qingyang District, Chengdu, square dancers dance to music, while the apartment buildings just steps away remain quiet. The noise from square dancing, shop hawking, and equipment malfunctions that once plagued residents seem to be isolated by an invisible barrier. This change is thanks to the increasingly sophisticated application of acoustic technologies in noise control.

Across the country, from square dancing noise to traffic rumble, from construction disturbances to equipment malfunctions, cities are using various acoustic technologies to restore tranquility to their residents.

I. Intelligent Monitoring: Equipping Noise Control with "Electronic Ears"

Traditional noise control relies on manual inspections and resident complaints, which are often slow and inefficient. Now, intelligent monitoring technology is shifting urban noise control from a "passive response" to a "proactive management" approach.

In Anshan City, Liaoning Province, 15 automatic noise monitoring stations in functional areas operate 24 hours a day, collecting parameters such as equivalent sound level and maximum sound level in real time, and automatically identifying various noise sources, including construction, social life, industry, and traffic.

The "Quiet Community" in Chengdu's Qingyang District has introduced a more sophisticated intelligent sensing and monitoring system. This system uses front-end detection equipment as its "eyes and ears," and a back-end "acoustic cloud" platform as its "brain," forming a closed loop from data collection to intelligent management. The acoustic cloud platform, through real-time voiceprint recognition technology, can accurately distinguish different noise types, such as square dance music, vehicle horns, and shop hawking. Once excessive volume is detected, the system automatically generates an alarm and pushes it to management personnel, achieving proactive management.

II. Soundproof Windows: The "Last Line of Defense" for Home Peace

For existing densely populated urban areas, especially residences facing fixed noise sources such as main traffic arteries and commercial areas, soundproof windows, with their immediate effect, become the "final protection" for safeguarding home tranquility.

Social noise is random and dispersed, making it difficult to completely eradicate through public governance. Installing high-performance soundproof windows in residential buildings, schools, and hospitals facing streets is equivalent to putting "noise-proof armor" on every private space.

High-quality soundproof windows use laminated glass, double-glazed glass, or composite structures, utilizing different media to block sound wave propagation. Through a sealed window frame design, they can effectively block 20-35 decibels of outdoor noise. In several "Quiet Home" renovation projects, after replacing windows with soundproof ones, the indoor sound environment dropped from a noisy 60-70 decibels to a quiet level below 35 decibels, achieving library-level quietness.

Especially for infants, the elderly, and those working from home, soundproof windows greatly protect their quality of life and health. They are the most direct and accessible "hard barrier" in the noise control system.

III. Directional Sound Technology: Targeting Sound Effectively

Noise from square dancing used to be a major urban management problem, but the application of directional sound technology has solved this problem.

In a Chengdu residential community, Ms. Wang, a member of a dance troupe, said, "Before, I was always careful, constantly watching the decibel screen, afraid of disturbing the neighbors while dancing. Now, with this 'magical speaker,' the dance area is clearly audible, and the surrounding area is quiet. I no longer have to live in fear."

This technology originates from the application of ultrasonic carrier wave and beamforming technology, enabling sound to propagate directionally like a beam of light, creating a "sound curtain" effect. Yu Zihao, General Manager of Didong Technology, explained that this technology can achieve a sound pressure level difference of over 30 decibels between the front and rear, and the sound field coverage is flexibly adjustable.

Similar technology has also been successful in Wuhan and Meishan. After the Meishan Municipal Housing and Construction Bureau installed directional speakers in Sumu Park, the melodies in the park were clear, while nearby residents' homes regained their tranquility.

IV. Sound Barrier Upgrade: An "Invisible Wall" Blocking Traffic Noise

Traffic noise is one of the main sources of urban noise pollution. To address this issue, sound barrier technology is constantly being upgraded and iterated.

Studies have shown that for urban elevated roads with high traffic volume, when noise-sensitive targets are close and mostly high-rise buildings, fully enclosed sound barriers are more effective than conventional folded-plate sound barriers.

A study of elevated roads in Wenzhou City shows that fully enclosed sound barriers reduce noise by 15.1–17.2 dB during the day and 10.0–12.3 dB at night at a distance of 21 meters. When sensitive points are within 25 meters of the elevated road, the daytime noise reduction difference between fully enclosed and semi-enclosed sound barriers is 6.4–8.6 dB.

However, the study also points out that not all situations require expensive fully enclosed sound barriers. The most suitable solution should be selected based on the actual situation, optimizing from an economic perspective.

V. Source Reduction: Addressing Noise Problems at the Generation Mechanism

In addition to blocking noise transmission, reducing noise generation at its source is also an effective control strategy.

In the "Quiet Community" of Qingyang District, Chengdu, a special task force installed shock-absorbing rubber mats on the entrance and exit lanes of the underground parking garage, eliminating the metallic clanging noise from manhole covers when vehicles passed by. Simultaneously, they comprehensively upgraded all aging fitness equipment, reinforcing and lubricating connecting parts to eliminate metallic collision and friction noises.

In the industrial sector, SMAC moving-coil actuators reduce noise levels by more than 50% compared to traditional pneumatic actuators. Pneumatic actuators have a noise range of 100–120 decibels, while SMAC moving-coil actuators only produce 40–60 decibels, equivalent to a quiet library or office environment.

VI. Rapid Response: Establishing a Long-Term Mechanism for Noise Control

Beyond technical means, establishing a rapid response and long-term management mechanism is equally crucial for noise control.

The "Quiet Community" in Qingyang District has established a "1-5-60" rapid response mechanism: 1 minute for receiving an alarm, 5 minutes for on-site arrival, and 60 minutes for resolving the issue. Meanwhile, an "8+7" working mechanism and management system, along with a "345" publicity mechanism, were established. Noise control publicity was conducted in buildings, units, and homes, combined with four-level inspections and five-item checks, improving control efficiency by 70%.

Shenzhen launched a "remote stop system" for construction noise. This system uses monitoring equipment, the Internet of Things, and sensors to collect noise data in real time. When noise reaches warning or exceeds the standard, the system automatically issues a remote warning via loudspeaker. This approach solves the problem of insufficient enforcement personnel and greatly increases the possibility of on-site enforcement, to some extent ending the "cat-and-mouse game" of noise control.

From Chengdu's "quiet communities" to Wuhan's "quiet dance halls," from Anshan's "electronic ears" to thousands of households' "soundproof windows," the application of these innovative technologies has made urban noise control more precise and efficient.

A complete noise control system requires not only public means of source control and transmission blocking, but also the protection of personal spaces for end-point protection. Noise control is not only related to the level of urban management, but also directly affects the quality of life of every citizen.