The propagation of noise generally occurs in three stages: the noise source, the transmission path, and the receiver. The transmission path includes the progression of sound waves in forms such as reflection and diffraction. The principle of noise control is to dampen, isolate vibrations, absorb sound, and prevent the noise from reaching the eardrum before it does.SoundproofingSeven measures include mufflers, personal protection, and building layouts, all aimed at reducing or dampening the vibration of the sound source, absorbing transmitted sound energy, or setting up barriers to reflect the sound completely or partially, thereby lessening the impact of noise on the eardrum, achieving the goal of noise control. 
 　 
Based on the three stages of noise propagation, three different methods can be employed to control noise. 
（1) Reduce noise at the source 
This is a fundamental aspect, including measures such as developing and adopting low-noise equipment and processing technologies. The main causes of noise are the vibrations from airflow, solid impacts, and friction, as well as the vibrations of the iron core caused by magnetostriction. Aerodynamic noise from fans, jet aircraft, and car exhausts can be controlled by using smooth airflow channels and reducing the speed of the airflow. Mechanical noise from machine tools, looms, and riveting machines can be controlled by using lubrication or damping materials to reduce friction or impacts. Electromagnetic noise from motors and transformers is often reduced using silencers. Other measures such as replacing high-noise hammering with silent hydraulic systems, using welding instead of riveting, improving the design of fan blades, and enhancing the processing accuracy of gears and other transmission components, as well as balancing operating parts to reduce vibrations caused by eccentricity, can all significantly lower noise at the source. 
　 
（2) Control noise in the transmission path 
This method involves acoustic treatments such as sound absorption, noise insulation, vibration isolation, and damping to reduce noise levels. Since noise is transmitted through the air or through the equipment or the building itself, this approach can effectively control it. The use of sound-absorbing materials like glass wool, felt, foam plastics, and acoustic bricks, along with resonant and micro-perforated plate sound-absorption structures, can reduce indoor noise reflections and lower noise by 10 to 15 decibels. The sound-insulating materials used in sound-insulated rooms and enclosures are heavy, so they typically include bricks, reinforced concrete, steel plates, and thick wood panels. Additionally, structural sealing is essential, ensuring no holes. A sealed enclosure can generally reduce medium to high noise levels by 10-35 decibels, with a double-layer structure reducing weight by about 70% compared to a single-layer structure, making it more economical. However, attention must be given to prevent resonance in the middle air layer. Filling with soft sound-absorbing materials can both absorb sound and reduce the vibration of the layers. When using metal plates for sound-insulating enclosures, the interior surface should be treated for sound absorption, and the exterior should be coated with damping materials. This is combined with external components (supporting devices) and adhesive dampers (energy consumption devices). Common vibration-isolation materials include shear rubber, metal springs, cork, slag wool, glass fiber, and air cushions, with the first two being widely used domestically and the latter being the direction of development. Generally, vibration-isolation pads can reduce low-frequency noise by about 10 decibels. Damping materials are those with high internal frictional losses, such as asphalt, soft rubber, and other high polymer coatings. They can dissipate the vibration energy of metal plates into heat, thereby suppressing bending vibrations and preventing noise radiation. Fully understanding the sound generation mechanism can lead to economic and effective noise reduction. 
（3) Block noise at the receiving point 
In the event that the aforementioned control methods fail, personal protective measures such as earplugs, earmuffs, noise-blocking cotton, and protective shields should be employed. These protective devices must be airtight to effectively block sound, but their design may allow some low-frequency or low-intensity sounds to pass through, ensuring noise reduction without hindering conversation. 
　 
However, the most effective and economic method to control urban noise is not initially technological measures, but rather public awareness campaigns. These campaigns should educate the public about the sources, hazards, and control measures of noise, and widely mobilize them to control noise. Second is the enhancement of administrative management, with a crucial focus on the national establishment of noise control standards, regulations, and the necessary laws and regulations for their implementation. Regional planning should rationally locate residential areas away from noise sources to minimize the impact of traffic and industrial noise. Other measures, such as restricting the use of loudspeakers, converting trolleybuses to underground or wireless operation, and strengthening management and taking appropriate measures for traffic vehicles, construction machinery, living noise, and factory noise, can also achieve significant effects.。