At present, the control of low-frequency noise is still a technical problem. To control and reduce low-frequency noise, the soundproof window of Shanghai butterfly valve electric butterfly valve manufacturer believes that the low-frequency noise should be solved according to its own point and transmission path: control the low-frequency noise transmitted by air:
Air borne sound transmission means that low-frequency noise is directly transmitted to the residential area through the air. The typical low-frequency noise is traffic noise. This noise mainly includes the sound generated by the automobile engine, the sound generated by the friction between the tire and the road, and the sound generated by the motor vehicle driving to overcome air resistance. The pollution of traffic noise to buildings on both sides of the road depends on the type of motor vehicles running on the road; In general, the pollution of small passenger cars is relatively small, and it is not difficult to control. Large trucks and large tourist buses are relatively polluted. The noise frequency generated by the engine is mainly concentrated in the low frequency and below 200Hz, and the noise can reach more than 90dB. The faster the traffic noise is related to the speed of passing vehicles, the higher the noise is, The degree of traffic noise pollution is also directly related to the load of vehicles. The greater the load, the greater the noise. Traffic noise has a greater impact on the pollution of buildings along the line and the distance between buildings and the road. The closer the distance from the road, the greater the impact. Noise has different effects on different floors. The general rule is that low floors are more seriously polluted by noise, and it is more difficult to control.
Air borne low-frequency noise control:
Plan the distance between urban roads and buildings, and set up sound barriers for main roads, expressways, expressways, and low-frequency noise sensitive areas along the line;
The use of new urban pavement materials can reduce the noise generated by tires when driving on the road;
Minimize large trucks and trains passing through urban residential areas, especially at night;
Use environmentally friendly and low noise pollution buses, and eliminate buses with high energy consumption and noise pollution;
Install sound proof windows for sound insulation;
2. Control low-frequency noise of standing wave
Standing wave refers to the standing wave formed by multiple reflections of low-frequency noise in the propagation process. The amplitude and intensity of low-frequency noise in the wave belly are very strong, which is harmful to human health. The urban noise, big, and extensive are road traffic noise. The nature of traffic noise is low frequency, point, and the peak value of sound pressure level is 50 hz at the center frequency point. The wavelength of sound at 40 hz, 50 hz, and 63.5 hz is 4.3 meters, 3.4 meters, and 2.7 meters, which is very close to the size of rooms on both sides of the road. When traffic noise reaches the rooms on both sides through air transmission, The above frequency noise will produce resonance in the room, forming standing waves. Shanghai Dongfeng suggested that there are two main methods to control standing wave hazards:
a. Change the layout of the room furniture. By changing the position of the furniture, especially the position of the bed and desk, we try to avoid the position of the standing wave peak generated by the 40 hz central frequency of the traffic noise, so that we can work and sleep normally.
b. Arrange space around the room to absorb sound. For example, the wall at the standing wave position is made of sound absorbing materials or soft packaging; The above are some suggestions and methods of Shanghai Dongfeng electric butterfly valve manufacturer for low-frequency noise control. The low-frequency noise caused by air sound transmission is easy to be isolated, while the structural sound transmission is relatively difficult. The ones that are difficult to harm and big are standing waves. In addition, the standing wave generation is generally sound insulation measures for doors and windows, which cannot be avoided. We will continue to develop new products, Energy reduces the harm of noise. Low frequency noise of control structure transmission:
Structural sound transmission means that transformers, water pumps and central air conditioning hosts installed in the building transmit low-frequency vibration sound waves to each household through the basic structural girders and load-bearing beams of the residential building. In view of the performance of low-frequency noise caused by structural sound transmission, it is considered that the valve noise should be reduced at the source of noise.
A. The noise of the transformer comes from the transformer body and the cooling system. Therefore, the manufacturer of Shanghai butterfly valve electric butterfly valve believes that the noise reduction of the transformer needs to start from two aspects. On the one hand, the noise of the transformer body can be controlled by reducing the vibration of the iron core and reducing the noise emission capacity; Noise can also be attenuated in the transmission path through vibration reduction, sound insulation, sound absorption and other measures. On the other hand, control the noise of the cooling system to make it close to or lower than the noise level of the body, which can also effectively reduce the noise of the transformer.
B When the pump is running, the low-frequency vibration generated by the motor rotation spreads along the building structure, which has a great impact on the upstairs/downstairs rooms. The noise in the room sometimes reaches more than 55dB, and the humming low-frequency noise makes people feel uncomfortable. Vibration transmission, up to 30 floors high. Therefore, it is necessary to design valve sound insulation technology for pumps and pipelines against low-frequency vibration, and adopt valve sound insulation treatment. From our practice, it is necessary to design multi-stage vibration isolation technology to isolate vibration transmission at different frequencies for such low-frequency vibration. So as to achieve the goal of valve noise reduction.
C. The sound transmission of the air conditioning host is partly air borne, which enters the room through doors and windows, and partly through the vibration of the wall. The low-frequency noise transmitted by the external unit of the air conditioner through the air can be separated by soundproof windows; For those that transmit sound through structures, the foundation of air conditioning equipment shall be equipped with vibration damping devices according to the specifications. The structural noise generated by the excitation force of the equipment shell shall be coated with macromolecule damping materials with large internal friction. The manufacturer of Shanghai Dongfeng electric butterfly valve suggested that the vibration isolation and damping technology can effectively reduce the structural noise caused by the excitation force. The solid vibration has low transmission frequency, long transmission, slow attenuation and wide influence range.