1. Eliminate sound.
Absorption noise reduction method: Absorption car muffler reduces energy by friction of exhaust gas on sound-absorbing materials such as glass fiber, steel fiber, and asbestos.
Reflection noise reduction method: The reflection muffler has several series connected harmonic chambers, connected by porous reflection tubes of different lengths. The exhaust gas undergoes multiple reflections, collisions, expansion, and cooling to reduce its pressure, vibration, and energy.
2. Types of mufflers and their working principles.
Muffler: This type of muffler contains porous tubes, sound-absorbing fibers, etc. The exhaust gas vibrates through the muffler, and due to friction and bonding, vibration and heat energy are generated. The noise changes during this process, so it is also called sound-absorbing. The specific shape of resistive mufflers varies, and the direction of airflow also varies.
Resistive silencers have the characteristic of small volume, so most original car drums prefer to use resistive silencers. If you want to fully utilize their noise reduction function, the installation position is generally closer to the engine direction. Many experimental results have shown that resistive mufflers have a better suppression effect on engine mid to high frequency noise than mid frequency and mid frequency mufflers. Similarly, the performance of anti ventilation is exactly opposite to that of resistance.
Resistance muffler: This type of muffler structure does not have sound-absorbing cotton and is mainly composed of partitions and expansion chambers. A regular muffler has three expansion chambers of different sizes. The exhaust is used to reflect and interfere with each other (friction) in these chambers to achieve noise reduction effect. Larger chambers are more conducive to noise processing, but their size is also limited by the shape of the chassis. SUVs such as Audi Q7 and BMW X5 have this advantage.
In addition, due to different usage methods, the volume of the resistant muffler is larger than its resistance, so it is often installed at the rear. The obvious suppression effect on medium and low frequency noise has won many praises from the original factory.
Change the tube and chamber composition of the interface to form a "sound filter" to reduce noise;
Impedance type muffler: The structure of the composite muffler combines the first two types of mufflers together, that is, it has both a sound absorption chamber and a sound amplification chamber. This indicates that at the engine speed, the two types of mufflers have their own strengths and weaknesses. The composite type can balance the two characteristics well and has a larger volume.
Most car modification rings use resistance type and composite type mufflers, which are related to exhaust back pressure. On the basis of the composite tail drum, China further divides it into S drum, G drum, H drum, etc. in the shape of porous tubes.
Micro perforated plate muffler: This muffler is a type of muffler lined with a micro perforated structure. It has a wide range of ability to eliminate airflow noise and has good heat resistance, oil resistance, and corrosion resistance. Even if there is a large amount of moisture in the airflow, it does not affect the work. Because the resistance loss of a muffler is smaller than that of a typical resistive muffler due to its small aperture and smooth surface.
Microporous plate silencers are usually made of pure metal sheets, and holes are drilled on the sheets with a drill bit with a diameter less than 1mm, with a perforation rate of 1% to 3%. By selecting cavity depths with different perforation rates and plate thicknesses, the spectral characteristics can be controlled to achieve good noise reduction within the desired frequency range.
Muffler: This muffler structure is a straight pipe with one end closed and many small holes drilled on the pipe wall. Its principle is designed based on the spectral characteristics of jet noise. While keeping the total area of the nozzle unchanged, many small nozzles are used instead. When the airflow passes through the small holes, the spectrum of jet noise will shift towards high or ultra-high frequencies, significantly reducing the audible sound groups in the spectrum and reducing interference and harm to the human body.
The perforated muffler has low to medium frequency broadband noise reduction performance. A small aperture can improve the sound absorption coefficient, a low porosity can increase the frequency band width, and the depth of the orifice plate can change the position of the resonance absorption peak. It has the advantages of tight design, frequency band absorption, low impedance loss, high temperature resistance, and long service life. The exhaust system of boilers, compressors, and other high-pressure equipment generally adopts venting.
Muffler: This type of muffler is a set of instrument devices mainly composed of microphones, amplifiers, phase shifters, amplifiers, speakers, etc. It produces a sound wave with the same sound pressure magnitude but opposite phase to cancel out the sound wave in the original sound field, thereby achieving noise reduction.
Active silencers are widely used in industrial plants and mines such as power generation, chemical, metallurgical, and textile industries, and are used in various types of boilers and steam turbines; Fan; Silencing of safety doors and other equipment.
