I mistakenly believe that the surface is uneven and has a sound absorbing function.
In some early halls, the wall is often decorated with cement bristles, which is considered to have an absorption effect on the sound. There are two main ways of sound absorption, namely, porous sound absorption and resonance sound absorption. Porous sound absorption requires a continuous hole inside the material. Resonant sound absorption requires a cavity, and a structure similar to cement pull has neither internal communication holes. There is no cavity, so there is basically no absorption of sound. This should be taken care of when designing acoustics.
Second, I think that as long as it is a soft bag, it has good sound absorption performance.
In some renovation projects, the commonly used construction is to cover a layer of 2 to 3 mm thick composite soft fabric on the substrate (mostly a large core board or a multi-layer board). This decoration method is simple in construction and good in decorative effect, so it is widely used, but if it is considered that the structure has a good sound absorbing effect because the surface is a soft fabric, it is wrong. Because the sound absorbing performance of the porous sound absorbing material is closely related to the thickness of the material, if the material is too thin, it cannot effectively absorb sound. In general, if the sound absorption effect is to be achieved, the thickness of the sound absorbing material should be at least 10 mm, otherwise it cannot be used as a sound absorbing structure. It is of course also possible to enhance the sound absorption of the structure by providing a cavity behind the porous material. In general, if the sound absorption effect is to be achieved, the thickness of the sound absorbing material should be at least 10 mm, otherwise it cannot be used as a sound absorbing structure. Of course, it is also possible to enhance the sound absorption of the structure by providing a cavity behind the porous material. The method is to have a certain cavity from the wall when installing the raft, the thickness of the cavity should be greater than 30 mm, and the substrate should not be too thick. It is preferable to have a five-ply plate or a nine-ply plate to open a hole or a slit of a certain area on the substrate. If you want to enhance the low-frequency sound absorption, you can determine the perforation rate according to the formula (4-4) of this chapter. If you want to enhance the mid-high frequency sound absorption effect, you need to open a larger hole, the porosity should be greater than 30%, and the aperture is also Should be greater than 20mm. This method enhances the sound absorption of the structure without changing the decoration effect.
Three mistakes that as long as the sound-absorbing material is placed, there is a sound absorption effect.
In some decoration constructions, the porous sound absorbing material is placed behind a plate such as a splint or a gypsum board. In this case, the sound absorbing material does not function to absorb sound. Because the first condition of sound absorption of porous materials is that sound waves can enter the interior of the material, and this configuration causes the sound to be reflected back by the sheet in front of the sound absorbing material, and cannot enter the inside of the material, so it cannot function as sound absorption. . If the front plate is relatively thin, the cavity behind the plate is relatively large and can be used as a thin plate sound absorbing structure. At this time, if some porous sound absorbing material is filled in the cavity, the width of the structure sound absorption band can be increased, but the porous sound absorbing material can only play the role of auxiliary sound absorption, not the main action, and the sound absorption effect thereof. Nor can it be compared to the case where the sound absorbing material is exposed to the sound field.
4. Destruction of the sound permeability of the surface of the porous material or the facing material during construction
As mentioned above, the primary condition for ensuring the sound absorbing properties of porous materials is to ensure good sound transmission properties on the surface of the material. However, in some renovation projects, because the construction personnel do not understand the acoustic requirements, they often take some inappropriate construction measures, which destroy the original sound absorption effect of the materials. The common ones are as follows:
A. Paint or paint on the surface of porous sound absorbing material
The most common is the mineral wool decorative sound absorbing panel used for the ceiling. In some projects, the surface of the mineral wool sound absorbing board is stained during construction. In order to beautify, the surface of the board is painted with a layer of paint or paint. The cavity of the board is sealed, so that the sound wave cannot enter the inside of the sound absorbing material, which seriously affects the sound absorption performance of the material. The correct method is to keep the surface of the board clean as much as possible when installing the mineral wool decorative sound absorbing board, and no longer handle it after installation.
B. Damage to the sound permeability of the facing material due to processes such as brushing
In practical use, the porous sound absorbing material often needs to be installed with a sound-permeable finishing material on the outside of the material. The typical structure is a glass wool board surface covered with a glass wire cloth or a non-woven fabric, and a metal mesh or a perforated plate is installed outside. . Sometimes, the glue is applied to the glass cloth to adhere the glass cloth, the non-woven fabric and the metal mesh or the perforated plate. Sometimes the structure is installed and then the putty is painted on the surface of the metal mesh or the perforated plate, or the spray is applied. coating. These practices will destroy the sound transmission properties of the facing material, so that the sound waves can not touch the sound absorbing material, thus destroying the sound absorbing performance of the structure. The correct method is to use a point sticking method when bonding glass fiber cloth or non-woven fabric. Do not brush the glue on a large area of ​​the cloth, and the metal mesh or perforated board should be painted before painting or coating to ensure the facing material. Has good sound permeability.
Five mistakes that the perforated plate has good low frequency sound absorption performance
The perforated plate combined resonant sound absorbing structure must have two necessary conditions. First, the panel must have a certain perforation rate, and second, the cavity must have a certain thickness after the plate, and both are indispensable. In some projects, the perforated plate is attached to the wall or other materials, and there is no cavity behind the plate. This situation does not achieve the low-frequency resonance sound absorption. In other projects, semi-perforated plates are used so that sound waves cannot enter the cavity through the holes, and the resonance sound absorption is also not achieved. In addition, the perforation rate of the perforated plate for the perforated plate combined sound absorption structure mainly for absorbing low frequency is not too large, generally not more than 8%, and the perforated plate having a large perforation rate is generally used as a sound-permeable decorative material. The effect of low frequency resonance sound absorption is weak.
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