General rules and acoustic knowledge of building soundproofing members
1. The law of mass There is a general rule for the sound insulation of partition walls, that is, the heavier the material (the density of the surface, or the greater the mass per unit area), the better the sound insulation effect. For a single-layer dense-density wall, the surface density increases by a factor of 6 dB, and this law is the law of mass. For double-layer gypsum board walls, the mass law plays an important role, that is, increasing the number of layers or thickness of the board can improve the sound insulation. Since the form of audible vibration of the keel double-wall system is very complicated, the embodiment of the mass law is more complicated than a simple single-wall. The sound insulation effect of the single-layer gypsum board is very poor. For example, the standard weighted sound insulation of the gypsum board of 12 mm thick and the surface density of about 10 kg/m2 is Rw=29 dB. Even if four layers of such gypsum board are stacked and the sound insulation amount is theoretically Rw can only reach 41dB. Lightweight homogeneous walls, such as gypsum blocks, aerated concrete slabs, expanded perlite slabs, lightweight perforated plates, etc., the surface density is mostly 60-100kg/m2, which is limited by the mass law, and the sound insulation quantity Rw=35- 40dB. For single-layer heavy wall, the areal density is more than 250kg/m2, such as 120 brick wall, 90 thick hollow concrete block, 100 thick concrete wall board, etc., the sound insulation Rw can reach about 45dB, and the surface density exceeds 500kg/m2. The sound insulation of 200 thick concrete walls can reach 50-55dB. 2. Resonance frequency Any partition wall has an inherent resonance frequency. When the frequency of the sound wave and the resonance frequency of the wall are the same, the whole body will resonate, and the sound insulation of this frequency will be greatly reduced. Generally, the thicker the wall, the lower the resonance frequency. When the resonance frequency is lower than the minimum reference frequency of 100 Hz for sound insulation evaluation, since the hearing characteristics of the human ear are not sensitive to the low frequency, the influence on the sound insulation amount Rw is greatly reduced. There are different resonance frequencies for two different areal density gypsum boards of 12 mm and 15 mm thickness. The surface density of 12mm gypsum board is 10kg/m2, and the surface density of 15mm gypsum board is about 12kg/m2. The resonance frequency of 15mm thick gypsum board wall is basically lower than the minimum considered frequency range of 100Hz, so the resonance frequency is 15mm board. The wall member of the constructed wall has less influence on the sound insulation performance. However, for the 12mm board, the sound insulation performance near 100Hz has a great influence, causing the sound insulation at low frequency 100Hz, 125Hz, 200Hz to drop more than the 15mm board, mainly because of the resonance frequency. 3. Matching effect After the acoustic wave contacts the wall panel, in addition to the forced vibration in the vertical direction, the wall panel has forced bending vibration along the direction of the panel surface. At a certain frequency, the forced bending vibration will coincide with the inherent free bending vibration of the plate. At this time, the plate follows the incident acoustic bending very compliantly, causing the sound energy to be transmitted to the other side in a large amount to form a soundproof amount. The trough, this phenomenon is called the anastomosis effect, and this frequency is called the coincidence frequency fc. Both theory and experiment show that the light, thin and soft wall fc is high and the anastomosis effect is weak; the thick, heavy and rigid wall fc is low and the anastomosis effect is strong. The fc of the 12mm and 15mm gypsum board is about 3.15KHz and 2KHz, respectively. The sound insulation of the 12mm board is reduced at 3.15KHz, and the sound insulation of the 15mm board is more serious at 2KHz. Even the downward trend is stronger than the mass law, resulting in a much lower sound insulation than the 12mm board at this frequency position. . The double-sided identical plate overlap frequency fc is basically equivalent to the single-layer plate. Due to the vibration superposition of the double layer, the anastomosis effect is more severe, and the anastomotic valley becomes deeper. If sheets of different thicknesses are used for lamination, the anastomotic valleys will be staggered from each other, and each of the anastomotic valleys is shallow, which is advantageous for sound insulation. The strong anastomosis effect of the double-layer board is very obvious, and the partition wall of the double-layer 15mm board structure is lower than the partition wall of the double-layer 12mm board. The partition wall with a layer of 12mm and a layer of 15mm is lower than the double-layer 15mm partition, but the sound insulation will increase, which is the result of the weakening effect. The factors of the anastomosis effect are more complicated, which are related not only to the areal density of the material, but also to the elastic modulus, thickness and Poisson's ratio of the material. Foaming in the production of gypsum board affects these factors, including the most direct areal density. From a large number of experiments, we have found that reducing the areal density within a certain range, the frequency of the anastomosis will become higher, and the anastomotic effect will be weakened, which is advantageous for sound insulation. There are light-weight partition walls with large surface density and thicker, such as aerated concrete slabs and gypsum blocks. The frequency of the anastomosis often appears in the range of 250-2000 Hz. The heavier and thicker the light board, the more soundproof A deep “matching valley†appears in the low frequency range of the curve, which severely limits the sound insulation of the wallboard. Even if it is made into a double wall with an air layer in the middle, the sound insulation is not high due to the superposition of the matching effect. For example, a double-layer 90-aerated concrete slab, hollow 50mm, the sound insulation can only reach about 48dB, and the same weight The sound insulation of the double-row keel six-layer 12mm gypsum board wall can reach 60dB, which is mainly because the anastomosis frequency of the 12 gypsum board is high, and the anastomosis effect is not strong with the 90-aerated concrete slab. 4. Sound bridge When the plate is directly fixed on the keel, the vibration of the sound side plate will pass through the keel to the other side plate. This phenomenon of transmitting sound energy like a bridge is called a sound bridge. The more the sound bridge, the larger the contact area and the stronger the rigid connection, the more serious the sound bridge phenomenon and the worse the sound insulation effect. An elastic pad is added between the plate and the keel, such as an elastic metal strip or an elastic material pad, which can improve the sound insulation of the gypsum board wall by a certain amount, and can be increased by up to 3 dB. In addition, the light steel keel itself has a relatively small stiffness, and the acoustic bridge effect on the plates on both sides is better than the wooden keel and gypsum keel of the rectangular cross section. The light steel keel gypsum board partition wall has better sound insulation effect than the wooden keel and gypsum keel partition wall of the same structure. it is good. For the light steel keel gypsum board wall, in order to reduce the sound bridge and obtain a higher sound insulation, the keel structure is sometimes made into a staggered structure and a double layer structure. The staggered structure is that the vertical keels are staggered and separated, the two sides of the slab are not fixed on one keel at the same time, and the heaven and earth keels share one set; the double-layer structure is that the heaven and earth keel and the vertical keel are respectively made of two layers, and there is no connection in the middle, and the plates are fixed in their respective On the keel. In theory, the staggered keel wall insulation is better than the ordinary keel partition, which can increase 1-3dB; the double keel partition is better than the staggered keel partition, which can improve 7-8dB compared with the ordinary keel partition. The increase in sound insulation is due to the weakening of the sound bridge. 5. Slits and holes If there are gaps and holes in the partition wall, the sound insulation of the partition wall will be greatly reduced. If the wall of the partition wall itself has a sound insulation of 50 dB and the wall has one ten thousandth of a gap and a hole, the overall sound insulation will drop to 40 dB. In order to prevent gaps between the gypsum board wall and the original structure, plastic elastic strips are usually placed when the keel is installed around the wall. In addition, when there are two layers of gypsum board on each side, it should be installed by mistake, the inner layer can be unstitched, and only the outer layer is jointed, which has little effect on the sound insulation of the partition wall. However, each layer of the board must be jointed, otherwise the sound insulation will be reduced by 12-17dB.
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