AU2014100430A4 - The improved acoustically resistant composite board - Google Patents

Abstract

ON This invention relates to a composite board with improved acoustical resistance for use in construction of the partition walls, ceilings or flours in buildings and to soundproof aircraft engines or any place where noise reduction is required. A multi layer composite board comprises layers (11) of material with specified in advance surface density and thickness whereby the frequency band is extended due to increased critical frequency of the board (10). Gaskets or suitable adhesive materials between layers (12) provide a layer by layer propagation of sound waves. 25 25 26 25 Figure 2

Description

1 THE IMPROVED ACOUSTICALLY RESISTANT COMPOSITE BOARD TECHNICAL FIELD [0001] The invention relates to all types of boards used as elements in construction of the partition walls, ceilings or flours in buildings and to soundproof aircraft engines or any place where noise reduction is required. BACKGROUND [0002] A very important problem of acoustic performance is an attainment of ac ceptable airborne sound transmission through constructive elements of different ob jects. [0003] The invention is described in particular application for the building industry though it can be widely used in many fields where noise reduction is required. Build ing elements especially walls, ceilings, windows and doors have to satisfy the sound insulation requirements. Walls also make significant contribution to reduction of noise proliferation in residential and industrial buildings and areas. Constructions of wall lining boards and method of their production have significant impact on sound trans mission loss. [0004] State standards of many countries establish sound insulation ratings of walls. For example, to comply with Building Code of Australia (BCA) walls must have an Rw + Ctr (airborne) not less than 50 if they separate sole-occupancy units. Rw is a weighted sound reduction index and Ctr is a spectrum adaptation term. [0005] The most widely used construction of Partition Wall Systems is Single Stud Wall Construction, based on steel stud with insulation filling and linings of plaster boards. However this method of construction cannot comply with the BCA Rating of Sound Insulation, because of the acoustic characteristics of the mainstream com mercially available lining boards that cannot achieve required sound transmission loss in the partition walls.

2 [0006] To comply with BCA, builders usually use Staggered Stud Walls, Double Stud Walls or apply Resilient Mounts and Furring Channels. These methods significantly increase cost of construction as well as increase thickness of walls thus reducing in ternal space of the buildings. [0007] Acoustica's QuietWave@ wall system comprises 64 mm staggered studs in a 92 mm track with 50 mm thick insulation, two 13 mm thick plasterboard on both stud sides and two 1.2 mm thick QuietWave@ visco-elastic membrane between each pair of plasterboards and achieves compliance with BCA due to staggered studs and vis cose-elastic membranes. [0008] Patent #1998098256 "Acoustic wall" describes construction of wall including a supporting panel, a cavity, and at least one outer surface. The wall contains a rein forced masonry panel having a substantially unitary structure and a cavity defined by the space between the supporting panel and an outer surface. The cavity is wide enough to include an insulation material to increase a sound transmission loss. The outer surface defining the cavity is a single layer of plasterboard. [0009] Patent application EP 1225126 A2 "Acoustic board with an improved compo site structure" describes an acoustic board with improved composite structure, suita ble for reducing sound transmission, in which a upper layer that consists out of fabric, with high sensitivity to sound velocity, and the supporting sheet with a preset porosi ty is combined with one or more intermediate honeycomb layers separated by a po rous septum with a given resistance, and closed by a lower layer for the final cover ing of the structure. [0010] The invention "Acoustical wall panels" US6698543 B2 relates to very struc turally stable acoustical panels that may be of significant size and can be applied di rectly to the wall, or describes actually form the wall panel for a divider, to function dually as a divider, but more importantly, to dampen sound, and lessen the noise re versal of the ambient area. [0011] United States Patent US 3621934 describes a sound-absorbing wall covering for regulating sound-absorption in a room is made in long sheets or rolls of a flexible 3 laminate consisting of a flexible decorative skin such as vinyl adhered to a soft, po rous backing material, preferably a foam polymeric material. Certain areas of the skin contain many very small perforations while the adjoining areas of the skin are imper forate. After installation, a room may be fine-tuned for sound by closing some of the holes in the perforated area. [0012] The invention 2009238349 describes a composite board comprising: "A first and seventh layer of a first thermoplastic material; a second and sixth layer of metal; a third and fifth layer of a second thermoplastic material; and a fourth layer made from a combination of thermoplastic material and a reinforcing filling agent, the fourth layer including at least one hollow void". [0013] Technical solutions of increasing the sound transmission loss (STL) via boards or walls described above achieved by a variety of designs. In order to in crease the reduction of sound transmission, wall constructions include a sound absorbing wall covering or board having an improved composite structure or a sup porting panel and a cavity or elastic membrane between each pair of plasterboards. Sometimes just many layers of different materials are used. [0014] The behavior of board or partition wall under impact of sound waves can be described by three regions of frequency (Ben H. Sharp "Prediction Methods for the Sound Transmission Loss of Building Structures"): (i) the stiffness-controlled region, including the frequencies where resonance occurs; (ii) the mass-controlled region described Mass Low; and (iii) the wave-coincidence controlled region. [0015] In all inventions shown above the dependency of transmission loss of different frequency is determined by chosen construction of boards and walls where each of three frequency regions is defined and fixed. In this case the minimum transmission loss takes place in both ranges the resonance frequency and the coincidence critical frequency. [0016] The objective of this invention is the creation of boards and walls with in creased transmission sound loss compared to the already known boards by expend- 4 ing of the mass-controlled region where transmission loss is the most effective. In this invention the critical frequency can be shifted to high frequencies up to limited test frequency where hearing sound is significantly reduced. [0017] The present invention will ensure that the most simple Single Stud Wall Con structions could comply with the requirements of BCA and still remain at low cost with simplified design and decreased thickness of the walls. In other words, using these innovative boards will allow reaching a predetermined value of transmission sound loss, and at the same time to reduce the overall surface density of the boards, and overall weight and thickness of the wall. SUMMARY OF INVENTION TECHNICAL PROBLEM [0018] Currently BCA sound requirements always achieved at the expense of com plicating the structure and increase of the weight and the wall thickness and accord ingly the cost of materials and labour. To improve soundproofing of a board by 6 dB in mass-controlled region it is necessary to either double the thickness of the board or use material that has twice more density. Majority of currently available boards and walls, which could provide builders with increased sound transmission loss are still bulky and expensive. The further improvement of the design of partition walls and achievement of required transmission loss and at the same time reducing the overall surface density of the boards, overall weight and thickness of the wall is an urgent task. SOLUTION TO PROBLEM [0019] The purpose of this invention is to design a board with increased transmission sound loss compared to the already known boards. Achieving this goal will ensure that the simplest Single Stud Wall Constructions could comply with the requirements of BCA and still remain at low cost, simplified design and decreased thickness of the wall.

5 [0020] Value of sound transmission loss R through boards or walls is described by Mass Law as: R=20 log (fm) - 47 dB, Equation 1 Where: f - frequency (Hz), m - mass per unit area (kg/m2). [0021] The Mass Law is effective in the frequency diapason where sound transmis sion loss is about 6dB for each doubling of mass per unit area. This frequency diapa son is limited by resonance frequency (fr) for low frequencies and coincidence fre quency (fcr) for high frequencies. The wider the frequency diapason where Mass Low is effective the higher wall transmission sound loss is. Extension of frequency diapason could be achieved by shifting fr towards lower frequencies and fcr to higher frequencies. To reach this goal it is necessary to increase the region of fre quencies between fr and fcr. Hence fr should be shifted to lower frequencies, and fcr to higher frequencies. [0022] For any building material with a given density p and Young's modulus E there is a dependency fcr on a layer thickness, which expressed as below: fcr = Kc / Equation 2 or d = f ~/p Equation 3 fcr Where: d - layer thickness, m; K - a constant = 0.556; C - speed of sound in air, m/sec; fcr - critical frequency, Hz; p - density, kg/m3; E - Young's modulus, Pa. [0023] By changing the thickness of a board fcr could be shifted to higher frequen cies. As result the range of frequencies where the Mass Law is effective will be in creased.

6 [0024] Considering the fact that physical characteristics of the board material such as thickness, critical frequency, surface density and Young's modulus define the value of STL it is easy to assume that there is an optimum layer thickness at which the maximum of STL is achieved. Innovative research proves the existence of the opti mum layer thickness which provides boards with the maximum value STL. At this layer thickness fcr is increased and frequency diapason is extended. [0025] Composite board that consists out of layers of optimum thickness will have the maximum STL. This assumption is true for any building material used for board de sign. The optimal layer thickness (OLT) at which the STL of the whole board reaches its maximum value is essential for each building material. The number of layers of a composite board is calculated with considerations of the desired STL value for the board as well as the number of boards for a whole wall construction. To reach maxi mum STL, a board has to be made as a multi-layer structure with optimum thickness of the layers. The total thickness of the board should be chosen from the considera tions of required STL. [0026] Therefore, first of all it is necessary to find out the OLT. The board consisting out of OLT layers will have the maximum STL value for any chosen type of material regardless of its surface density. For any value of the surface density of the selected material there is its own unique optimum thickness of a layer where the composite board has the maximum STL value. The number of layers inside a board is defined by the ratio of surface density of the board and the surface density of the layer. [0027] In order to confirm and find out the OLT, the series of tests had been done on the same thickness boards containing layers of different thicknesses. Multiplication of the number of layers by their thickness was always equal to the board thickness. Tests of the most acceptable lining building boards used in the construction industry were conducted by using of INSUL Software from Marshall Day Acoustics Ltd that can predict the performance of Rw and Ctr for building materials. Tests were con ducted for usual Single Stud Wall Constructions with lining boards which differed only by the number and thicknesses of layers. [0028] The test results are shown in tables 1-4 below.

7 TABLE 1 CSR Aquachek board, lining both sides of steel stud 76, p = 800kg/m3, E = 3.138GPa; Fcm = 26200 Hz kg/m2, insulation: 50 mm, 11 kg/m3 Bradford Gold R1.8 infill, board size: 2.7x 4 m, mass: 41.6 kg/m2. Linings, Rw/Rw+Ctr fr, Hz fcr, Hz Footprint, layers thickness, mm mm x layers number 26x1 50/45 57 1250 128 3x2 55/48 57 2500 128 8.7x3 58/48 57 3750 128 6.5x4 59/49 57 5000 128 5.2x5 54/48 57 6250 128 TABLE 2 Boral Standard boards, lining both sides of steel stud 76, p = 650kg/m3, E =1.683GPa, Fcm = 26200 Hz kg/m2, insulation: 50 mm, 11 kg/m3 Bradford Gold R1.8 infill, board size: 2.7x 4 m, mass: 33.8 kg/m2. Linings, Rw/Rw+Ctr fr, Hz fcr, Hz Footprint, layers thickness, mm mm x layers number 26x1 49/44 63 1600 128 13x2 54/46 63 3200 128 8.7x3 56/46 63 4800 128 6.5x4 56/46 63 6400 128 5.2x5 56/46 63 8000 128 TABLE 3 MgO board (magnesium oxide), lining both sides of steel stud 76, p=1 105 kg/m3, E = 5.9 GPa, Fcm =31000 Hz kg/m2, insulation: 50 mm, 11 kg/m3 Bradford Gold R1.8 infill, board size: 2.7x 4 m, mass: 53.0 kg/m2. Linings, Rw/Rw+Ctr fr, Hz fcr, Hz Footprint, layers thickness, mm x mm layer number 24 x1 49/46 51 1250 124 12 x2 57/51 51 2500 124 8 x3 63/53 51 3750 124 6 x4 62/53 51 5000 124 4.8x5 63/53 51 6250 124 8 TABLE 4 Soundcheck boards, lining both sides of steel stud 76, p = 1 000kg/m3, E = 6.129GPa, 26200Hz.kg/m2, insulation: 50 mm, 11 kg/m3 Bradford Gold R1.8 in fill, board size: 2.7x 4 m, mass: 52.0 kg/m2 (for 26 mm) and 64.0 kg/m2 (for 32 mm). Linings, Rw/Rw+Ctr fr, Hz fcr, Hz Footprint, layers thickness, mm x mm layer number 26x1 50/46 51 1000 128 13x2 56/51 51 2000 128 8.7x3 59/52 51 3000 128 6.5x4 56/51 51 4000 128 5.2x5 62/52 51 5000 128 32x1 50/46 46 800 140 16x2 57/53 46 1600 140 10.7x3 60/54 46 2400 140 8x4 62/55 46 3200 140 4x5 64/55 46 4000 140 [0029] Comparative results of Rw / Rw + Ctr for walls with single-layer and multi-layer boards with optimum of layer thickness are shown in table 5. TABLE 5 Comparative results of Rw / Rw + Ctr for walls with single-layer and multi-layer boards with optimum of layer thickness. Wall lining Board thick- Rw/Rw+Ctr Rw/Rw+Ctr Increasing material ness, mm index % SSR 26x1 50/45 0/0 100/100 Aquachek boards 6.5x4 59/49 9/4 118/109 Mag board 24 x1 49/46 0/0 100/100 (magnesium oxide) 4.8x5 63/53 14/7 129/115 Soundcheck 26x1 50/46 0/0 100/100 boards 5.2x5 62/52 12/6 124/113 32x1 50/46 0/0 100/100 6.4x5 64/55 14/9 128/120 9 [0030] During the first stage the tests were conducted to compare sound characteris tics of single layer and multi-layer boards of the same thickness. The innovative boards were compared versus well known in building industry plasterboards such as: Boral Soundstop, CSR Fyrcheck, CSR Fyrcheck, CSR Soundcheck Gypsum plas terboard and Lightweight concrete. [0031] To confirm industrial applicability and embodiments of present invention tests were conducted for a wall construction shown in Figure 2. On this stage Rw and Ctr of walls were measured for both types of construction to compare the same thickness of wall construction using two single layer boards and offered composite multi-layer boards. Two single lining boards were chosen from most commonly used brands in building industry. Both types of boards have been used as lining board on steel studs. ADVANTAGEOUS EFFECTS OF THE PRESENT INVENTION [0032] For the most of the building materials used as multi-layer lining board for parti tion walls there is the optimal thickness of the layer at which sound transition loss of a board consisting of these layers reach maximum value. Test results represented in Figures 4-11 definitely confirmed the presence and the possibility of determining the optimal thickness of the layer at which sound transition losses reach maximum value. [0033] It is quite evident that Rw of composite boards exceeds Rw of single boards by 3-5 units. This corresponds to reduced intensity of sound level by 5-6 dB. Using composite boards in the walls lining will reduce the sound level roughly by half. [0034] In addition, a board consisting out of several layers has significantly greater sound absorption coefficient than a single-layer board and increases STL. Also addi tional increase of the coefficient of sound absorption in the composite board could be achieved by alternative arrangements of layers with the different densities. [0035] It is necessary to note that a lot of plasterboards used in building industries have thickness of 13mm and 16mm, that does not conform to the optimal thickness in terms of the max of STL value.

10 [0036] The Single Stud Wall Constructions lined by composite boards with optimum layer thickness compared with lined by single-layers boards have Rw increased up to 28% and Rw + Ctr up to 20%. [0037] Composite board design provides additional increase of STL due to the inher ent lower stiffness as compared with single-layered board. Reducing the stiffness provides a shift of fr towards lower frequencies, and thus extends the frequency range where the Mass Low law is observed. [0038] Results of the tests confirmed that walls with innovative composite boards in comparison with the well known and used in building industry boards achieve: - Greater transmission sound loss Rw/Rw+Ctr, reduced wall thickness, and reduced construction cost (Table 6). - Addition of extra living space (+m2) due to lower thickness if Innovative composite walls are using instead traditional walls. (Table7). TABLE 6 Comparative assessment of CSR Walls and Innovative Single Stud Walls. Type of Wall construction Weight, Wall Rw/Rw+Ctr, Cost, % from kg/m2 thick- unit Base Single ness, mm Stud Base Single Stud CSR 080 50.0 140 52/44 100 Staggered Stud Wall CSR 175 42.0 202 58/50 120 Double Stud Wall CSR 275 42.0 252 59/51 130 Resilient Mount Wall CSR 061 42.0 156 58/50 130 Innovative Single Stud Wall 53.0 124 63/53 80 TABLE 7 Additional living space (+m2) if Innovative Composite Walls (thickness 124 mm, weight 38.4 kg/m2) are using instead traditional walls.

11 Type of Dif- Extra living space S, m2 Wall feren Constr. ce in 25 50 100 150 225 450 900 9900 thick- m2 m2 m2 m2 m2 m2 m2 m2 ness of walls, m Stagger 0.078 +2.34 +3.51 +6.24 +9.0 +12.9 +24.6 +47.2 +517 ed Stud Wall CSR 175 Double 0.128 +2.3 +2.56 +10.2 +14.7 +21.1 +40.3 +77.4 +852 Stud Wall CSR 275 Resilient 0.032 +0.96 +1.4 +2.6 +3.7 +5.28 +10.1 +19.4 +213 Mount Wall CSR 061 0.032 1 1 1 1 1 1 1 1 1 1 [0039] Advantage of Invention lies in the fact that: * Definitely confirmed the presence and possibility of determining the optimal thick ness of the layer at which sound transition losses reach maximum value. * Existence of the optimal thickness of the layer at which sound transition loss of a board consisting of these layers reach maximum value for the most of building ma terials used as multi-layer lining boards for partition walls * Established method how to determine and identify the optimal thickness of the layer of composite board for maximum sound transition losses. . The Single Stud Wall Constructions lined by composite boards with the optimum layer thickness compared with lined by single-layers boards have Rw increased up to 28% and Rw + Ctr up to 20%. . Rw of composite boards exceeds Rw of single boards by 3-5 units. This corre sponds to reduced intensity of sound level by 5-6 dB. Lining of walls by composite boards correspondingly allows to reduce the sound penetration by approximately 50% 12 * Innovative boards achieve increased transmission sound loss Rw/Rw+Ctr, reduced weight, wall thickness, and cost. * Using innovative boards in building industry instead traditional walls provides addi tional living space (+m2). DESCRIPTION OF EMBODIMENTS [0040] Embodiments of a composite board and a partition wall in accordance with the present invention will be described by way of example only with reference to the ac companying drawings. Figure 1 is a composite board with gasket material between layers. Figure 2 is an embodiment of single metal stud partition wall including the in novative composite boards. Figure 3 is a view of the composite board locations into partition wall. Figures 1 -11 shown examples of embodiments of boards and walls constructed from widely using building materials. [0041] Referring to Figures 1, composite board 10 containing layers 11 is shown with only three layers. Every layer has a value of surface density optimized for used mate rial by STL. Layers of composite board are lightly fixed together mechanically by screw or with using gasket or suitable adhesive material 12. Any chosen a way of fix ing must ensure a layering passage the sound waves through the thickness of the board. As gasket material can be a paper or the like. [0042] Figure 2 is perspective view of a Single Stud Wall 20. It is the embodiment of the part of partition wall area of 6.48 m2, size of wall is 3600 x 1800 x 123 mm. Shown wall contents three 75mm Steel Stud 25, 70.0 mm Bradford Gold R1.8 insu lation 26 and four assemblies of composite boards. Every board comprises three lay ers of magnesium oxide material. [0043] All board assemblies represented in Figure 3 have the same area. First of four assemblies consists out of 9 full size composite boards 1200x600x12 mm. In the second assembly the boards are shifted by one-fourth of the length and width of the full board size. Accordingly for third and fourth assemblies the boards are shifted by half and three-fourths of board size in both directions. Positioning of the boards loca tion in every assembly allows avoiding an overlap of the liner joints between boards.

13 As the result the assembly 30 prevents the passage of the sound waves 31 along a straight line through the matching joints of the boards. [0044] Figures 4 - 8 show a functional dependency of Sound Reduction Index from the sound frequency for single-layer boards (1) and embodiment of multi-layer com posite boards (2) with the same board thicknesses. [0045] Figure 4 represents Sound Transmission Loss of a single-layer board (1): 1 x 20.0 mm Boral Soundstop plasterboard, measurement result: Rw = 30, Ctr = -3 and composite board (2): 5 x 4.0 mm Boral Soundstop plasterboard, measurement result: Rw = 34, Ctr = -4 with the same board thicknesses of 20 mm. [0046] Figure 5 represents Sound Transmission Loss of a single-layer board (1): 1 x 16.0 mm CSR Fyrcheck plasterboard, measurement result: Rw =29, Ctr= -3 and composite board (2): 4 x 4.0 mm CSR Fyrcheck plasterboard, measurement result: Rw = 32, Ctr= -4 with the same board thicknesses of 16 mm. [0047] Figure 6 represents Sound Transmission loss of a single-layer board (1): x 16.0 mm CSR Soundchek plasterboard, measurement result: Rw = 29, Ctr= -2 and composite board (2): 4 x 4.0 mm CSR Soundchek plasterboard, measurement result: Rw=34, Ctr= -4 with board thicknesses of 16 mm. [0048] Figure 7 represents Sound Transmission Loss of a single-layer board (1): 1 x 16.0 mm Gypsum plasterboard, measurement result: Rw= 28, Ct r= -2 and composite board (2): 4 x 4.0 mm Gypsum plasterboard, measurement result: Rw =31, Crt = -4 with the same board thicknesses of 16 mm. [0049] Figure 8 represents Sound Transmission Loss of a single-layer board (1): 1 x 100.0 mm Lightweight concrete, measurement result: Rw = 44, Ctr= -3 and compo site board (2): 5 x 20.0 mm Lightweight concrete, measurement result: Rw = 49, Ctr= -2 with the same board thicknesses of 100 mm.

14 [0050] Figures 9-11 show Sound Transmission Loss of walls containing on both sides of the stud two single plasterboards (1) and embodiment walls containing the composite multi-layer boards (2) with the same wall thickness. [0051] Figure 9 represents Sound Transmission Loss of walls containing the single boards (1) and composite multi-layer boards (2) of CSR Soundcheck plasterboards. Common characteristics of Walls: Linning material of CSR Soundcheck plasterboard, density= 1000 kg/m3, Young Modulus= 6.129 Gpa, surface density = 48.Okg/m2. In sulation material is of 70.0 mm Bradford Gold R1.8. Wall thickness = 123mm. Steel Stud Wall 1: 2 x 12.0 mm CSR Soundcheck plasterboard +75 Steel Stud with insulation material + 2 x 12.0 mm CSR Soundcheck plasterboard. Measurement re sult: Rw = 56, Ctr = - 6. Steel Stud Wall 2: 8 x 3.0 mm CSR Soundcheck plasterboard +75 Steel Stud with insulation material + 8 x 3.0 mm CSR Soundcheck plasterboard. Measurement re sult: Rw= 61, Ctr = -10. [0052] Figurel 0 represents Sound Transmission Loss of walls containing the single boards (1) and composite multi-layer boards (2) of plasterboards of MgO (magnesi um oxide). Common characteristics of Walls: Linning material of MgO board, density = 1105 kg/m3, Young Modulus= 5.907 Gpa, surface density = 53.Okg/m2. Insulation material is of 70.0 mm Bradford Gold R1.8. Wall thickness = 123mm. Steel Stud Wall 1: 2 x 12.0 mm MgO board + 75 Steel Stud with insulation material + 2 x 12.0 mm MgO board. Measurement result: Rw=57, Rw+Ctr =51. Steel Stud Wall 2: 6 x 4.0 mm MgO board + 75 Steel Stud with insulation material + 6 x 4.0 mm MgO Board. Measurement result: Rw=63, Rw+Ctr = 53. [0053] Figure 11 represents Sound Transmission Loss of walls containing the single boards (1) and composite multi-layer boards (2) of CSR Aquacheck plasterboards. Common characteristics of Walls : CSR Aquacheck plasterboard, density= 800 kg/m3, Young Modulus= characteristics 3.138 Gpa, surface density = 51.2kg/m2. In sulation material is of 70.0 mm Bradford Gold R1.8. Wall thickness = 139mm. Steel Stud Wall 1: 2 x 16.0 mm CSR Aquacheck plasterboard +75 Steel Stud with insulation material + 2 x 16.0 mm CSR Aquacheck plasterboard. Measurement re- 15 suit: Rw= 56, Ctr=-5. Steel Stud Wall 2: 8 x 4.0 mm CSR Aquacheck plasterboard + 75 Steel Stud with in sulation material + 8 x 4.0 mm CSR Aquacheck plasterboard. Measurement result: Rw = 62, Ctr=-1 0.

Claims (5)

1. Composite board that provides a high sound transmission loss and an attainment of acceptable level of airborne sound by utilizing sets of different or the same surface density layers at which the critical frequency of the board increases and shifts to higher frequency and the frequency band where the Mass Law effect is significantly increased.

2. Every layer of composite board according to claim 1 has the surface density optimized by maximum criteria Rx- sound reduction index and the thickness that provides a required shift of a critical frequency.

3. The number of layers inside the composite board according to claim 1 is defined by the ratio of surface density of the board and the surface density of the layer to provide the maximum Rx.

4. Layers of the composite board according to claim 1 are lightly fixed together mechanically by screws or by gaskets or suitable adhesive materials, ensuring layer by layer transit of the sound waves through the thickness of the board.

5. Composite boards according to claim 1 situated inside of the partition walls are installed in assemblies therefore positioning of the boards in every assembly allows avoiding an overlap of the liner joints between boards.