Noise diffusion preventing device

Abstract

The application provides a noise diffusion-preventing device, which is assembled in a building cavity structure and comprises an inner wall for forming an irregular inner cavity, an air inlet pipe and an air outlet pipe located at different sides and communicating the building cavity structure and the inner cavity, and sound-absorbing cotton attached to inner walls of the air inlet pipe and the air outlet pipe, an inner top covering the top of the inner wall, a floating building ground laid in the inner cavity, a plurality of lightweight diffusion plates of different sizes installed on the inner wall of the inner wall or the inner top and used for guiding the diffusion of middle and low frequency sound waves to redistribute the reflection path of the middle and low frequency sound waves, and a vibration isolation assembly arranged in the gap between the inner cavity and the building cavity structure to form a suspended diffusion cavity. The above-mentioned scheme is used to form a suspended room-in-room acoustic cavity, and the lightweight diffusion plates are arranged flexibly and specifically, so that the formation probability of middle and low frequency standing waves can be effectively reduced, the excessive concentration of sound energy in corners or local areas can be avoided, and the redistribution of the reflection path of middle and low frequency sound waves can be realized.

Description

Technical Field

[0001] This invention relates to the technical field of noise diffusion treatment devices, and in particular to a noise diffusion prevention device. Background Technology

[0002] The core principle of existing noise acoustic wave acquisition devices is to create a diffusion environment with uniform energy density and random propagation direction through multiple reflections of sound waves indoors, achieving statistical homogeneity of the sound field. This provides standardized and repeatable experimental conditions for noise source characteristic measurement, material acoustic performance evaluation, and acoustic environment simulation. However, in practical applications, it has been found that existing noise acoustic wave acquisition devices have good reflection effects on high-frequency sound waves, but for mid- and low-frequency sound waves, they are prone to coupling with the device boundary, forming standing waves, reflection superposition, or resonance, resulting in poor reflection effects. Therefore, the applicant proposes the technical solution of this invention to achieve anti-diffusion treatment of mid- and low-frequency sound waves. Summary of the Invention

[0003] In view of the above-mentioned deficiencies of the prior art, the purpose of the present invention is to provide a noise diffusion prevention device to achieve noise diffusion prevention treatment of mid- and low-frequency sound waves.

[0004] To achieve the above and other related objectives, the present invention provides the following technical solution:

[0005] A noise diffusion prevention device, assembled within a building cavity structure, includes:

[0006] An inner wall is constructed to form an irregular inner cavity. An air inlet pipe and an air outlet pipe located on different sides are provided connecting the building cavity structure and the inner cavity. The inner walls of the air inlet pipe and the air outlet pipe are covered with sound-absorbing cotton.

[0007] An inner ceiling covering the top of the inner wall;

[0008] A floating floor laid in the inner cavity;

[0009] Several lightweight diffuser plates of different sizes are installed on the inner wall or the inner ceiling to guide the diffusion of mid- and low-frequency sound waves to redistribute the reflection path of mid- and low-frequency sound waves; the lightweight diffuser plate includes a diffuser section with an internal labyrinth structure and a mounting section fixedly connected to the back of the diffuser section and magnetically connected to the inner wall or the inner ceiling.

[0010] Vibration isolation components are installed in the gap between the inner cavity and the building cavity structure to form a suspended diffusion cavity with the inner wall, inner ceiling and floating floor.

[0011] To achieve the above technical solution, irregular inner walls and ceilings are constructed, which, together with a floating floor, form an inner cavity. This cavity, together with the building structure cavity, creates a "floating room-within-a-room" acoustic chamber. This not only effectively reduces the probability of mid-to-low frequency standing waves, but the design of the floating floor and vibration isolation components also prevents the sound source signal from being coupled with external vibrations or building structure noise. In addition, the lightweight diffuser plates installed on the inner walls and ceiling, especially at the wall junctions, effectively prevent excessive concentration of sound energy in corners or local areas, achieving a redistribution of the reflection path of mid-to-low frequency sound waves. The lightweight diffuser plates are designed to be flexibly customized for installation as needed, allowing for targeted placement to optimally guide the uniform reflection of the mid-to-low frequency sound field.

[0012] Furthermore, the floating ground includes an elastic cushion layer, a concrete protective layer, and a reflective layer laid in sequence.

[0013] To achieve the above technical solution, the floating ground design involves laying an elastic pad directly on the floor to effectively isolate low-frequency vibrations and structural noise from the floor, thus avoiding sound source interference; a concrete protective layer and a reflective layer are laid on the elastic pad to jointly construct a highly reflective hard interface.

[0014] Furthermore, the elastic pad layer includes a spring and glass wool boards connected to both ends of the spring.

[0015] To achieve the above technical solution, a "sandwich" structure of glass wool board-spring-glass wool board is adopted. This effectively utilizes the auxiliary sound absorption, buffer protection and stress dispersion characteristics of glass wool board, while the spring provides excellent low-frequency vibration isolation performance, thereby effectively blocking vibration and structural noise interference from the building structure.

[0016] Furthermore, the surface of the diffuser is stepped.

[0017] To achieve the above technical solution, the stepped surface of the diffuser achieves the effect of "diffusing and dispersing sound energy outward" through staggered geometric steps. Combined with the labyrinthine structure of the inner cavity, it "guides inward" and "interferes and disrupts" the propagation path of mid- and low-frequency sound waves through the tortuous and multi-angled cavity. The combined effect of the stepped surface and the labyrinthine structure of the inner cavity on mid- and low-frequency sound waves achieves a balanced reflection effect of "guiding inward and diffused outward".

[0018] Furthermore, both the inner wall and the inner ceiling are made of aluminum honeycomb panels, and the interlayer of the aluminum honeycomb panels is provided with thin galvanized steel sheets.

[0019] To achieve the above technical solution, aluminum honeycomb panels are used as the material for the interior walls and ceiling. This fully utilizes the lightweight, high-strength, high-rigidity, and structurally stable characteristics of aluminum honeycomb panels, as well as their ease of modular processing and on-site assembly. This significantly reduces the difficulty of direct indoor construction within the building structure and improves operational feasibility. Furthermore, the lightweight diffuser plate and the reflective surface of the aluminum honeycomb panel can complement each other, effectively improving the uniformity and diffusion of the mid-to-low frequency sound field.

[0020] Furthermore, the mounting portion includes a flexible mounting foot fixedly mounted on the back of the diffuser portion, and a strong magnet fixedly mounted on the mounting foot.

[0021] To achieve the above technical solution, a strong magnet is used to magnetically connect the lightweight diffuser plate to the inner wall or ceiling by placing a thin galvanized steel plate in the interlayer of the aluminum honeycomb panel. The magnetic connection can be flexibly arranged as needed to achieve the optimal guiding effect through the arrangement of the diffuser plate. At the same time, the design of the flexible mounting feet allows the lightweight diffuser plate to be placed in corners where sound waves are prone to excessive concentration, such as corners.

[0022] Furthermore, the inner wall is wrapped with an elastic sealing gasket at the contact edge with the air inlet pipe and the air outlet pipe.

[0023] To achieve the above technical solution, the elastic sealing gasket has elastic and damping properties, which can reduce the transmission of vibration from the pipe to the aluminum honeycomb panel and absorb vibration energy. At the same time, it also helps to improve the overall airtightness of the pipe and prevent air leakage.

[0024] Furthermore, a reinforcing ring is provided within the interlayer of the aluminum honeycomb panel, surrounding the air inlet pipe and the air outlet pipe.

[0025] The above technical solution strengthens the ring and enhances the overall stiffness and load-bearing capacity of the structure around the opening.

[0026] Furthermore, the vibration isolation component adopts a spring-damping composite structure.

[0027] The above technical solution achieves low-frequency vibration isolation support through springs and suppresses resonance and dissipates vibration energy through damping materials, thereby achieving flexible isolation between the aluminum honeycomb panel and the building structure and blocking the transmission path of low-frequency vibration and structural noise.

[0028] Furthermore, the diffusion section is made of medium-density fiberboard.

[0029] The above technical solution uses medium-density fiberboard (MDF) as the substrate, making full use of the advantages of MDF, such as light weight, easy processing, low cost, and easy installation and adjustment. Furthermore, after modular design, it can be flexibly arranged in a targeted manner.

[0030] As described above, the noise diffusion prevention device provided by the present invention has the following beneficial effects:

[0031] This invention provides a noise diffusion prevention device, assembled within a building cavity structure, comprising: an inner wall enclosing an irregularly shaped inner cavity; an air inlet pipe and an air outlet pipe located on different sides connecting the building cavity structure and the inner cavity; the inner walls of the air inlet pipe and the air outlet pipe being lined with sound-absorbing cotton; an inner ceiling covering the top of the inner wall; a floating floor laid within the inner cavity; and several lightweight diffusion plates of varying sizes installed on the inner walls or inner ceiling to guide the diffusion of mid-to-low frequency sound waves and redistribute the reflection paths of the mid-to-low frequency sound waves; the lightweight diffusion plates include an internal structure... The labyrinthine structure includes a diffuser section and an installation section fixedly connected to the back of the diffuser section and magnetically connected to the inner wall or ceiling. Vibration isolation components are installed in the gap between the inner chamber and the building cavity structure to form a suspended diffuser cavity with the inner wall, ceiling, and floating floor. The above schemes together constitute a "suspended room-within-a-room" acoustic cavity. With the targeted and flexible arrangement of lightweight diffuser plates, the probability of mid-to-low frequency standing waves can be effectively reduced, and excessive concentration of sound energy in corners or local areas can be avoided, thereby achieving the redistribution of the reflection path of mid-to-low frequency sound waves. Attached Figure Description

[0032] Figure 1 An exemplary top view of the internal structure of a specific embodiment of the noise diffusion prevention device of this application is shown.

[0033] Figure 2 An exemplary schematic diagram of a specific embodiment of the aluminum honeycomb panel of this application is shown.

[0034] Figure 3 An exemplary schematic diagram of a specific embodiment of the floating ground of this application is shown.

[0035] Figure 4 An exemplary cross-sectional view of a specific embodiment of the diffuser plate of this application is shown.

[0036] Figure 5 An exemplary schematic diagram showing one specific embodiment of the inner cavity of the labyrinth structure of the diffuser plate of this application.

[0037] Figure 6 An exemplary schematic diagram showing an application example of the noise diffusion prevention device of this application is provided.

[0038] Attached image captions:

[0039] 1. Wall; 2. Floor; 3. Interior wall; 4. Floating floor; 41. Elastic padding layer; 411. Spring; 412. Glass wool board; 42. Concrete protective layer; 43. Reflective layer; 5. Aluminum honeycomb panel; 51. Aluminum alloy panel; 52. Aluminum honeycomb core; 6. Thin galvanized steel sheet; 7. Air inlet duct; 8. Air outlet duct; 9. Diffuser plate; 91. Diffuser section; 92. Mounting section; 921. Mounting foot; 922. Strong magnet; 10. Spring-damping composite structure; 11. Elastic sealing gasket; 12. Rotary table; 13. Air source chamber; 14. Air duct chamber; 15. Inner chamber. Detailed Implementation

[0040] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0041] Please see Figures 1 to 6 It should be understood that the structures, proportions, sizes, etc., illustrated in the accompanying drawings are merely for illustrative purposes to aid those skilled in the art and to facilitate understanding and reading. They are not intended to limit the scope of the invention and therefore have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to size, without affecting the effectiveness and purpose of the invention, should still fall within the scope of the technical content disclosed in this invention. Furthermore, the terms such as "upper," "lower," "left," "right," "middle," and "one" used in this specification are merely for clarity and not intended to limit the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention's implementation.

[0042] Please see Figure 1 This invention provides a noise diffusion prevention device, which is installed within a building cavity structure enclosed by a wall 1, a ceiling, and a floor 2; for details, please refer to [link to relevant documentation]. Figure 1 and Figure 2 The noise diffusion prevention device includes an inner wall 3 constructed using aluminum honeycomb panels 5 to form an irregular internal cavity. The outer two layers of the aluminum honeycomb panels 5 are aluminum alloy panels 51, and the middle layer is an aluminum honeycomb core 52, together forming a strong and stable "sandwich structure." The aluminum honeycomb panels 5 can be modularly processed through CNC precision cutting, bending, stamping, drilling, and other processes, and are easy to assemble on-site, thus significantly reducing the difficulty of construction within the building's cavity structure.

[0043] For details, please refer to Figure 1In this embodiment, the irregular inner cavity constructed from aluminum honeycomb panels 5 has no parallel inner walls 3, and the lengths of adjacent inner walls 3 forming the inner cavity are in a non-integer ratio. This irregular inner cavity can disperse the regular reflection paths of sound waves, thereby effectively suppressing standing waves and improving the uniformity of the sound field. The volume V of the constructed irregular inner cavity strictly conforms to the international standard V≥4λ. 3 Where λ is the wavelength of the lowest frequency sound wave to be measured. In this embodiment, the volume of the irregular inner cavity is 400 m³.

[0044] Continue reading Figure 1 and Figure 3 A floating floor 4 is laid on the floor 2 of the irregular interior cavity. Specifically, the floating floor 4 includes an elastic pad 41, a concrete protective layer 42, and a reflective layer 43 laid sequentially. In this embodiment, the elastic pad 41 adopts a composite structure of glass wool board 412-spring 411-glass wool board 412, that is, the upper and lower layers are both glass wool boards 412, and the two sides of the glass wool boards 412 are connected by springs 411 at both ends. This structure can effectively utilize the auxiliary sound absorption function of the glass wool board 412, and together with the springs 411, provide excellent low-frequency vibration isolation performance, effectively blocking vibrations and structural noise interference from the building structure. In this embodiment, the reflective layer 43 is a smooth ceramic tile laid on the surface of the concrete protective layer 42. The smooth ceramic tile and the concrete protective layer 42 construct a highly reflective hard reflective surface. In other embodiments, the reflective layer 43 can also be a wooden floor or aluminum alloy plate or other materials with high reflective properties laid on the concrete protective layer 42.

[0045] Continue reading Figure 1 and Figure 2 The top of the inner wall 3 is covered by an inner ceiling made of aluminum honeycomb panels 5. A thin galvanized steel plate 6 is provided in the interlayer between the two layers of aluminum alloy panels 51 on the outside of the aluminum honeycomb panels 5 that make up the inner wall 3 and the inner ceiling. The thin galvanized steel plate 6 can strengthen the aluminum honeycomb panels 5 on the one hand, and compensate for the non-magnetic nature of the aluminum honeycomb panels 5 on the other hand.

[0046] Continue reading Figure 1 Vibration isolation components are installed in the gap formed between the irregular inner cavity and the building cavity structure. In this embodiment, the vibration isolation components adopt a spring-damping composite structure. The spring-damping composite structure realizes the flexible isolation between the aluminum honeycomb panel 5 and the building structure. The spring material provides low-frequency vibration isolation support, and the damping material suppresses resonance and dissipates vibration energy. The combination of the two achieves the purpose of blocking the transmission path of low-frequency vibration and structural noise.

[0047] The inner cavity 15 formed by the inner wall 3, inner ceiling and floating ground 4 in this technical solution, together with the building cavity structure formed by the wall 1, floor 2 and ceiling, constitutes a "suspended room within a room" structure, which completely decouples the inner cavity 15 from the outer building structure, thereby blocking the transmission of low-frequency vibrations to the inner cavity 15 through the solid structure, and has the effect of vibration decoupling and noise shielding.

[0048] Continue reading Figure 1 , Figure 4 and Figure 5 Several lightweight diffusion plates 9 of varying sizes are installed on the inner wall 3 and the inner ceiling as needed. Each lightweight diffusion plate 9 includes a diffusion section 91 with a stepped surface and a mounting section 92 installed on the back of the diffusion section 91. Specifically, in this embodiment, the diffusion section 91 is made of medium-density fiberboard (MDF). MDF has a uniform overall structure and can be precisely manufactured using CNC engraving, laser cutting, etc., to create the required diffusion section 91 structure. For example, in this embodiment, the diffusion section 91 uses MDF as the substrate, with a stepped surface and a labyrinthine internal cavity. Furthermore, MDF has relatively low raw material and processing costs, offering significant economic advantages. Specifically, in this embodiment, the diffusion section 91 uses MDF as the substrate, first machining the highest central truncated cone, then machining truncated cones of decreasing height outwards, forming a stepped structure; then, staggered, curved grooves are carved inwards from the surface of the truncated cones. (See reference...) Figure 5 The grooves form a maze-like interior cavity in the front view. The staggered stepped surface, combined with the labyrinthine internal structure, creates a winding, multi-angled cavity that achieves the effect of "diffusion outwards and guidance inwards".

[0049] The mounting part 92 includes a mounting foot 921 fixedly connected to the back of the diffuser part 91 and a strong magnet 922 fixedly connected to the mounting foot 921. Specifically, in this embodiment, the mounting foot 921 is made of rubber material, which is fixedly connected to the medium-density fiberboard by screws. The mounting foot 921 has a mounting groove, in which the strong magnet 922 is embedded. The strong magnet 922 is bonded to the rubber with strong adhesive. In this embodiment, the strong magnet 922 is a neodymium iron boron magnet. The mounting foot 921 is made of rubber material, which has good deformability and can adapt to installation at the corner of the wall.

[0050] Specifically, when installing the diffuser plate 9, it is placed in the desired position. The strong magnet 922 of the mounting part 92 of the diffuser plate 9 forms a magnetic connection with the thin galvanized steel plate 6, thereby connecting the diffuser plate 9 to the inner wall 3 or the inner ceiling. Furthermore, the required number, size, and position of the diffuser plates 9 can be customized to achieve a good fit between the diffuser plate 9 and the inner wall 3, inner ceiling, and floating floor 4. Moreover, the rubber mounting feet 921 allow the diffuser plate 9 to be installed in corners or other hard-to-reach locations, effectively preventing excessive concentration of sound energy in localized areas.

[0051] The building cavity structure and the irregular inner cavity are connected by an air inlet pipe 7 and an air outlet pipe 8. An elastic sealing gasket 11 is wrapped around the abutting edge of the air inlet pipe 7 and the air outlet pipe 8. In this embodiment, the elastic sealing gasket 11 is a rubber sealing gasket. At the same time, in order to strengthen the fixing of the opening of the aluminum honeycomb panel 5, a reinforcing ring is provided around the abutting opening of the air inlet pipe 7 and the air outlet pipe 8. In this embodiment, the reinforcing ring is a metal steel ring set in the interlayer of the aluminum honeycomb panel 5.

[0052] Furthermore, to prevent external noise from entering through the pipes, sound-absorbing cotton is attached to the inner walls of the air inlet pipe 7 and the air outlet pipe 8.

[0053] The noise diffusion prevention device provided in this application can be applied to performance verification in various simulated real environments, such as testing and verification of mid-to-low frequency sound bands in automobiles, aerospace, industrial workshops, and buildings and homes.

[0054] This application uses the performance verification of an air conditioning temperature and humidity control device as a specific application case for explanation. The main sound source of the air conditioning temperature and humidity control device is concentrated in the mid-to-low frequency range. In order to verify whether the equipment meets the design noise index, to troubleshoot problems in installation or system configuration, and to meet the needs of equipment optimization design and quality improvement, it is necessary to collect the sound source waves generated by the air conditioning temperature and humidity control device during operation. (See reference...) Figure 6An air inlet duct 7 extends through the duct chamber 14 to the air source chamber 13. The air source chamber 13, the duct chamber 14, and the wall 1 are located within the interior of the outer building structure. A spring-damping composite structure is installed between the duct chamber 14 and the outer building structure. The gap between the wall 1 and the outer building structure forms an air duct. A variable frequency fan is installed in the air source chamber 13, which simulates the air volume of the usage scenario and delivers it through the air inlet duct 7. Elastic vibration damping pads are installed at the connection points between the air inlet duct 7 and the duct chamber 14 and the air source chamber 13 to eliminate vibrations caused by rigid connections. Vibration and noise are transmitted to the air inlet pipe 7. The open end of the air inlet pipe 7 located in the inner chamber 15 is connected to the air conditioning temperature and humidity control device to be tested. A rotating platform 12 is set on the floating ground 4, and a noise detector is installed on the rotating platform 12. The noise detector installed on the rotating platform 12 collects the noise of the air conditioning temperature and humidity control device under different air volume working conditions reflected by the inner chamber 15. The air in the inner chamber 15 flows to the air duct through the air outlet pipe 8 and then flows back to the air source chamber 13 through the air duct. On the one hand, it balances the air pressure inside and outside the inner chamber 15, and on the other hand, it simulates the ventilation usage scenario.

[0055] This practical application effectively isolates the propagation path of rigid vibration by constructing a "suspended room-within-a-room" structure. Furthermore, the irregular inner cavity 15 built with aluminum honeycomb panels 5 and the diffuser plates 9 arranged as needed, which form a labyrinth structure within the inner cavity, guide the sound waves of various frequency bands generated by the air conditioning temperature and humidity control device, effectively improving the noise prevention and diffusion of the air conditioning temperature and humidity control device.

[0056] The noise diffusion prevention device provided in this application is directly installed inside the building cavity structure and together with the building cavity structure, forms a "suspended room-within-a-room" acoustic cavity. With the targeted and flexible arrangement of lightweight diffusion plates, it effectively reduces the probability of the formation of mid- and low-frequency standing waves. At the same time, the flexible arrangement of the lightweight diffusion plates can effectively avoid excessive concentration of sound energy in corners or local areas, thereby achieving the redistribution of the reflection path of mid- and low-frequency sound waves.

[0057] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A noise diffusion prevention device, assembled within a building cavity structure, characterized in that, include: An inner wall (3) is erected to form an irregular inner cavity, wherein the irregular inner cavity is an inner cavity without parallel inner walls (3) and the lengths of the adjacent inner walls (3) constituting the inner cavity are in a non-integer ratio; The building cavity structure and the inner cavity are connected by an air inlet pipe (7) and an air outlet pipe (8) located on different sides. The inner walls of the air inlet pipe (7) and the air outlet pipe (8) are covered with sound-absorbing cotton. An inner ceiling covering the top of the inner wall (3); A floating floor (4) laid in the inner cavity; Several lightweight diffuser plates (9) of different sizes are installed on the inner wall (3) or the inner ceiling to guide the diffusion of mid- and low-frequency sound waves to redistribute the reflection path of mid- and low-frequency sound waves; the lightweight diffuser plate (9) includes a diffuser part (91) with an internal labyrinth structure and a mounting part (92) fixedly connected to the back of the diffuser part (91) and magnetically connected to the inner wall (3) or the inner ceiling. Vibration isolation components are installed in the gap between the inner cavity and the building cavity structure to form a suspended diffusion cavity with the inner wall, inner ceiling and floating floor.

2. A noise diffusion prevention device according to claim 1, characterized in that, The floating ground (4) includes an elastic cushion layer (41), a concrete protective layer (42), and a reflective layer (43) laid in sequence.

3. A noise diffusion prevention device according to claim 2, characterized in that, The elastic pad (41) includes a spring (411) and glass wool boards (412) connected to both ends of the spring (411).

4. A noise diffusion prevention device according to claim 1, characterized in that, The surface of the diffuser (91) is stepped.

5. A noise diffusion prevention device according to claim 1, characterized in that, The inner wall (3) and the inner ceiling are both made of aluminum honeycomb panels (5), and the interlayer of the aluminum honeycomb panels (5) is provided with thin galvanized steel plates (6).

6. A noise diffusion prevention device according to claim 5, characterized in that, The mounting portion (92) includes a flexible mounting foot (921) fixedly mounted on the back of the diffuser portion (91), and a strong magnet (922) fixedly mounted on the mounting foot (921).

7. A noise diffusion prevention device according to claim 5, characterized in that, The inner wall (3) is wrapped with an elastic sealing gasket (11) at the contact edge with the air inlet pipe (7) and the air outlet pipe (8).

8. A noise diffusion prevention device according to claim 7, characterized in that, The aluminum honeycomb panel (5) has a reinforcing ring inside its interlayer that surrounds the air inlet pipe (7) and the air outlet pipe (8).

9. A noise diffusion prevention device according to claim 1, characterized in that, The vibration isolation component adopts a spring-damping composite structure.

10. A noise diffusion prevention device according to claim 1, characterized in that, The diffuser (91) is made of medium-density fiberboard.

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