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The difference between the sound-absorbing materials and insulation materials

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The difference between the sound-absorbing materials and insulation materials

Data:2016-03-07 00:00 Source:http://www。rywfjx。com Click:

Interior decoration has become an independent industry, large and small decoration decoration company like springing up everywhere everywhere. Many decoration companies, with new styles, new materials, new technology to bring a new look interior architectural decoration, reached a new level.

Room acoustics design is a discipline system, involves a broader, it only makes a brief introduction to the knowledge of the materials and structure and interior decoration related absorption and sound insulation, decoration and owners hope to have acoustic materials and structures understand it, to understand why the acoustic design for this kind of treatment, so that the decoration works to achieve the perfect unity in the aesthetic and acoustic requirements。

1. Basic concepts of sound-absorbing and sound-proofed

It must first clear sound absorption and sound insulation are two completely different concepts of acoustics. Sound-absorbing acoustic propagation refers to one side interface, the sound can be a part of the boundary surface reflection (or scattering), part of the sound energy is absorbed boundary surface (not considered here absorbed by the medium of propagation in the medium), including sound waves within the boundaries of the material is consumed into heat or vibration can be transferred into transfer structure along the boundary, or directly transmitted to the other side of the boundary space. For the incident sound waves, in addition to the original space reflection reflection (scattering) acoustic energy, the remaining energy is considered to be the interface absorption edge. In a certain area of the acoustic energy is absorbed and the incident sound energy ratio is called the absorption coefficient of the boundary surface. Such as an indoor acoustic waves transmitted from an open window outside, the window area can be approximately one hundred percent believe that "absorb" the interior came the sound wave absorption coefficient is 1. Of course, we have to consider the sound-absorbing material, the main area of the opening does not depend on absorption, but also depend on the acoustic properties of the material itself, to absorb sound waves.

For two spaces in the middle of the interface compartment, when the incident sound waves from one room to the interface, sound wave vibration excitation barrier to the other side of the vibrating acoustic space radiation, which is transmitted sound waves。 Acoustic energy transmitted by the ratio of the incident wave energy of a certain area of said transmission coefficient。 For the open windows, the transmission coefficient can be approximated as 1 (sound absorption coefficient is 1), the insulation effect is zero, that is, the amount of noise is 0dB。 For heavy and thick brick wall or a steel plate, large mass per unit area, when the sound wave vibration can stimulate this tiny compartment, so that the acoustic energy to another space radiation (transmission sound energy) is very small, so the compartment sound large, good sound insulation。 But for the original space is concerned, most of the energy is reflected, so the absorption coefficient is small for a single material (not specifically designed for composite materials), the sound absorption and sound insulation effect is often not balanced。 As described above brick or steel can be used as good insulation material, but poor sound absorption; conversely, if you take good sound absorption performance materials (such as glass wool) insulation material to do, even when sound waves transmitted through the acoustic material can be absorbed 99% (which is difficult to achieve), only 1% of that sound can travel to another space, the sound transmission loss of this material is only 20dB, not a good insulation material。 The sound-absorbing material was mistakenly called "sound material" is wrong。 If someone describes some good acoustic absorption of a single material or, do not know it is that he is not in a lie。

  2. The sound-absorbing material

  Sound-absorbing material refers to a relatively large absorption coefficient of construction and decoration materials. If there are a lot of subtle interior material interconnected voids, voids formed by the passage of air can be simulated by the pipeline construction between solid framework for the formation of many thin tube or capillary composition. When sound waves pass, because the thin tube near the wall of the tube in the middle of acoustic vibrations at different speeds, the speed difference between the medium caused by internal friction, so that the acoustic vibration energy into thermal energy is absorbed. Good sound-absorbing material, mostly fibrous material, said porous sound-absorbing material, such as glass wool, rock wool, mineral slag cotton, linen and rayon, cotton, special metal fiber cotton, etc., as well as the gap in communication bubble plastic and the like. Absorption properties of the fiber structure of the material relating to the space, such as fiber thickness (microns to tens of microns as well) and material density, the volume of air within the material and the material volume ratio (known as the porosity, the porosity of glass wool in the 90 % or more), the shape of the void within the material structure. From the perspective of use, regardless of the mechanism of sound absorption can, as long as the inspection results to the material absorption coefficient. Of course, pay attention to material moisture, fire and a decorative and other requirements in the selection.

Porous sound-absorbing material has a fundamental absorption characteristics, namely low-frequency sound absorption is poor, high-frequency sound absorption is good. High frequency value to a certain neighborhood, in Figure 1, f0, absorption coefficient α reaches a maximum when the frequency continues to increase, some fluctuations in the high absorption coefficient. The location of f0, f0 is the wavelength corresponding to substantially four times the thickness t of the material.

When increasing the thickness of the material, it can improve the low-frequency sound absorption characteristics. When the same frequency absorption coefficient t2 is greater than the absorption coefficient t1. If t2 = 2t1, the same absorption coefficient corresponding to a frequency of about f2 = f1, ie double thickness increases frequency characteristics, low frequency sound absorption coefficient of a shift to low octave. It may have increased, but not to increase the thickness of the low-frequency sound absorption coefficient as the damping acoustic waves propagate in the void material, so increasing the thickness to improve the low-frequency sound absorption is limited. Different materials have different effective thickness. Like a kind of glass wool good sound-absorbing material, generally with a thickness of about 5cm, 10cm or more rarely used. And like a class than the micro-dense fiberboard material voids between the fibers of the material is very small, the damping of sound wave propagation is very large, only a small absorption coefficient, and the effective thickness is very small.

Poor low frequency sound absorption performance is generally plate-shaped sound-absorbing material is a universal law。 An improved method is to block sound-absorbing material is cut into a wedge shape, shown in Figure 2, when the acoustic wave propagates to the wedge-like material from the tip to the base, the ratio of air and material changes gradually, that sound impedance changes gradually, acoustic wave propagation beyond the limit on the effective thickness of plate-like material, to the base material, which can improve the low-frequency sound absorption performance。 Sound absorption frequency characteristics remain similar to Figure 1, the frequency f0 corresponding to the wavelength of maximum absorption coefficient of about 4 times the sound absorbing structure wedge length t。 For example, frequencies above 100Hz have a high absorption coefficient, sound absorption wedge length of about 87cm。 Of course, this sound absorbing structure generally should not be used for interior decoration, mainly used in the laboratory or special acoustic noise control engineering。

3. resonance absorption structure

Using different mechanism of resonance absorption, the design of various types of resonant absorption structure, so that the absorption peak at the desired frequency selected position, to meet the requirements of different frequencies of sound absorption, particularly to solve the problem of lack of low-frequency sound absorption.

The main advantage of the structure at several specialized clothing achieve sound absorption effect: resonance absorption thin porous sound-absorbing material, the film resonance absorption, resonance absorption sheet, perforated plate resonance absorption structure.

4. insulation materials

Airtight solid materials for acoustic airborne sound insulation has the effect, sound insulation effect is good or bad depends on the most fundamental thing is the quality of the material per unit area.

The barrier material has a certain elasticity in physics, when the sound wave will excite the vibration transmitted in the compartment. When sound waves are not perpendicular to the incident, but with the barrier at an angle θ incident, the sound wave reaches the front compartment followed by surface acoustic wave excitation and barrier first bending vibration wave propagation along the lateral compartment inside compartments, if bending wave when the propagation speed of sound in air gradually reaches the surface of the traveling speed barrier consistent sound wave vibration will strengthen bending waves, a phenomenon called coincident effect. Then bending wave vibration is particularly large degree of convergence, and to the other side of the air acoustic radiation energy is particularly large, thereby reducing noise effects.

5. The double insulation structure

According to the laws of mass, the frequency decreases by half, transmission loss to drop 6dB; and To improve sound insulation, mass doubling transmission loss increases 6dB. In this law under the control of, to significantly improve the sound insulation capacity, increase the quality compartment alone, for example, increasing the thickness of the wall, obviously it can not be effective, and sometimes even impossible, such as noise on an aircraft structure . The main way to solve this case is the use of double or even multi-layer insulation structure.

Double sound insulation structure model shown in Figure 8, mass per unit area, respectively m1, m2, a thickness of the intermediate air layer L. Transmission loss of two-layer structure can be carried out theoretical calculations, the result is more complex, in different frequency ranges can be simplified representation of different, here only for qualitative description.

Usually two double sound insulation structure, the same material without the same thickness, in order to avoid the emergence of the two layers fit the same frequency.

Pay special attention to the design and construction, you can not have a rigid connection between the two layers. Undermines the solid - air - solid two-layer structure, the solid barrier layers are connected by a rigid member, the vibration of the two compartments together, sound volume will be greatly reduced. Especially light double insulation structure must support each other or connected to each other, be sure to use an elastic member supported or suspended, while paying attention to the need to split between the two spaces, can not have seams or holes in communication. "Leak" will sound leakage, this is the actual problem of sound insulation.


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