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Sound-absorbing material and soundproof material difference

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Sound-absorbing material and soundproof material difference

Release date: 2016-11-30 Author: Click:

Interior decoration has become an independent industry, large and small decoration companies like springing up everywhere. Many decoration companies to new styles, new materials, new technology to the interior decoration brought a new look, reaching a new level. In this case,
The interior acoustics design is a systemic subject, involving a wide range, this article only on the interior and sound-absorbing and sound insulation of the material and structural knowledge for a brief introduction, decorative works and the owners of the acoustic materials and structures Understanding, to understand why the acoustic design for such and such processing, so that decorative works in the aesthetic and acoustic requirements to achieve perfect unity.

1. The basic concepts of sound absorption and sound insulation

First of all, to clear sound and sound insulation is completely different from the two acoustic concepts. Sound absorption refers to the sound wave can be reflected (or scattered) by the boundary surface when the acoustic wave propagates to a boundary surface, and part of the sound energy can be absorbed by the boundary surface (this is not considered to be absorbed by the medium when propagating in the medium). Boundary material into heat energy is consumed or converted into vibration energy transfer structure along the boundary transfer, or directly transmitted to the other side of the border space. For the incident sound waves, in addition to reflecting the original space reflection (scattering) sound energy, the rest of the energy is considered to be absorbed by the boundary surface. In a certain area to be absorbed on the sound energy and incident sound energy ratio is called the boundary surface of the sound absorption coefficient. For example, indoor sound waves from the open window to the outside, then the window area can be considered almost 100% "absorption" of the sound coming from the room, a sound absorption coefficient of 1. Of course, we have to consider the sound-absorbing material, mainly by the open area of the sound absorption, and rely on the acoustic properties of the material itself to absorb sound waves.
When the sound waves enter the interface from one chamber, the acoustic wave excites the vibrations of the interlayer, and transmits the acoustic wave to the other side of the space, which is the transmitted sound wave. Through a certain area of the transmission of sound energy and the sound wave energy ratio of transmission coefficient. For open windows, the transmission coefficient can be approximately 1 (sound absorption coefficient is 1), the sound insulation effect is 0, that is, the sound insulation is 0dB. For heavy and heavy brick walls or thick steel plate, the quality of the unit area is large, the sound waves can only stimulate the small vibration of this compartment, so that the radiation energy of another space (transmission sound energy) is very small, Sound volume, good sound insulation. But for the original space, the vast majority of energy is reflected, so the sound absorption coefficient is very small for a single material (not specifically designed composite material), air-laid machine sound absorption and sound insulation is often not take into account . Such as the above-mentioned brick or steel plate can be used as a good sound insulation material, but the poor sound absorption; in turn, if the sound absorption performance of good materials (such as glass wool) do sound insulation material, even if the sound waves through the material sound Can be absorbed 99% (which is difficult to achieve), and only 1% of the sound energy to another space, this material is only 20dB sound insulation, not a good sound insulation material. Some people mistakenly believe that sound-absorbing material as "noise material" is wrong. If someone introduces a sound absorption of a single material good sound Ye Hao, that he did not understand is a lie.

  2. Sound-absorbing material

Sound-absorbing material is relatively large sound absorption coefficient of building decoration materials. If there are many fine interstices in the material, the air passages formed by the voids can be modeled as a pipe structure consisting of many thin tubes or capillaries between the solid frames. When the acoustic waves, due to the tube near the tube wall and tube in the middle of the acoustic vibration velocity is different from the inter-media speed difference caused by internal friction, so that the vibration energy into heat energy is absorbed. Good sound-absorbing materials are mostly fibrous materials, said porous sound-absorbing materials, such as glass wool, rock wool, mineral wool cotton, cotton and man-made fiber cotton, special metal fiber cotton, etc., also includes the gap connected foam Plastic and the like. The sound absorption performance is related to the fiber void structure of the material, such as fiber thickness (micron to tens of microns is good) and material density, material air volume and material volume ratio (called porosity, glass wool porosity of 90 % Or more), and the shape and structure of voids in the material. From the use of the point of view, regardless of the mechanism of sound absorption, as long as access to material absorption coefficient of the experimental results can be. Of course, in the selection of materials should also pay attention to moisture, fire and can be decorative and other requirements.
Porous sound-absorbing material has a basic sound-absorbing properties, namely, poor low-frequency sound absorption, high-frequency sound absorption is good. Frequency high to a certain value in the vicinity, see Figure 1 f0, the sound absorption coefficient α to the maximum, the frequency continues to increase, the absorption coefficient in the high-end some fluctuations. The location of this f0, in general, f0 corresponds to the wavelength of the material thickness t 4 times.
When the material thickness is increased, the low frequency sound absorption characteristics can be improved. At the same frequency, the sound absorption coefficient of t2 is greater than the absorption coefficient of t1. If t2 = 2t1, then the same sound absorption coefficient corresponding to the frequency of about f2 = f1, that is, double the thickness, low-frequency sound absorption coefficient frequency characteristics to low frequency one octave. However, it is not always possible to increase the thickness by increasing the low frequency sound absorption coefficient because the sound waves are damped as they propagate through the voids of the material, increasing the thickness to improve low frequency sound absorption. Different materials have different effective thicknesses. Like a good class of glass wool sound-absorbing material, generally about the thickness of 5cm, rarely used more than 10cm. And like fiberboard a kind of more dense material, the material fiber gap is very small, the sound wave transmission damping is very big, not only the sound absorption coefficient is small, and the effective thickness is also very small.
Generally flat sound absorption properties of low-frequency sound absorption is a general rule. An improved method is to cut the monolithic sound-absorbing material into a wedge shape, as shown in Fig. 2. As the acoustic wave propagates to the cleft material, the ratio of air to material gradually changes from tip to base, Impedance gradually changes, the sound wave propagation beyond the effective thickness of the plate-like material to the base of the material, which can improve the low-frequency sound absorption performance. The sound absorption frequency characteristic is still similar to that of Fig. 1, and the frequency f0 of the maximum sound absorption coefficient corresponds to a wavelength approximately four times the length t of the cleaved sound absorption structure. For example, to make the frequency above 100Hz have a high absorption coefficient, the length of the sound-absorbing wedge about 87cm or so. Of course, such a sound-absorbing structure is generally not suitable for interior decoration, mainly for acoustic laboratory or special noise control engineering.

3. Resonance sound-absorbing structure

Using different resonance absorption mechanism, design various types of resonant sound absorption structure, so that the absorption peak selection in the desired frequency position to meet the requirements of different frequencies of sound absorption, in particular, to solve the problem of low-frequency sound absorption.
The main use of several professional structure to achieve the effect of sound absorption: thin layer of porous sound-absorbing material resonance absorption, film resonance absorption, sheet resonance absorption, perforated plate resonant sound-absorbing structure.

4. Sound insulation material
Airtight solid material, the airborne sound waves have sound effects, sound insulation effect of the most fundamental point is depends on the quality of the material per unit area.
The spacer material has a certain flexibility in physics, when the sound waves when the vibration will stimulate the spread in the compartment. When the sound waves are not perpendicular to the incident, but with the barrier at an angle of θ incident, the acoustic wave front to reach the barrier surface, and the first layer of acoustic excitation barrier vibration waves along the lateral spread, if the bending wave The propagation speed and the sound waves in the air gradually reach the surface of the travel speed of the same layer, the sound waves will strengthen the bending wave vibration, a phenomenon known as the anastomosis effect. Bending wave vibration at this time the extent of particularly large, and to the other side of the air radiation in the energy of sound waves are particularly large, thereby reducing the noise effect.

5. Double-layer sound insulation structure

According to the law of quality, the frequency is reduced by half, the transmission loss to drop 6dB; and to improve the sound insulation effect, the quality doubled, transmission loss increased 6dB. Under this law, if the sound insulation capacity is to be significantly increased, it is obviously not feasible and sometimes impossible, for example, to increase the wall thickness by increasing the quality of the partition, such as the sound insulation structure on aircraft . The solution is mainly to use double or even multi-layer sound insulation structure.
Double insulation structure model shown in Figure 8, the mass per unit area is m1, m2, the middle air layer thickness L. The transmission loss of the double-layer structure can be calculated theoretically. The results are complex and can be expressed in different frequency ranges. Here, only the qualitative description is given.
Generally two-story sound insulation structure of the two layers, without the same thickness of the same material, in order to avoid these two layers appear the same frequency of anastomosis.
In the design and construction should pay special attention to the two layers can not have a rigid connection. The solid-air-solid double-layer structure is destroyed, and the two solid layers are connected by rigid members, so that the vibrations of the two partitions are connected together, and the sound insulation quantity is greatly reduced. In particular, double-layer light structure sound insulation, must be mutually support each other or connected, be sure to use elastic support or suspension, while attention needs to be split between the two space, not seam or hole connected. "Leakage" will leak sound, this is the actual problem of sound insulation.

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