Sound-absorbing materials refer to materials whose average sound absorption coefficient for frequency is greater than 0.2. Most sound-absorbing materials are loose and porous materials, such as melamine foam, blankets, etc.
The role of sound-absorbing materials and sound-absorbing structures:
- Shorten and adjust the reverberation time;
- Control reflected sound
- Eliminate echo;
- Improve sound quality and change sound field distribution.
Since sound originates from the vibration of an object, it causes vibrations in the adjacent air to form sound waves, which propagate around in the air medium. As for sound-absorbing materials, when sound is transmitted to the surface of the component material, part of the sound energy is reflected, part penetrates the material, and part of it rubs against the surrounding medium due to the vibration of the component material or the sound propagating through it. This part is converted from sound energy into heat energy, and the sound energy is lost, that is, it is commonly said that sound is absorbed by the material.
Sound absorption coefficient:
The sound absorption performance of a material is expressed by the sound absorption coefficient α. A is the sum of the loss coefficient E absorption/E0 and the penetration coefficient E transmission/E0.
The sound absorption performance of the material is not only related to the structure, thickness and surface characteristics of the material itself, but also related to the incident direction and frequency of the sound.
Sound-absorbing materials are usually used to control indoor volume and sound quality. Generally, the larger the room volume, the longer the reverberation time, and the worse the speech intelligibility. In order to ensure speech intelligibility, it is necessary to absorb sound in the room and control the reverberation time. Such as auditoriums, classrooms, stadiums, and cinemas.
The requirements for sound-absorbing materials used in music buildings will be stricter. The use of sound-absorbing materials should ensure a certain fullness of the sound and appropriately extend the reverberation time. In order to prevent acoustic defects such as echo, acoustic feedback, and sound focusing, sound-absorbing materials can be used on the rear wall, second-floor terrace railings, side walls, and other parts.
The sound-absorbing materials used in the design of the building’s acoustic environment also need to comprehensively consider the use of materials, including sound absorption performance and decorative properties, strength, fire protection, moisture absorption, processing and other aspects.
Structural types of sound-absorbing materials
There are many types of sound-absorbing materials and structures. According to their different material structures, they can be divided into the following categories:
(1) Porous sound-absorbing materials: fibrous sound-absorbing materials, granular sound-absorbing materials and foam sound-absorbing materials;
(2) Resonant sound-absorbing structure: single resonator, perforated plate resonant sound-absorbing structure, thin plate resonant sound-absorbing structure;
- Special sound-absorbing structure: thin film resonance sound-absorbing structure.
Resistive attenuation type
Resistive attenuation soft porous materials are commonly known as melamine foam and glass wool. Hard porous materials include metal, ceramic, and synthetic resin porous materials, among which aluminum sound-absorbing materials have attracted people’s attention. The reason is that metal porous materials are rigid bodies and do not need to be protected by perforated surface materials like soft porous materials. They will not age or scatter to pollute the environment after long-term use. The sound absorption coefficient after moisture absorption or moisture will basically not affect its sound absorption performance.
Thin film vibration type
Thin film vibration sound-absorbing materials are usually attached to other materials, such as aluminum foil in aluminum fiber sound-absorbing materials. There is also microperforated polyethylene film, which can be attached to the glass of ordinary windows. Sound absorption performance: It has excellent mid-frequency sound absorption characteristics.
Space sound absorber
The difference between space sound absorbers and general sound absorbing structures is that they are not combined with rigid walls such as ceilings and walls to form a sound absorbing structure, but are self-contained systems. Indoor sound absorption treatment generally involves installing sound-absorbing materials on various indoor interfaces during building construction and decoration. However, sound-absorbing components: space sound absorbers can be prefabricated and hoisted on site. In essence, the sound absorber is not a new sound-absorbing structure, but due to different usage conditions, the sound absorption characteristics are also different. Hanging it in a location with high sound energy flow density (such as near the sound source or where the reflection is focused) can achieve better results.
Strong sound absorber
Sound-absorbing wedges are commonly used strong sound-absorbing structures in anechoic chambers, as well as interface tiled porous materials.
The curtain is at a certain distance from the wall and window glass, as if there is an air layer behind the porous material. Although it is not completely closed, it still has a certain sound absorption effect on medium and high frequencies.
Entrance of cave
An opening open to the free outdoor sound field is completely sound-absorbing from an indoor perspective, with a sound absorption coefficient of 1 for all frequencies. It has a greater impact on room acoustics issues. If the hole is not facing the free sound field, its sound absorption coefficient will be less than 1.
People and furniture
People and furniture can also absorb sound, so they are sound absorbers. The absorption volume of general sound-absorbing materials and structures can be calculated based on the product of their sound absorption coefficient and effective area. Therefore, the sound absorption characteristics are expressed by the absorption volume of each person or each piece of furniture. The product of them and the number (or number of pieces) is the total absorption volume.
With the rapid development of modern science and technology, there will be more and more types and functions of acoustic materials. In order to meet people’s growing demand for sound-absorbing materials, the application of sound-absorbing materials will become more and more extensive in the future.
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