A Guide to the Principles and Practical Applications of Acoustic Materials

Noise is ubiquitous, impacting not only our quality of life but also potentially harming our health. To create a quiet and comfortable environment, acoustic materials have emerged. These materials, with their different working principles and properties, offer diverse options for solving noise problems. Next, we will delve into the working principles of acoustic materials, including sound absorption, sound insulation, and damping vibration reduction, analyze the performance of mainstream acoustic materials, and provide practical soundproofing solution recommendations based on real-world case studies.

I. Principles of Acoustic Materials

(I) Sound Absorption Principle: Sound is essentially a mechanical wave that interacts with objects during propagation. The working principle of sound-absorbing materials is based on porous or resonant structures. When sound waves enter a porous sound-absorbing material, such as polyester fiber sound-absorbing cotton, the sound waves are continuously reflected and refracted within the material's pores, interacting with air molecules and the material's solid framework through friction and adhesion. This friction and adhesion converts sound energy into heat energy, thus consuming the sound energy and achieving sound reduction. Resonant sound-absorbing structures, such as perforated plate resonant sound-absorbing structures, utilize the matching of sound wave frequency with the inherent frequency of the resonant structure to induce resonance. This causes sound energy to be converted into heat energy and dissipated during resonance, achieving a sound absorption effect.

(II) Sound Insulation Principle: Sound insulation materials primarily rely on their density and mass to block sound transmission. When sound waves encounter a sound insulation material, some sound is reflected back at the material's surface, while some attempts to propagate through the material. According to the law of mass, the thicker and denser the material, the better its sound insulation performance. For example, metal materials such as steel plates, due to their high density and compact structure, can effectively reflect and block sound waves, reducing sound transmission. Furthermore, the combination of multiple layers of different materials, through the air layers or damping materials between the layers, can further improve the sound insulation effect, because different materials have different characteristics in reflecting, absorbing, and transmitting sound waves, and their combination can more comprehensively weaken sound waves.

(III) Damping and Vibration Reduction Principle: When an object vibrates, it generates structural noise that propagates through the solid. Damping and vibration reduction materials increase the internal losses of the structure, converting vibrational energy into heat energy and dissipating it, thereby suppressing the object's vibration. Common damping materials include viscoelastic damping materials. When a structure vibrates, the molecules inside the damping material undergo relative motion. The friction and internal loss between molecules consume the vibrational energy, reducing the amplitude of the structure's vibration and thus reducing the noise generated by the vibration. For example, attaching damping material to the casing of mechanical equipment can effectively reduce the vibration noise during equipment operation.

II. In-depth analysis of mainstream acoustic materials

(a) Polyester fiber sound-absorbing cotton

1. Performance: Polyester fiber sound-absorbing cotton is a porous sound-absorbing material made of 100% polyester fiber through hot pressing. It possesses excellent sound absorption performance, with a significant absorption effect on mid-to-high frequency sounds, exhibiting a high sound absorption coefficient in the 200-2000Hz frequency range. Furthermore, the material is environmentally friendly and non-toxic, achieving a fire rating of B1, and does not release harmful gases, posing no harm to human health. In addition, polyester fiber sound-absorbing cotton is soft in texture, possessing good flexibility and impact resistance, and is not easily damaged.

2. Process: Made from polyester fiber raw materials through carding, web laying, and hot pressing. No glue is added during production; the material is formed relying on the inherent thermal bonding properties of the fiber, ensuring its environmental friendliness.

3. Advantages and disadvantages: Advantages include good sound absorption performance, strong environmental friendliness, and easy installation; it can be directly cut and laid or pasted on walls, ceilings, etc.; various colors are available to meet the needs of different decoration styles. Disadvantages include poor waterproof performance; its sound absorption performance will decrease when exposed to a humid environment for a long time, and its absorption effect on low-frequency sounds is relatively weak.

4. Applicable scenarios: Widely used in home theaters, recording studios, KTVs and other places with high requirements for sound quality, to absorb excess reflected sound and improve the indoor acoustic environment; also suitable for offices, conference rooms and other spaces to reduce environmental noise and improve office efficiency.

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(ii) Rock wool

1. Performance: Rock wool is a man-made inorganic fiber made primarily from natural rocks such as basalt and dolomite, melted at high temperatures. It possesses excellent sound absorption and heat insulation properties, exhibiting good absorption of mid-to-low frequency sound, performing exceptionally well in the 31.5-500Hz frequency range. Furthermore, rock wool has a Class A fire rating, classifying it as a non-combustible material with excellent fire resistance; it also boasts good chemical stability, resisting corrosion from acids, alkalis, and other chemicals, resulting in a long service life.

2. Process: Natural rocks are crushed and melted at a high temperature of 1450-1500℃. They are then processed into fibers through high-speed centrifugation or blowing, and then processed into rock wool products of different specifications through processes such as collection, curing, and cutting.

3. Advantages and disadvantages: Advantages include excellent sound absorption, heat insulation, and fire resistance; relatively low price; and high cost-effectiveness. Products can be manufactured in different densities and thicknesses to suit various application scenarios. Disadvantages include a relatively hard texture that can be sharp and prickly during installation, requiring careful protection of workers; the fibers may irritate the respiratory tract and skin, necessitating protective measures; and the high hygroscopicity of rock wool can affect its performance when damp.

4. Applicable scenarios: Commonly used for building exterior wall insulation and soundproofing, industrial equipment sound and heat insulation, computer rooms and other places with high requirements for fire prevention and sound insulation.

(iii) Sound insulation felt

1. Performance: Sound insulation felt is a flexible sound insulation material composed of polymer materials and other auxiliary materials. It has a high density and excellent sound insulation performance, with a significant effect on blocking low-frequency sounds. At the same time, sound insulation felt is flexible and can be cut and bent arbitrarily, making it easy to install on various complex structural surfaces; it also has strong weather resistance, maintaining stable performance under different temperature and humidity environments.

2. Process: It is made by mixing high molecular polymers with metal powders, rubber and other materials, and by calendering and other processes, so that it has high density and good flexibility.

3. Advantages and disadvantages: The advantages are outstanding sound insulation performance, especially against low-frequency noise; flexible and easy installation, and it can be used in conjunction with other materials, such as combining with gypsum board to form a soundproof wall. The disadvantages are that the material itself does not have sound absorption function, and the sound insulation effect is limited when used alone; the appearance is poor, and surface decoration treatment is generally required.

   Applicable scenarios: Suitable for soundproofing of home doors and windows, pipes, KTV rooms, etc., effectively blocking external noise from entering the room; it can also be used for soundproofing and noise reduction in industrial plants to reduce the impact of equipment operating noise on the surrounding environment.

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III. Suggestions for Soundproofing Solutions in Practical Case Studies

(a) Home Theater Soundproofing Solution

A home theater requires a good acoustic environment to ensure an immersive experience for watching movies and listening to music, while avoiding disturbing neighbors.

1. Wall treatment: First, lay a layer of polyester fiber sound-absorbing cotton on the wall, with a thickness of 5-8cm, to absorb mid-to-high frequency sounds, reduce indoor reflected sound, and improve sound clarity. Then, install sound insulation felt on the outside of the sound-absorbing cotton and fix the sound insulation felt to the wall frame to form a sound barrier, blocking sound from propagating outwards. Finally, install plasterboard for surface decoration. The air layer formed between the plasterboard and the sound insulation felt further improves the sound insulation effect.

2. Ground treatment: Lay sound-absorbing and vibration-damping pads on the ground to reduce the transmission of vibrations generated during equipment operation through the ground. Then lay wooden flooring or tiles on the vibration-damping pads for decoration and protection.

3. Door and window treatment: Choose soundproof doors and windows with good sealing performance. Windows can be double-glazed with inert gas filling the space between them to improve sound insulation performance. For doors, choose solid wood composite doors filled with sound insulation materials and install sealing strips to ensure that there are no gaps when the doors and windows are closed.

(II) Sound Insulation Solution for Industrial Plants

Industrial plants contain numerous pieces of equipment and generate significant noise, necessitating a comprehensive approach that considers sound absorption, sound insulation, and damping vibration reduction.

1. Equipment sound insulation: For large mechanical equipment, damping material is attached to the equipment shell to reduce noise generated by equipment vibration. Then, a soundproof cover is installed around the equipment. The inner layer of the soundproof cover uses polyester fiber sound-absorbing cotton to absorb sound, and the outer layer uses steel plate or sound insulation board to insulate sound, reducing the outward diffusion of equipment noise.

2. Wall and roof treatment: Rock wool boards are laid on the walls and roof, with the thickness selected according to actual needs, generally 10-15cm, to absorb and block noise in the factory. At the same time, perforated resonant sound-absorbing structures are installed on the walls and roof to further improve the absorption effect of mid- and low-frequency sounds.

3. Ventilation and ductwork treatment: Install silencers at ventilation openings. These silencers utilize resistive noise reduction principles and are filled with sound-absorbing material to reduce noise generated by airflow. For ductwork, wrap it with sound-absorbing felt to reduce the propagation of noise generated by fluid flow within the ductwork.

By gaining a deep understanding of the working principles of acoustic materials and a comprehensive grasp of the characteristics of mainstream acoustic materials, and by combining different acoustic materials in a reasonable manner according to actual scenarios, we can develop efficient sound insulation solutions to effectively solve various noise problems and create a quiet and comfortable living and working environment for people.