Sound Absorbing Materials and Structures
Introduction
All building materials have specific sound absorption characteristics. Materials and structures with relatively large sound absorption coefficients (generally greater than 0.2) are called sound-absorbing materials or sound-absorbing structures in engineering.
The primary purposes of sound-absorbing materials and sound-absorbing structures are: to control reverberation time in sound quality design and to eliminate sound quality defects such as echo, and flutter echo. In noise control, it is used for indoor sound absorption and noise reduction, as well as pipe noise reduction in ventilation and air conditioning systems and exhaust pipes of power equipment.
The sound absorption coefficient is used to express the sound absorption capacity of the acoustic panel.
Types of Sound Absorbing Materials and Structures
The same material and structure have different sound absorption coefficients for sound waves of different frequencies. Generally, the sound absorption coefficients of six frequencies of 125, 250, 500, 1000, 2000, and 4000 Hz are used to represent the sound absorption frequency characteristics of materials and structures. Sometimes the arithmetic average of the sound absorption coefficients of the four frequencies of 250, 500, 1000, and 2000 Hz is also called the “noise reduction coefficient” (NRC). NRC is used to roughly compare and select acoustic panels in sound absorption and noise reduction.
The higher the sound absorption coefficients, the stronger the material’s ability to absorb sound waves. A material with a sound absorption coefficient of 1 completely absorbs all sound waves, while a material with a coefficient of 0 completely reflects sound waves. Therefore, when selecting sound-absorbing materials, the required sound absorption coefficients must be determined according to the needs of specific application scenarios.
There are many types of sound-absorbing materials and sound-absorbing structures, which can be divided into three categories according to their sound-absorbing mechanism, namely, porous sound-absorbing materials, resonance sound-absorbing structures, and composite sound-absorbing structures with both characteristics.
1. Porous sound-absorbing material
The structure of porous sound-absorbing materials, such as PET acoustic panels is characterized by a large number of internal and external connected voids and bubbles. When sound waves are incident on it, the air in the voids can be caused to vibrate. Due to the viscous resistance of the air and the friction between the air and the hole wall, a considerable part of the sound energy is converted into heat energy and lost. In addition, when the air is compressed adiabatically, heat exchange occurs continuously between the air and the hole wall, and part of the sound energy is also converted into heat energy due to heat conduction.
The sound absorption frequency characteristics of porous sound-absorbing materials are: the high-frequency coefficient is large, and the low-frequency sound absorption coefficient is small.
The factors affecting the sound absorption performance of porous sound-absorbing materials mainly include airflow resistance, porosity, apparent density, and structure factor of the material, among which the structure factor is a physical quantity determined by the structural characteristics of porous materials. In addition, factors such as material thickness, background conditions, surface conditions, and environmental conditions will also affect its sound absorption characteristics.
2. Resonance Sound Absorbing Structures
Resonance sound-absorbing structure is a material that eliminates or weakens sound waves through resonance effects. When the sound wave passes through the resonance sound-absorbing structure, the resonant structure inside the material will vibrate the sound wave, thereby converting it into heat energy and reducing the reflection and transmission of the sound wave. This process enables resonance sound-absorbing materials to effectively absorb sound waves of various frequencies, thereby mitigating noise pollution.
There are cavities with a certain thickness behind various perforated panels and slotted panels to form a resonance sound-absorbing structure. There are many factors that affect the acoustic performance of resonance sound-absorbing structures. In noise control projects, the perforation rate of resonance sound-absorbing structures is usually controlled at 1% to 5%. If the perforation rate is too large, there will be no resonance and sound absorption. In order to increase the sound absorption coefficient and effective sound absorption bandwidth, porous sound-absorbing materials can be placed in the cavity of the resonance sound-absorbing structure.
Acoustic Wood Slat Panels
CYATCO acoustic wood slat panels are porous sound-absorbing materials. Acoustic Wood Slat Panel is a beautifully crafted wood veneer slat panel, ideal for use on walls and ceilings. Suited for both commercial and domestic installations, the Acoustic Wood Slat Panel not only looks great, but it also offers superior ambient and reverberation noise control. The panels are also available in a number of other colors, meaning there’s a style and finish to suit any color scheme.
The advantages of CYATCO Acoustic Wood Slat Panels are their stability and versatility. They can be used in various environments for a long time and can be adapted to different application needs. CYATCO Acoustic Wood Slat Panels have good durability and anti-aging properties and can maintain good sound-absorbing effects over long-term use.
Summary
Sound-absorbing materials are used in a wide range of applications, including but not limited to offices, conference rooms, recording studios, theaters, and the interior of public transportation. The use of acoustic panels in these places can significantly reduce noise pollution, improve the acoustic environment of the space, and provide a more comfortable and pleasant working and living environment.