Have you ever wondered why EVA foam is used for soundproofing, why acoustic foam absorbs sound well, or why glasswool can both insulate and absorb sound? The answer lies in the different molecular structures and compositions of these materials.
Is Soundproofing the Same as Sound Absorption?
Soundproofing and sound absorption are two acoustic concepts with entirely different properties. However, many people still confuse these terms, leading to ineffective sound treatment and unsatisfactory acoustic quality.
What Is Soundproofing?
Simply put, soundproofing is the process of blocking sound, preventing it from traveling from one space to another—either from inside to outside or vice versa. To effectively block the transmission of sound waves, dense materials with a closed molecular structure such as concrete, glass, stone, and bricks are required.
What Is Sound Absorption?
Sound absorption involves using soft, porous materials that allow sound waves to enter but prevent them from reflecting off hard, smooth surfaces like walls, ceilings, and floors, which cause echoes and reverberation. By reducing reflected sound, acoustic absorption enhances clarity and sound quality.
Whether a material is soundproof or sound-absorbing depends on its composition and molecular structure.
Structure of Some Commonly Used Soundproofing and Acoustic Absorption Materials
1. PE Foam
PE foam, short for Polyethylene, is also known as PE foam sheet, white foam, structured foam, or acoustic foam.
PE foam consists of layers of polyethylene infused with air bubbles, creating a closed molecular structure with millions of tiny interconnected air pockets. This structure effectively prevents sound transmission.
Laboratory tests conducted at DASM Institute have shown that PE foam performs better at low frequencies, with a maximum soundproofing capability of up to 42dB.
Applications: PE foam is widely used as a soundproofing and noise-reducing layer in ceilings, walls, and floors for buildings such as apartments, train stations, schools, hospitals, theaters, recording studios, and bars.
2. XPS Foam
Extruded Polystyrene (XPS) foam, also known as pink foam, lightweight insulation foam, or underlayment foam, is produced through a continuous heating and extrusion process. This process results in a closed-cell structure with a smooth outer surface, enhancing its ability to block sound transmission. XPS foam is among the top soundproofing materials, capable of reducing noise by up to 60dB at low frequencies.
Applications: XPS foam is used in walls, ceilings, floors, and roofs of residential, commercial, and industrial buildings, including factories, warehouses, and shopping centers.
3. Acoustic Pyramid Foam
Acoustic pyramid foam is one of several popular foam designs, including pyramid, egg-crate, corner, and wedge-shaped foam.
Microscopic examination reveals that this foam has fine, porous cells arranged in a honeycomb-like structure with open interconnected molecules. These air pockets vibrate and convert sound energy into heat, preventing sound waves from bouncing back off hard surfaces like walls, floors, and ceilings. This foam is particularly effective at absorbing mid-to-high frequency sounds.
Applications: Used as a surface acoustic treatment for recording studios, livestream rooms, music rooms, home theaters, machine rooms, and more.
4. EVA Foam (Synthetic Rubber)
EVA foam, also known as EVA rubber, is a widely used soundproofing and vibration-damping material.
It is a semi-rigid material with a chemically cross-linked molecular structure. Under a microscope, EVA foam exhibits a closed molecular structure, making it an excellent sound-blocking material.
Laboratory tests indicate that EVA foam can provide up to 65dB of sound insulation, along with excellent shock absorption and vibration damping properties.
Applications: EVA foam is commonly used as an inner soundproofing layer within walls or as an underlayment to reduce vibrations and noise.
5. Sonic Acoustic Panels
Sonic acoustic panels, made from compressed polyester fibers, are among the top sound-absorbing materials available today. With a Noise Reduction Coefficient (NRC) close to 1, they can absorb up to 94% of sound waves impacting walls, ceilings, and floors.
Microscopic images show a dense yet porous non-woven fiber structure, with air gaps that allow sound energy to be absorbed.
Applications: Sonic acoustic panels are used for ceiling-mounted acoustic tiles, wall-mounted acoustic panels, decorative acoustic artwork, pin-boards, sound-absorbing curtains, and more. They are found in home theaters, recording studios, offices, schools, libraries, and restaurants.
6. Straw-Based Acoustic Panels
Straw is a 100% natural and eco-friendly material with a hollow fiber structure that makes it highly effective at sound absorption. Testing has shown that straw-based acoustic panels have an NRC close to 1, comparable to mineral wool and Sonic acoustic panels.
Additionally, DASM Institute researchers have discovered that when straw fibers are combined with materials like cement, they also gain excellent sound-blocking properties. A 45mm thick straw panel provides soundproofing equivalent to a 100mm thick concrete wall, making it highly effective at blocking sound in the 1,000–2,000Hz frequency range.
7. Fiberglass Wool (Glass Wool)
Glasswool is made from fine synthetic glass fibers, similar to wool. Under a microscope, this material exhibits a fiber-based structure with numerous tiny air pockets, increasing its ability to absorb and block sound.
Glasswool is recognized for both soundproofing and sound absorption, with an NRC of 0.85 and a soundproofing capability of up to 35dB.
Applications: Fiberglass wool is often used as an internal acoustic and soundproofing layer within walls, placed between other materials with an air gap to maximize absorption and prevent sound reflection.
8. Acoustic Fabric
Acoustic fabric, also known as sound-absorbing fabric or felt fabric, consists of densely compressed fibers with air pockets that enhance sound absorption.
Laboratory tests show that acoustic fabric can absorb about 30% of sound, particularly in the mid-to-high frequency range, improving audio clarity and reducing echo.
Applications: Acoustic fabric is used as a lining behind perforated acoustic wood panels, covering insulation materials like rock wool, fiberglass, and metal ceiling panels, and reducing noise in HVAC ducts.
Through this article, you now understand the key differences between soundproofing and sound absorption, as well as the most commonly used materials for acoustic treatment.
At DASM Institute, we specialize in the research and development of acoustic materials. We not only analyze and diagnose acoustic problems but also design effective sound treatment solutions tailored to your needs, helping you achieve optimal sound performance while minimizing costs.
For expert acoustic consultation and solutions, contact DASM Institute today!
