If your house has poor sound insulation, is it really effective to buy soundproofing cotton/egg cotton and cover the walls with it?

A few days ago, a friend of mine rented an apartment in a Hangzhou community at a high price. As soon as she moved in, she discovered a major soundproofing problem. Her neighbor liked to listen to audiobooks on a stereo. Although it wasn't too late or too early, for some people who sleep in, Saturday mornings are very important. Being forced to wake up at eight o'clock to listen to audiobooks instantly dampened their spirits.

Poor sound insulation is what everyone is doing:

My friend had no knowledge of soundproofing, and the first method she found was to cover the non-soundproof wall with sound-absorbing cotton like eggshell cotton. She wasn't alone in this thinking; many people without soundproofing knowledge held the same idea.

1. Despite the noise from my floor disturbing the downstairs neighbors, I bought soundproofing cotton (it's unclear whether it's actually soundproof, but it looks like it) and stuck it on the door – what a bizarre thing to do.

2. The idea of ​​buying soundproofing cotton to cover the windows and glass doors in the house because they are not well soundproofed.

Then I realized that for many people who lack knowledge about soundproofing, buying lightweight, self-adhesive, inexpensive, and seemingly soft cotton materials like soundproofing cotton is a subconscious soundproofing measure. (The softness and warmth of cotton visually create a sense of security and quiet.)

So, is it actually effective to use soundproofing cotton to increase the sound insulation of walls or doors and block external noise? Today, we'll explore the principles behind soundproofing cotton and whether it's truly useful for houses with poor sound insulation.

The working principle of sound insulation cotton:

Sound is produced when an object vibrates. Sound waves travel through the air. Cotton has a multi-fiber structure. When sound waves pass through cotton, they are reflected, superimposed, and collided by countless fibers. The sound wave energy is converted into heat energy, the sound wave intensity weakens, and the sound disappears.

The sound insulation function of sound-absorbing cotton is related to the material's fiber structure and the open space within it, such as the fiber fineness (ideally between micrometers and tens of micrometers), material density, the ratio of air volume to material volume (called the open space ratio, with glass wool having an open space ratio of over 90%), and the shape and structure of the open spaces within the material. The ratio of absorbed sound energy to incident sound energy over a given area is called the sound absorption coefficient of that boundary surface. Materials with a ratio greater than 0.3 are called sound-absorbing cotton.

Is applying soundproofing material alone effective?

It works, but the sound insulation is very poor.

We need to distinguish between a key data point: sound absorption coefficient and sound insulation. Cotton essentially absorbs sound, while sound insulation boards/felts provide sound insulation.

Sound-absorbing materials reflect very little incident sound energy, meaning sound energy easily enters and passes through them. Sound-insulating materials, on the other hand, must reduce transmitted sound energy and block sound propagation; they cannot be as porous, loose, and permeable as sound-absorbing materials. Sound insulation uses heavy and dense materials such as steel plates, lead plates, and brick walls. Therefore, sound absorption and sound insulation are two completely different acoustic concepts. Sound-insulating materials are dense and high-density, while sound-absorbing materials are loose and low-density. The primary performance characteristic of sound-insulating materials is sound insulation, with a low sound absorption coefficient; the primary performance characteristic of sound-absorbing materials is sound absorption, with little sound insulation.

Sound absorption and sound insulation are fundamentally different, but in practical engineering applications, they are often combined to achieve a comprehensive noise reduction effect. For example, to avoid interference from higher-level noise in adjacent rooms, a sound insulation system is typically formed by combining sound insulation cotton with sound insulation boards/felt. This is a composite sound insulation solution that reduces repeated sound reflections between the two boards, improving the sound insulation of the composite wall as a whole structure. Soundproof enclosures are often a combination of sound insulation and sound absorption materials. They typically use metal plates with sound-absorbing materials laid inside, greatly increasing the actual sound insulation of the enclosure to near that of the metal plates. In short, the rational combination of sound-absorbing and sound-insulating materials leverages the respective advantages of each material's properties, thereby improving the sound insulation and noise reduction effect.

What is the final effect of using sound insulation cotton alone?

For example, my friend's method involved buying soundproofing cotton separately and sticking it to the wall. What would be the final effect?

By applying sound-absorbing cotton separately, sound reflections can be reduced, lowering indoor reverberation and noise. This is commonly used in home theaters, recording studios, dubbing rooms, karaoke rooms, and music rooms-places where audio enjoyment is desired. However, when purchasing these products, the product descriptions themselves state: sound absorption and noise reduction, improved sound quality. They don't actually offer significant soundproofing.

How to easily soundproof a house with poor sound insulation?

If your house has poor sound insulation, you can't just buy soundproofing cotton; you need to redo the renovation and use a composite solution of soundproofing cotton and soundproofing panels to solve the problem. Therefore, for renters, if your roommates or neighbors are noisy, simply buying soundproofing cotton won't be very effective.

Many people are unwilling to invest too much effort in basic soundproofing, so they prefer to simply endure the noise. In this situation, our suggestion is to use a compromise solution that offers some soundproofing capability and is relatively convenient:

Soundproof curtains

The biggest advantage of soundproof curtains is that they are easy to install without damaging the building structure, while ensuring a certain level of sound insulation (at least 15-20 decibels). If renting, they can also be removed and taken away for continued use. Whether soundproof curtains actually provide sound insulation depends on their design, not simply on increasing their thickness. It's important to check for actual measurement data, videos verifying their effectiveness, and environmental standards.

If you would like to learn more about " soundproof curtains ", please feel free to contact me.