The world of soundproofing can seem confusing at times. What appears to be a simple task – to control the noise in a space – can quickly become an exercise in deciphering jargon, and getting confused about what exactly needs to happen. In this article, we’ll be looking at sound insulation, the process of reducing the amount of sound that travels between one space and another. We’ll unpicking two of the main methods involved in achieving sound insulation, and show how an ingenious application of simple physics can totally transform the acoustic comfort of a space.

What is Sound Insulation?

Put simply, sound insulation aims to reduce the amount of sound that is transferred between two or more spaces, through the placement of certain materials in areas where transfer can occur. In offices, hotels, gyms, and even homes it can be incredibly frustrating to hear noise coming from another room, and often this is a result of poorly planned materials or construction. Gaps in window frames, exposed pipes, flimsy walls and poorly designed floors are often culprits in creating environments where it can feel impossible to get any peace.


Sound Insulation: Method One

Sound insulation solves for this problem by applying materials to areas like these that act as a sound barrier. When a sound wave hits a solid surface, some of its energy is absorbed, some is transferred, and some of it is reflected. A process known as ‘deflection’ utilises the reflective properties of dense, solid materials, as in the case of concrete reinforcement, gap-sealant, plywood finishing boards or drywall. What’s known as the ‘mass law’ in physics suggests that, between certain thresholds, each time the mass of a given solid material doubles, its sound insulation capability increases by approximately 5dB. This is more effective for containing airborne sound such as voices or music, but less effective at containing ‘impact’ sounds like footsteps or the moving of furniture, as they usually have more concentrated, stronger levels of vibration.

Sound Insulation: Method Two

While adding materials to existing structures, or including them in the initial construction, can be effective at sound insulation, there is another trick that acoustics experts have up their sleeves for reducing the sound transfer between rooms: adding a buffer layer to floors, walls, ceilings or doors.

How Do Buffers Work?

Think about double-glazed windows for a moment. Think about how effective they are at keeping the noise of a busy road contained, as compared to single-glazed windows. Why is this? Having two layers of glass, with a layer of air between them, is an example of adding a buffer. Each time sound waves transfer between a non-rigid material, such as air or insulation, and a rigid material such as concrete or glass, their energy is greatly reduced. By creating a scenario in which sound waves must do this twice – from air to solid, air to solid and back into the air. In technical terms, this is sometimes called a mass-air-mass system, or a mass-spring-mass system.

Double-glazed glass (source:

These systems can be built in several ways. For walls, it is possible to float what one might call an ‘artificial’ wall on top of an original, structural wall, usually connected via steel studs. The gap between the floated wall and the original wall acts just like the air gap in a double-glazed window.  A similar process can be performed on floors, using joists to raise a secondary floor from the original one.

In many cases, mass-spring-mass systems are used in conjunction with sound insulating materials. For the non-rigid layers, glass wool, rock wool, polyester foam, or other natural materials and wools are often used, and for the rigid layer, wood, plasterboard and bricks are often used.

Example One

In the picture above we can see both lightweight sound absorbent materials working in tandem with a mass-spring-mass layout. The steel struts are there to support a structure in which a gap is placed between the original wall and a floated wall. Within the gap, there is some air, and sound-absorbent fibre insulation.

Example Two

In this case, ZENFEEL used light wood to support a structure in which coconut fiber acted as the sound insulating non-rigid layer. After this structure was completed, it was covered in acoustic panels.

Example Three

In this case, ZENFEEL replaced a moveable wall partition, that was not made of very sound-insulating materials and had small cracks between sections, with a layered partition wall. Once again, steel struts were used to support a structure with a non-rigid layer in the middle. The insulation effect was significant, raising the degree of insulation from 22db to 40db.

Example Four

In this case, the large white walls are in fact acoustic panels fitted by ZENFEEL. While thin, they absorb part of the sound, which contributes mainly to improving the reverberation within the room, but to a smaller extent also contributes to reducing the noise transferred to the other rooms. It was important in this project to maintain privacy and reduce noise for this office area.


Ultimately, the above methods of sound insulation work best in unison, and are only two possible ways in which sound between spaces can be controlled. Each room, each building, each space is different, and an expert review will always result in the best plan. It is always helpful, however, to know how and why certain methods are used in certain situations. By making use of the mass law, or creating mass-air-mass systems, sound insulation shows ingenuity and simplicity all at once. The next time you’re in a public space, an office or a store, look up and around, and you’ll notice how it is being put in place. Also feel free to reach out to ZENFEEL, for tailored information about how sound insulation could make your workplace a more comfortable place to be.