What is Acoustic Decoupling and How Does It Work?

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When living in an apartment or a room with shared walls, you’re surrounded by noise from outside your room and from the room itself. On one shared wall, you have a neighbor playing loud bass music.

On the next, you have a kid practicing for his upcoming music band festival and on the other is a couple quarreling or kids playing.

If you ever find yourself in such mayhem, creating a room through acoustic decoupling can help permanently ease the noise problem. Below is a guide on how acoustic decoupling work in detail.

What is Acoustic Decoupling?

In general, decoupling means separating solid objects. Acoustic decoupling simply means separating two things to sound attenuation between the structure. Decoupling is one of the four basic elements of soundproofing.

Sound is nothing but a vibration. The vibration will travel through conduction easily if there’s a solid direct pathway to follow.

Here’s an example, think of how as kids, you’d connect two orange juice cans with a piece of string. You’d talk on one end of the can, and your friend would perceive the information on the other end.

Now, if we cut the string “decouple the juice cans” on the sound pathway, the sound vibrations would stop since there’s no conduction.

We want less sound to travel through the walls, ceilings, and floors in soundproofing. Decoupling the framing in our ceilings and wall would result in enormous sound attenuation. Acoustic decoupling is an affordable and highly effective soundproofing method.

Acoustic Decoupling a Wall?

There are three methods to effectively decouple a wall. The most effective is creating a double stud wall with a green glue compound.

Double Stud Wall: as its name suggests, a double stud wall is made up of two stud-framed walls installed next to each other to create a thick wall cavity which makes it almost impossible for vibration noise to pass between the walls.

With a double stud wall, you’re able to build what’s commonly known as Room Within a Room (RWAR). This helps isolate sound and prevent transmission to the inside or outside the room.

Staggered Stud Wall: this is similar to the double stud framed walls but slightly different. The space between the studs is smaller, making it less effective than double-stud walls.

You can use a wider sill plate with the studs installed in a staggered alignment. The studs are rotated from the two walls to ensure that no stud touches either side of the walls.

The top and base plates of the staggered stud wall should be 2by6 inch boards instead of the standard 2by4 inches boards.

Resilient Clips and Hat Channels: if the room you need to soundproof is smaller, then using resilient clips and hat channels is the way to go. The problem with double and staggered walls is that they take up too much valuable space and are complex to construct.

The resilient channels and clips can be attached to one side of the wall, although the walls will share the same studs.

Fortunately, the resilient clips and channels will absorb most vibrations as they hit the drywall.

Acoustic Decoupling Weakness

While acoustic decoupling plays an important role in sound isolation, it has its own downside: Resonance.

A decouple wall will give the best results in attenuating higher sound frequencies but perform poorly in isolating low frequencies.

The air inside the decouple cavity acts like a spring, resulting in resonance. With resonance, the performance of a decouple wall is worse than without decoupling.

In theory, lab tests and decoupling only attenuates above the low-frequency resonance in the real world.

For example, with a resonance of 62 HZ, the wall decoupling only helps above 99 Hz and significantly hurts sound performance below this frequency.

acoustic decoupling
Source: Tmsoundproofing

From the hypothetical graph above, you can clearly see that a solid mass wall gives better sound transmission loss (decibels) for frequencies less than 63 than a decoupled wall.

Addressing Decoupling Resonance Problem

You are going to get the best results at higher frequencies and poor performance at lower frequencies with decoupled walls unless the resonance is addressed.

Below are the different ways to help address the resonance in decoupled walls.

Adding Mass

As highlighted in the previous soundproofing methods, adding mass to a wall can significantly help block sound and vibrations from pushing to the other side of the wall.  The more the mass is added, the hard it becomes for a wall to vibrate.

You can add mass to the stud walls by using a layer of mass-loaded vinyl or drywall which takes up less than 1/8 inch of the wall space.

Acoustic Dampening

Acoustic dampening can be easily achieve using an acoustic sealant such as a green glue noise-proofing compound between layers of drywall.

Green glue compound is visco-elastic and dampens sound by converting it to heat, reducing the amount of sound that leaks in or out of the structure.

In addition, green glue is highly effective in dealing with low-frequency sounds, so adding this sound dampening material on your decoupled wall will go a long way in eliminating resonance.

Acoustic Decoupling Applications

Acoustic decoupling is used in planes to help reduce cabin noise and provide passengers with comfortable air travel.

Both aerodynamics and the airplane itself produce external noise on a flight.

Because commercial jets reach very high speeds, winds whipping around the airplane produce significant noise.

On the other hand, jets are stocked with hydraulic actuators, pumps, electrical equipment, and so much more, which produces a constant whirr of the engine.

The amount of noise generated requires insulating material with high acoustic efficiency.

High-quality acoustic decoupling materials such as non-woven absorbers and mass-loaded flexible barriers are used together or independently in the aircraft.

Below is a basic diagram illustrating how sound is absorbed and blocked by different acoustic decoupling materials.

acoustic decoupling materials
Source: Duracote

As you can in the image above, acoustic decoupling on one side reflects some amount of the sound. The non-woven material inside absorbs some noise that goes through the first barrier.

The second barrier also reflects some of the noise not absorbed by the middle layer. These three layers work together to ensure that the minimum amount of sound leaks to the other side of the wall.

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