Triple Leaf Effect

Triple walls have lower sound insulation performance than double walls.

What does this mean? Really do double walls have better soundproofing effects than triple walls?

What a strange thing to do. Considering common sense, don't you think building multiple walls will naturally make soundproofing better?

So why is a triple wall worse than a double wall?

Exposing Acoustical Myths ~ Triple Leaf Effect ~

Since it's a triple wall, you can think it'll be more effective in soundproofing, but it's not

If it's a triple wall, it's less soundproof than a double wall

Single wall

The composition of the soundproof wall is finished by placing a stud in the center, filling the soundproofing material, and attaching a plaster board or OSB plywood back and forth.

Hard wall surfaces such as gypsum boards and OSB plywood are called Leaf.

In the case of a single wall, there is one layer, but it is a double leaf because the Leaf is attached to the front and back.

Double wall

One more wall is installed to further increase the sound insulation effect in the single wall. Then it will be as follows.

Leaf Stud Leaf (air layer) Leaf Stud Leaf

If you look closely at the figure above, the case of a double wall has four Leaves. (Quadruple Leaf)

Two walls were installed, but as a result, they became quadruple leaves.

According to the Canadian Forest Service's soundproofing experiment,

When it's a single wall, the STC is about 36 dB

*STC (Sound Transmission Class) - Average value (dB) measured by frequency band, which means that the higher the number, the better the soundproofing.

When a single wall is erected twice to form a double wall,

The sound insulation performance is increased by about 4 dB becoming 40 dB.

At the beginning of the text, I said that double walls have better sound insulation than triple walls.

However, as explained above, when it is composed of a double wall, it can be seen as a quadruple wall beyond a triple wall.

At this time, let's remove one of the centers leaves in the above situation.

Leaf Stud (Remove Leaf) Leaf Stud Leaf

If you remove one Leaf in the middle like this, it becomes a Triple Leaf.

In the Quadruple Leaf configuration, the STC was 40 dB

If one of the middle leaves is removed and configured as Triple Leaf, the sound insulation capability is increased by 10 dB becoming 50 dB.

One wall (Leaf) was removed, but the soundproofing performance increased tremendously.

But I'm going to remove one more Leaf from the center

Leaf Stud Stud Stud Leaf

If the Double leaf configuration is made, the STC of 56 dB is obtained by going up by 6 dB more than in the Triple leaf configuration.

Conclusion: If you remove the Leafs in the middle after constructing a double wall, the sound insulation performance increases dramatically compared to building multiple walls.

The more materials you don't use, the better the soundproof performance, so both economic and soundproof performance is beneficial.

The biggest reason for this difference in soundproofing performance is the resonance sound.

Because of the resonance between Leaf and Leaf

If the two Leaves are removed in the middle, the resonance sound generated in three places will be reduced to one place, which will significantly reduce the resonance sound.

In a previous blog post, I said that if the resonance noise is eliminated by making it pentagon, the soundproofing performance can be improved by more than 15 dB.

This is exactly the case.

The more walls are erected, the more resonance sounds generated between Leaf and Leaf are increased, and the soundproofing performance gradually decreases.

People generally think that it is a double wall because it has two walls.

But it's actually a Quadruple-leaf composition.

People misunderstand that building a lot of walls will increase the soundproofing performance, so much construction is done, and it should be made into a double leaf configuration to improve the soundproofing performance.

Here is one more tip for getting more sound insulation.

Do not throw away the leaves that were removed when making a quadruple leaf double-leaf, but attach them to the remaining leaf surface. (Put it on so that there is no air layer)

Leaf Leaf Stud Leaf Leaf

In this way, sound insulation performance can be expected from 56 dB becoming 63 dB

Quadruple Leaf Triple Leaf Double Leaf Double Leaf, Double Layer

STC 40 ,         STC 50,      STC 56,.          STC 63

It can be seen that sound insulation performance can be improved up to 23 dB depending on how the same material (soundproof plasterboard) is arranged.

-Ted Kim