Breathable Sound Damping Wall

Noise is an unwanted and unnecessary sound that is loud, disturbing, and unpleasant to hear produced by different sources from the environment. The Breathable Wall provides for a lot of air movement while blocking light, allowing the wall to keep the same cooling and ventilation. Since water can be both gas and liquid, there may be a chance where it lands on the fabrics in the indoor environment which causes the building to be damp, condensation or mouldy.

Soft materials often act as good acoustic insulators i.e., absorbing the majority of the sound, whereas dense hard materials like metals mostly reflect. That is why sound damping materials are made of soft insulators.

In this paper, after researching the properties of sound and the mechanism of breathable walls, the team proposes to increase the use of breathable walls for a better surrounding and environment.

1.1. What is Sound?

There are five basic properties of sound wave; Wavelength, amplitude, frequency, period, and velocity. Sound can be measured by Sound Absorption and Sound Transmission Loss.

In Sound absorption, it determines the amount of sound that has been absorbed by the material or structure. When sound passes through a medium, it is absorbed — captured by the medium’s molecules. Some of the sound wave’s acoustic energy is converted to heat by the medium. The acoustic energy of the sound causes the molecules in the medium to vibrate, which is one way this happens. As for sound transmission, it determines the amount as sound that has been reflected by the material or structure. When sound collides with a barrier, vibrations’ energy is transferred and reflected from the material.

1.1.1.   Factors Affecting Sound

• Helmholtz Resonator for Sound Absorption

Source: ScienceDirect

A Helmholtz resonator consists of a cavity with a stiff wall with open holes called the neck that produces a single acoustic resonance whereby sound waves are able to vibrate or travel easily. The broadband and substantial absorption of sound at low frequencies uses a soft-walled chamber with a hollow neck and a compliant Helmholtz resonator. Hence, at a resonance frequency, Helmholtz resonator is able to absorb a maximum amount of sound energy.

• Mass Law and Flanking for Sound Transmission Loss

These are the factors affecting sound transmission loss. An assembly’s component layers’ mass per unit area is an essential physical parameter affecting airborne sound transmission loss through it. In specific frequency ranges, the “mass law” is a theoretical rule that applies to most materials.

Flanking paths are less evident sound channels in an inefficient design that can transmit more sound energy than the straight channel via the common wall or floor.

There are other factors affecting sound absorption and sound transmission like geometric spreading, atmospheric effects, and surface effects. The factors are:

1. Density: Density and SA are directly proportional to each other. When the apparent density is high, the number of fibres increases per unit area. The energy loss rises with increased surface friction, which raises the coefficient of sound absorption. Less open and denser construction absorbs low frequency sound (500Hz). For frequencies above 2000 Hz, the denser structure works better.
2. Effects of Stiffness: Stiffness and STL are inversely proportional to each other. Schematic loss of transmission of rigid materials shows dips, particularly in frequency ranges where the losses in sound transmission are lower than those indicated by mass law. Materials with very low rigidity such as plate plumbing are efficiently non-coincidental.
3. Thickness: Thickness and SA are directly proportional to each other. Sound absorption is acquired when the thickness of the material is around 1 tenth of the sound’s wavelength.
4. Porosity: Porosity and SA are directly proportional to each other. The sound wave must penetrate the porous material in to dissipate the sound through friction. This means that the sound should be damped by sufficient pores on the material surface.
5. Fibre Diameter: Fibre size and SA are inversely proportional to each other. The sound absorption coefficient is increased as the fibre diameter is decreased. Thin fibres are able to travel on sound waves easier than bulky ones.
6. Airflow Resistivity: Airflow resistivity and SA are inversely proportional to each other. The amplitude of the sound is reduced by friction as the waves try to traverse the convoluted passageways when these materials enter.