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Soundproofing: Block it or absorb it?

Have you ever stood still in a rainforest to listen to the beautiful silence? Sometimes the only the sound you will hear will be the silent hush of the trees above or the occasional chirping of a bird.

This lack of sound is not only explained by the absence of humans and their noise, but by the architecture of the rainforest itself. The density of the vegetation and the lush carpet of decaying plant material create a sound absorbing environment, leaving fewer soundwaves to travel freely.

When creating spaces that provide acoustic comfort, it is important for architects and acoustical consultants to take cognisance of how sound behaves in a contained environment.

When soundwaves hit a barrier, three things can happen:

  • It can be reflected, as in a cathedral where it bounces off the hard walls and gets redirected back to the source of the sound;
  • It can be transmitted, as through the wall from one room to another; or
  • It can be absorbed, as in the rainforest, where it gets trapped in an absorbent material and stopped from travelling further.

Acoustic comfort

Acoustic comfort is defined as a psycho-physical condition where a person, in a specific environment, experiences a sense of well-being in relation to the specific activity that he/she is doing.

Acoustic comfort is achieved by controlling how the sound is reflected, transmitted, or absorbed based on the type of space. Different acoustic treatments will be required in different situations to achieve the desired effect.

There are two acoustic requirements for any space:

  • To provide an appropriate internal acoustic environment by means of sound absorption, and
  • To prevent noise disturbance from outside by means of sound insulation.

To put it simply: if you want to keep the sound out of the room, block (insulate) the sound. But, if you want to communicate clearly or hear clearly in the room, absorption is needed. Sound absorption helps to improve the quality of the sound.

In most spaces, a combination of insulation and absorption works best, so a balanced and appropriate use of both is vital to achieve a favourable acoustic environment.

The perception of sound is not only a personal one. The Building Code of Australia (BCA) contains specific requirements on sound insulation of building components and the Australian/ New Zealand standard AS/NZS 2107 has recommendations on noise level and reverberation times in building interiors.

Sound absorption

Anybody who has moved house would have experienced how differently an empty house sounds to one full of furniture and curtains. These materials absorb sound and in their absence soundwaves will bounce right off the walls and back to the source, resulting in an echo.

Materials that absorb sounds are porous. The soundwaves get trapped in between the tiny fibres or particles it’s made of and are turned into an extremely small amount of heat.

Heavy, dense and smooth materials such as concrete walls may have good sound insulation but have poor sound absorption. In contrast, light, porous and rough materials have better sound absorption but poor sound insulation.

Sound absorption also controls the reverberation time of a room: generally, the higher the absorption, the lower the reverberation time.

The sound absorption property of a material or building component is usually expressed as a single number rating – the values are calculated differently, but these ratings are known as NRC and aw. A value of 0 means completely reflective and a value of 1 means completely absorptive.

Sound insulation

Sound insulation means to block the transmission of air-borne noise from one space to another, for instance from outdoor to indoor, from one unit to another. The sound insulation property of a building component is usually expressed as Rw or Rw+Ctr ratings in dB units. The higher the ratings, the better the sound insulation performance.

A room with hard, dense materials like concrete and glass will provide good sound insulation, but it will result in the sound having nowhere to go. The sound waves will bounce off the walls and reflect straight back to the sound source to produce an echo.

The main ways to improve insulation and minimise sound transmission from one space to another is by adding mass and decoupling.

  • Mass can be achieved through using dense materials, such as specialty plasterboard
  • Decoupling can be achieved through air spaces or air gaps, such as the interstitial cavity between wall layers

Acoustic linings

Acoustic linings are a trusted solution used by architects and designers to absorb unwanted sounds and improve the audio experience within a building.

Acoustic linings are designed with sound absorption and reflection in mind and are added to a room’s surfaces to improve the acoustic comfort. These panels can provide a solution for existing buildings with less-than-perfect acoustic conditions, and they are as easy to install as hanging a picture.

Contemporary acoustic linings such as Cleaneo Adit and Cleaneo Up from Knauf’s Room for Xpression range are not only effective in controlling sound, but can add a lovely decorative element to new or existing spaces.

Knauf Adit Up 2
Cleaneo Up and Adit
  • Cleaneo Adit improves the acoustics in the room while decorating the wall. The panels are very easy to install and can be printed with a design of your own choice. It is the ideal solution for acoustic treatment of existing rooms.
  • Cleaneo Up is a perfect acoustic lining for ceilings. It is supplied with an assembly kit and prefinished in white. It can be painted without compromising on performance and incorporated into the décor of an existing room.
Any questions? Contact us today.