Noise pollution?

Effective sound insulation is an essential requirement for modern lifestyles. Excessive noise can increase stress, hinder speech and affects well being. Check out how Roxul can make a difference in reducing noise levels through its sound proofing solutions.

Roxul stone wool consists of fibroporous basalt stone with air-filled interconnected spaces. Because of this structure the stone wool has obtained excellent acoustic properties, as they significantly diminish occurrences of vertical sound waves on wall surfaces. The result of this is improved room sound insulation and material sound absorption with a reduced reverberation time, thus lowering the sound level in adjacent rooms.

Therefore, insulating with Roxul stone wool controls unwanted sound or noise; and provides privacy and a conducive environment for working and living space.

Sound Reduction

When a portion of sound incident upon a building element, part of it will be reflected while the rest will be transmitted through the element. The fraction of incident transmitted is called transmission coefficient. The sound reduction index is defined in terms of transmission coefficient.

Transmission coefficient           =            sound transmitted                                                                 ---------------------
                                                              sound incident

The sound reduction index of a roof is measured in a laboratory by placing an element in an opening between two adjacent reverberant rooms. Noise is introduced into one of the rooms, called the source room. Part of the sound energy is transmitted through the test element into the other room, called the receiving room. The resulting mean pressure levels between the source and receiving room is measured.

There is a similar rating developed by ASTM, known as STC (or Rw). This rating uses a slightly different frequency range, 125 – 4000 Hz instead of 100 – 3150 Hz. It also includes the limitation of having no points at more than 8dB below the rating curve in any one-third octave band. In general, the two ratings are interchangeable and will give the same value or value difference of 1 or 2 points.

In Roxul, different roof construction tests have been conducted in a laboratory to achieve a range of Rw (or STC) results. Hardrock, a specially developed roof board, was used in the roof construction to provide acoustic, thermal and fire insulation.

Following are constructions typical of twin skin metal roof. Rw/STC 43 to Rw/STC 46 was achieved without the use of any other high mass materials such as gypsum and cement boards in the construction. Rw/STC 50 was achieved by using an additional layer of 12mm thick gypsum board in the construction.

The roof constructions with perforated metal decks as the bottom layer and specially cut infill helps maintained a comfortable level of sound internally. These constructions are ideal for auditoriums, exhibition halls and indoor stadiums, where a perfect level of reverberation time is required.

View the cross section drawings of the roof constructions and corresponding test results below.

Sound Absorption

Most building materials have some form of sound absorbing properties. Sound absorption is defined as the incident sound that strikes a material surface and does not reflect back. Sound absorption is different as compared to sound barrier. A concrete wall is a good sound barrier but will reflect about 96% of the incident sound, thus making it a poor sound absorbing material.
 
When sound waves strike a sound absorbing material, the sound waves causes the fibres or particle makeup of the absorbing material to vibrate. The vibrations create tiny amounts of heat due to friction and thus sound energy is then converted to heat energy. The more porous a material is, the more it is sound absorbent. Nevertheless, for effective sound absorption, the material should not exceed a certain level of porosity.
 
Frequency level plays an important role in the effectiveness of sound absorption. A higher frequency level allows for a thinner sound absorbing material, whereas a low frequency often requires thicker materials due to the longer wavelengths of the frequency.
 
Roxul Hardrock roof boards tested for sound absorption according to ISO 354 (Measurement of Sound Absorption in a Reverberation Room) showed a remarkable performance on its own as well as when tested in a perforated metal roof system.
 
The first test was conducted on 50mm thick Hardrock, the result achieved was Alpha w : 0.90. Then subsequently tests were conducted on a system which incorporates a perforated metal deck filled with low density stone wool infill. One system has 50mm thick Hardrock and the result achieved was Alpha w : 0.80. Another system consists of 100mm thick Hardrock and the result achieved was Alpha w : 0.85.