Sound is absorbed by porous materials. The sound wave is trapped and dissipated through these materials. The porous material must not be, therefore, too 'open' or too 'closed' for the sound wave.
In addition, solid or impermeable facing materials must be avoided as these materials (such as aluminium foil, mylar film, etc) tend to reflect the sound and prevent it from being absorbed by the porous material behind them.
Megasorber's sound absorbing materials are engineered to optimize and maximise sound absorption.
In addition, Megasorber employs a unique Soundmesh G8 acoustic facing to further enhance the sound absorption capacity of the Megasorber range of sound absorption materials.
Soundmesh G8 is a patented smart material which breaks down the soundwave to small components, then traps and dissipates the soundwave within the spacer behind it (U.S. Patent No. 8167085, Canada Patent No. 2674986, Australia Patent No. 2009206197). A schematic drawing is shown below with a solid substrate such as a wall or ceiling. Soundmesh G8 is engineered to have acoustic impedance tuned specifically to maximise noise absorption.
(1) The NRC (Noise Reduction Coefficient):
The NRC value is the average of the noise absorption coefficients at four 1/3 octave frequencies: 250Hz, 500Hz, 1000Hz and 2000Hz.
(2) The weighted sound absorption coefficient 'αw':
The αw is determined according to international standard BS EN ISO 11654.
The weighted noise absorption coefficient αw is the single figure rating obtained at 500 Hz. Shape indicators L, M and H are applied to the weighted sound absorption coefficients where the measured coefficient exceeds the reference curve at one or more frequencies by at least 0.25.
L - excess of absorption at 250Hz
M - excess of absorption at 500Hz to 1000Hz
H- excess of absorption at 2000Hz to 4000Hz
An NRC or αw of 0 indicates perfect reflection; an NRC or αw of 1 indicates perfect absorption.
(1) The Reverberation Room Method (ISO AS ISO 354 or ASTM C423).
(2) The Impedance Tube Method (ASTM C384). It is also known as the standing wave tube method. It is commonly used for laboratory testing.
These two methods differ by the incidence angle with which the sound waves impinge on the surface of the material. In the impedance tube, the waves arrive at the surface perpendicularly, whereas in the reverberation room the angles of incidence are evenly distributed.
The absorption coefficients obtained with the two methods differ significantly. If comparative tests of the absorption of different materials are performed, the resulting rank ordering can be totally different, depending on which method is used.
As the sound fields encountered in most of the applications are much closer to that existing in the reverberation chamber than to almost perpendicular incidence, this method gives absorption coefficients which are more meaningful to the application than those obtained with the impedance tube.
Megasorber's Test Cube is a small reverberation testing chamber which uses the Reverberation Room Method.
There are many explanations. We summarise as follows:
(1) Absorption coefficients are derived from the reverberation time difference of a room's absorption, with and without a specimen, divided by the area of the specimen. The room absorption is calculated in 'Sabins'.
(2) The noise absorption coefficient is then calculated by Sabin equation. It is not a percentage as calculated in the Impedance Tube test method.
(3) We have noticed that the numeric calculation of Sabin equation provides a sound absorption coefficient (or NRC) above 1 for our highly absorptive materials when tested in NATA certified laboratory.
(4) We recommend that an NRC of 1.0 is used for any acoustic calculation when a material or product with a reported NRC of exceeding 1.0.
The unique noise absorption mechanism of Soundmesh G8
The test results on 25mm acoustic foam with and without the Soundmesh G8
It is evident that:
Megasorber absorption materials employ multiple noise absorption mechanisms to maximize the total absorption capacity. The range of noise absorption materials is as follows: