absorption – megasorber 4-fold approach (abcd)
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.
sound energy reduced by absorption
Hear how megasorber acoustic foam panels have effectively reduced the reverberation noise in a large hall:
How is the noise absorption performance of materials rated?
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.
How are NRC or αw obtained?
- The Reverberation Room Method (ISO AS ISO 354 or ASTM C423).
- The Impedance Tube Method (ASTM C384). Also known as the standing wave tube method, 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 applications are much closer to that existing in the reverberation chamber than to almost perpendicular incidence, this method gives absorption coefficients that are more meaningful to the application than those obtained with the impedance tube.
Megasorber’s alpha cabin is a compact reverberation testing chamber that uses the Reverberation Room Method.
How can the NRC or noise absorption coefficient exceed 1?
There are many explanations. We summarise as follows:
- 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 room, absorption is calculated in ‘Sabins’.
- The noise absorption coefficient is then calculated by Sabin It is not a percentage as calculated in the Impedance Tube test method.
- We have noticed that the numeric calculation of the Sabin equation provides a sound absorption coefficient (or NRC) above 1 for our highly absorptive materials when tested in NATA certified.
- 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.
What makes Megasorber’s absorption products unique?
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 that breaks down the soundwave into small components and 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 shows a solid substrate, such as a wall or ceiling. Soundmesh® G8 is not only acoustically transparent but also engineered to have acoustic impedance tuned specifically to provide superior noise absorption.
As an example, comparison tests were conducted on 25mm thick acoustic foam, with and without the Soundmesh G8 facing. The test results are shown below.
The unique noise absorption mechanism of Soundmesh® G8
Test results on 25mm acoustic foam with and without Soundmesh® G8 facing
It is evident that:
- Soundmesh® G8 boosts the Noise Reduction Coefficient (NRC) from 55 to 0.85, an 54.5% increase in acoustic performance for the same thickness.
- Significant increase of noise absorption in the low to mid-frequency range, especially in the 250Hz to 2,000Hz
- There is no decrease in noise absorption at the high frequency, such as frequencies between 3,150Hz to 5,000Hz.
Soundmesh G8 boosts sound absorption of the base material. As a result, Megasorber acoustic panels provide superior sound absorption capacity. The unique features of Megasorber acoustic panels are shown in the schematic drawing.
Megasorber sound absorption panels
megasorber sound absorption products
- Non-combustible sound-absorbing fabric: Soundmesh® G8 is a thin, unique fireproof and sound-absorbing material.
- Lightweight acoustic foam panels: Megasorber FM & FG ranges combine hydrolysis-resistant acoustic foam with Soundmesh® G8.
- Acoustic boards: Megasorber PN series are acoustic boards specially designed as drop-in ceiling panels and acoustic backing for timber slats.
- Acoustic polyester panels Megasorber P series: utilises the unique
Soundmesh® G8 facing on acoustic polyester to further enhance the acoustic performance.