composites – megasorber 4-fold approach (ABCD)

A soundproofing composite consists of sound absorption material and a noise barrier. The absorber-barrier composite combines sound absorption and sound blocking in one single product.

The absorption dissipates the energy from the system. Sound is attenuated by a noise barrier. Through years of research and development, Megasorber has successfully developed a special range of soundproofing composite materials.

composite with high NRC and STC rating

The absorber-barrier composite is designed to provide excellent sound absorption with NRC up to 1.0 and high sound transmission loss, with STC up to 30

high sound absorption capacity – NRC up to 1.0

This is designed to reduce the reverberation inside the room, increasing the speech intelligibility, ie. reducing the echo or reverberation inside the room

high sound transmission loss – STC up to 30

This is designed to increase the privacy between rooms and prevent noise from getting out.

Megasorber CM28 & CM52 composite panels

CAC or STC?

CAC (ceiling attenuation class) explained

CAC is used to evaluate the effectiveness of a ceiling material in attenuating the sound

What is the difference between CAC and STC?

CAC is a two-room test measure of sound that passes from the source room, through a ceiling, across a common plenum and down through the ceiling in an adjacent (receiving) room. It is a ‘double pass’ rating (Standard: ASTM E1414)

STC (sound transmission class) is a single pass rating, measuring the sound reduction from one side of a barrier to the other for walls, partitions etc. CAC is the sound attenuation through the sound absorption mechanism. STC is for sound blocking.

As a result, the CAC and STC are completely different. For example, the same ceiling material has an STC 14 rating when tested using the single pass rating but has a CAC 35 rating when tested with the double pass rating.

The importance of high sound absorption and blocking ratings for office ceiling materials

The above schematic drawing shows two offices with a common plenum.

The top drawing:  a ceiling material with low sound absorption NRC 0.10 and little or no sound insulation properties.

The bottom drawing:  a ceiling material with Megasorber CM28, with high sound absorption NRC 0.80 and a high sound blocking rating STC 24 (or CAC 60).

the effect of high sound absorption NRC 0.80

The source room: reduces the sound pressure level by 5dB(A).  This improves speech intelligibility.

The receiving room: reduces the sound pressure level by 11dB(A). This improves speech privacy.

the effect of high sound blocking STC 24 (or CAC 60)

The receiving room: reduces the sound pressure level by a further 40dB(A), providing total speech privacy.

Using composite absorption & barrier products to reduce noise intrusion

Absorber-barrier composite ceiling material is also extremely useful for increasing speech intelligibility against external sound intrusion. Take the rain-drop impact noise, for example, as shown in the below schematics, Assuming the rain impact noise is 75 dB(A).

The left diagram:  noise reduction through a composite product only, such as Megasorber CM28.  The estimated total noise reduction is about 29dB(A).  The estimated noise level is 46 dB(A) in the office.

The right diagram:  noise reduction when combining the composite product with a vibration damping material such as Megasorber D14 on the roof (see damping page for more information).  The damping treatment on the metal roof panels contributed an extra 13 dB(A) noise reduction.  The combination of the CM28 and D14 provides an estimated noise reduction of 42 dB(A).  The estimated noise level is 33 dB(A) in the office.

CM28 only

CM28 and D14

additional performance – adding an enhancer layer

Enhanced soundproofing is achieved by adding an enhancer or decoupling layer, which keeps the noise barrier separate from the substrate, providing further sound transmission loss.

A schematic drawing of the sound absorber–barrier soundproofing composite is shown here. It consists of three key components:

  1. Sound absorber: this is designed to absorb airborne sound. A suggested sound absorption rating is NRC (Noise Reduction Co-efficient) 0.80 to 1.0
  2. Noise barrier: this is designed to block out the air-borne
  3. Enhancer: this is to create a space between the noise barrier and the substrate, to further enhance the sound blocking effect. It is similar to creating double glazing for windows.

The thickness of the enhancer controls not only the overall effectiveness of the soundproofing composite – i.e. the overall noise level – but also the bass frequency of the effectiveness.

The effect of the enhancer on the overall noise level is demonstrated in the marine engine room insulation below. The engine room has a 75mm composite deck, and above it is the saloon. The engine room noise level is typically around 114 dB(A)

The variations in soundproofing treatments are as follows for comparison:

  • Without the soundproofing composite;
  • Soundproofing composite with 6mm thick enhancer;
  • Soundproofing composite with 25mm thick enhancer;
  • Soundproofing composite with 25mm thick enhancer and double the weight of the mass
  • Soundproofing composite with 100mm air gap instead of enhancer and double the weight of the mass
  • Without any soundproofing, the noise level at the saloon is about 92 dB(A)
  • The sound absorber-barrier soundproofing composite results in a 13 dB(A) noise
  • The increase of the enhancer from 6mm to 25mm results in a further 5 dB(A) noise
  • Increasing the mass layer from 5kg/m2 to 10kg/m2 provides an extra 2dB(A) noise
  • Using a 100mm air gap in place of the 25mm enhancer layer provides an extra 2dB(A) noise.

In summary, the combination of a 25mm enhancer with a mass layer of 5kg/m2 (or 10kg/m2) provides the optimum soundproofing effect in the minimum amount of space. The large air gap gives very little difference in performance.

effect of enhancer layer thickness on the bass frequency range

The effect on the bass frequency of the enhancer layer thickness and the mass layer weight is demonstrated by an engine enclosure built with 16mm thick plywood, lined with soundproofing composites as follows:

1. Mass layer of 5kg/m2, with various enhancer thicknesses as follows:

6mm enhancer 12mm enhancer 25mm enhancer 50mm enhancer

2. 10kg/m2 mass layer with 25mm enhancer

The results are compiled in the graph below

It is evident that the thickness of the enhancer controls the effective frequency range of the soundproofing composites.

Soundproofing composite is only effective above 500Hz with a 6mm enhancer and 400Hz for a 12mm thick enhancer.

This is generally not satisfactory for engine enclosures, such as engine rooms in boats. The enhancer contributes very little to any extra performance when the thickness is less than 12mm.

For a high level of effectiveness, it is necessary to have a 25mm thick enhancer with a mass layer of either 5kg/m2 or greater, such as 8kg/m2 to 10kg/m2.

The greater thickness of the enhancer increases the bass frequency of the effectiveness. Heavier mass layers increase the effectiveness throughout the entire frequency range.

megasorber composite products

  • Megasorber CM28: 28mm soundproof composite with Soundmesh® G8 facing (25mm absorber + 6kg/m2 noise barrier)
  • Megasorber CM52: 52mm soundproof composite with Soundmesh® G8 facing (50mm absorber + 6kg/m2 noise barrier)
  • Megasorber C14: 14mm soundproof composite with Soundmesh® G8 facing (12mm absorber + 6kg/m2 noise barrier)
  • Megasorber C50: 50mm soundproof composite with Soundmesh® G8 facing (25mm absorber + 6kg/m2 noise barrier + 25mm enhancer)

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