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Here you will find blog posts from the SIDERISE team including articles written by our technical experts. Find out more about our products and what’s going on in the industry for acoustic, fire and thermal insulation.

It’s a given we live in a relatively noisy world and many of us like to sound-off about problems with noise pollution in our day-to-day life.

When it comes to buildings and the specification of an acoustic material, then chances are you are looking to solve a noise problem. In the fourth in a series of blogs, Mike Carrick AMIOA, Head of Acoustics at Siderise Group, provides some insight into the effects of material placement and how acoustic materials fall into one of three camps - isolation, absorption and sound barrier.

Step 7 - Understand the effects of material placement

The placing of an acoustic material in a particular area may have differing effects. For example, the placement of a high-mass board around a noise source (acoustic enclosure) will increase the sound levels of the noise source while the mass board will reduce this increased level.  In other words, if a machine had measured levels at 500mm away of 60dB(A) and at 2000mm away of 54dB(A), the installation of a high- mass enclosure spaced on all sides and top at 1m away, would likely increase the level at 500mm away to 63dB(A) or higher due to sound reverberation inside the enclosure. Therefore, a material with a performance of say 20dB Rw would not reduce the level at 2000mm away from 54dB(A) to 34dB(A). It would instead be likely to be closer to 39dB(A) and only a 15dB drop, called an ‘Insertion Loss’. The use of a sound absorbing layer inside the enclosure would reduce the reverberant sound energy and therefore improve the performance of the enclosure.

If a material has an acoustic performance of 20dB Rw, the addition of a second layer directly to the first would not increase the performance to 40dB Rw. It would, based on the ‘Mass Law’, be only 26dB Rw. However, if the two layers were spaced apart, the improvement would be greater than the 6dB for doubling of the mass. The larger the gap, the better the improvement, but as with the enclosure above, the void between the layers is susceptible to sound energy build up due to the reverberations, so again, the use of a sound absorbing layer in-between would help. A good example of this is a plasterboard partition where more layers of board, thicker studs and the use of a mineral wool in the middle all effect the performance of the partition.

Step 8 - Material types, isolation, absorption, sound barrier

Acoustic materials generally fall into three types or categories, a) Isolation b) Absorption c) Sound Barrier.

Isolation materials are generally soft and resilient, such as cork, rubber etc, and are effectively used to break the connectivity of two rigid elements, thus reducing the structural sound transmission via this path. An example would be a shower pump where rotational elements in the pump cause vibrations in the pump housing, which if mechanically fixed to a floor, will transmit these vibrations into the floor. These in turn will radiate noise into the air like a speaker. The use of flexible rubber isolation pads between the pump and floor will significantly reduce this effect.

Absorption products are generally open cell structure materials (for porous absorbers) and reduce the amount of sound energy that is reflected off the surface. Typical materials would include mineral wool and acoustic foams. The sound energy an object emits is a combination of its sound power with direct sound transmission and the reflected sound transmission. For instance, if a mobile phone is playing music from its speaker in open parkland, the noise level will be one level. If it’s moved into a reflective hard surface area, such as a bathroom, and placed on a hard surface at the same volume, the noise level would be significantly higher. Introduction of absorption products into the room would reduce the reverberated sound energy and thus reduce the noise level.

Sound barriers are used to reduce airborne sound energy passing directly through a material or construction and are largely controlled by the mass of the material. A sound barrier would typically have a high mass - solid without open cells - such as a steel plate, plasterboard, barrier mats etc. The use of sound barriers between the noise source and the receiver can typically be in the form of an enclosure, wall or barrier. A typical example would be a stud partition splitting a room in two where the thicker the partition and more layers of plasterboard either side would increase the overall acoustic performance. Single homogenous panels are typically controlled by the ‘Mass Law’ of acoustics, where every doubling of the mass increases the sound reduction index by 6dB. Twin layer systems, such as a partition, with two mass lines and a separating gap (the larger the better) will outperform a single layer material of the same mass. The void between mass layers should be filled with an absorption material to reduce sound pressure build up inside the cavity due to reverberations. 

In my next blog, I’ll look at how specifiers need to investigate material performances and suitability and when armed with all the relevant information will be able to specify the right acoustic product.

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