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Geschäftsführer: Jon Ander Lopetegui Galarraga.
Adresse: Industrialdea zona A - parc. 35, 20159 Asteasu, Gipuzkoa, Spanien.
Handelsregisternummer: A-20101150
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Duct isolation

Duct isolation

A poorly isolated duct transmits vibrations and noise, this can have an undesirable result


The correct isolation of machines provides a reduction in the vibration and noise levels in the rooms around them. However, to achieve an optimal level of isolation it is necessary to isolate all the elements connected to these machines.

These connections can act as a physical path for vibrations to travel, this is an area which is often overlooked and can have an important impact on the final result. In addition to the machine itself this article focuses on the importance of duct isolation.

A poorly isolated duct transmits vibrations and noise, this can have an undesirable result in which the isolation level of the machine itself is reduced due to poor isolation of its connecting ducts (both liquid and exhaust).


A common method of isolating ducts and pipework is to suspend them on acoustic hangers, on either side of the anti-vibration element these hangers typically use a metallic threaded rod for their connection with the element to be isolated.

The correct installation is crucial to ensure that acoustic bridges are avoided. The below images demonstrate the importance of having the threaded rod correctly centered to ensure that it does not make contact with the metallic sides of the hanger, this would bypass the anti-vibration element and generate an acoustic bridge.

ACOUSTIC BRIDGE-Incorrect Installation Correct Installation
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AMC Mecanocaucho® recommends to use hangers that combine springs and Sylomer® (SRS+ Sylomer® for the cases with higher loads and ST + Sylomer® for cases with lower loads).

The advantage of these hangers is that they comprise of two stages of anti-vibration elements ensure the best isolation. For low frequencies they have a first stage with a steel coil spring and for medium-high frequencies they have a second stage with a Sylomer® pad.

In most cases the isolation of ducts is achieved via hangers which are directly mounted from the ceiling (or other hanging structure) above. However for some cases where this is not a possibility the use of mounts which are supporting from underneath is an option, in these cases a common solution is the use of additional metal profiles on which the springs are placed, as shown in the image below.

For these cases the solution recommended by AMC Mecanocaucho® would be the same as in the case of springs suspended from the ceiling, i.e. to use mounts that comprise of two stages (spring + Sylomer®) to absorb the frequencies across all ranges.

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In the case of small ducts and pipework it may not be necessary (or possible) to use installations such as the previously described. In these situations, a simple solution to isolate the ducts is to use the Akustik Pipe type Omega mounts.

These mounts are made of Sylomer® and their holes can be adapted to different dimensions of ducts.

Finally, in addition to the mounting of the ducts inside the room it is also necessary to isolate them when they pass into another room through the walls or ceilings. This is necessary since an acoustic bridge is generated with the wall or ceiling that would transmit the vibrations through the building structure, this can highly reduce the isolation achieved through the previously described solutions.

It is necessary to decouple the ducts from the wall installing Sylomer at the perimeter

To do this, the steps to follow are the following:

  • Place a Sylomer sheet in the perimeter of the hole.
  • Make a first bed with polyurethane foam.
  • Lay the duct.
  • Fill the remaining hole with more polyurethane foam.

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