Innovative hybrid silencers with active noise control

Currently, KFB Acoustics is in the process of conducting a project consisting in the development and implementation of an innovative line of new generation silencers. The product will be used in all industrial flow installations with very high gas flow rates and temperatures up to 300 degrees Celsius. The fans that generate flows in such installations at the same time cause high noise levels in these ducts. At the other end of the duct, this noise in turn is radiated into the environment, propagating over long distances and reaching local homes.
This disrupts the comfort of life for people and animals in the vicinity of the plant. In conditions of extremely high temperatures and flow velocities, it is very difficult to design acoustic silencers for such ducts, which at the same time: withstand the unfavorable conditions in the duct, suppress noise to a sufficiently low level and introduce pressure drops not exceeding the permissible values. Commonly used baffle silencers can effectively fight noise in the medium and high frequency range (figure 1B). Their main disadvantage is the introduction of relatively large pressure drops to the system and often too little sound attenuation in the low frequency range. To achieve the desired results, baffle silencers must have large dimensions and large slits to meet the pressure drop requirements.
This is associated with high costs.

figure 1.

The designed silencer (figure 1C) will be an alternative to baffle silencers. Unlike baffle silencers, the Rocket Active silencer will introduce lower pressure losses, while the acoustic parameters will be maintained at a similar level as in the case of baffle silencers – thanks to the use of specially designed acoustic foams, which will also be resistant to the difficult physical and chemical conditions in the duct. The problem of noise suppression in the low frequency range (especially tonal frequencies associated with the operation of fans) will be solved thanks to the use of the active noise reduction (ANC) system. ANC works by muting the primary noise source by interacting primary noise with artificial, additional sound generated by electro-acoustic transducers. The exact form of “anti-noise” sent to the transducers is determined on the basis of advanced digital signal processing algorithms that react to all changes in the primary noise source on an ongoing basis (e.g. change in the blade passing frequency, increase in temperature, which affects the speed of sound and delays in the duct, change in the characteristics of microphones and speakers as a result of stagnation). Despite the fact that the designed silencer uses active solutions (and therefore requires electrical power to supply all electronics), it will be characterized by simple assembly, not requiring much interference in the mechanical structure of the existing installations. Thanks to the combination of an innovative shape, materials and the ANC algorithms used, the dimensions and weight of the designed silencer will be much smaller compared to classic silencers.