ITS marketed an exhaust silencer to limit the noise of a civil works machinery engine, in this case a drilling machine, being, like a crane, a concrete mixer, a bulldozer, a hydraulic mechanical shovel, a scraper, a grader, or other handling equipment - in addition to construction trucks and motorized dumpers - the recurring cause of neighborhood complaints about noise pollution, when their soundproofing level is insufficient (vehicles noise [1] which may, in the context of construction sites, be superimposed on other sources of noise pollution [2]).

For such civil works machinery, the noise emissions - which are combined with other construction site noise that it is sometimes difficult to limit (horns, e.g. machinery movement in reverse gear, noise from other equipment and hardware (e.g. jackhammers, crushers) are variable (e.g. in level and frequency) depending on the characteristics of each, being linked to the works for which they are used.

All these sound emissions have - often - one point in common, however, linked to the recurring presence of an engine, noisy by nature, for which, in particular taking into account the richness of its sound spectrum in low frequencies, the effectiveness of acoustic screens such as those sometimes delimiting the sites is not satisfactory - in terms of limiting sound propagation - (the mobility of civil works machinery, leading to them often moving at a great distance from these anti-noise walls, given their height) and requires soundproofing actions at the source :

  • for the heat engine casing: a cowling is required, the transmission of airborne noise of which must be sufficiently limited, despite the presence of openings necessary for ventilation. The presence of soundproof louvers is then necessary, and the implementation of a sound-absorbing lining on the inside of the panels constituting the enclosure is desirable, to limit the amplification of sound levels (compared to a free acoustic field) inherent in the implementation of a physical limit to the propagation of sound waves (obtaining, in a wide frequency band including low frequencies - at which the level of sound power emitted is rarely negligible - a high absorption coefficient - all as a significant sound reduction – moreover with thin materials, is not always easy, nor is the achievement of an appropriate decoupling to limit the propagation of mechanical vibrations, although this is necessary for soundproofing efficiency)
  • for the exhaust: a silencer is necessary, which can be reactive (i.e. based on changes in geometry - e.g. the cross section - of tubes, perforated or not and on changes in the direction of sound propagation), dissipative (i.e. whose performance is linked to the presence of a porous material - in general: fibrous -) or hybrid (i.e. combining the two effects). A compromise must be found between the acoustic performance (which must be sufficient over the often-extended frequency range) and other varied considerations such as the total pressure loss, size, weight, durability (e.g. when subjected to bad weather). In this respect too, the limitation of vibrations by an appropriate device is required.

Regarding the exhaust in particular, when an existing silencer is kept, and when it is then a question of fitting (in series) a second (to limit the noise of a civil works machinery engine by overcoming the shortcomings of the first in terms of acoustics), the sizing of the second (silencer) is particularly delicate :

  • the ideal place for the installation of a silencer is already occupied and it is necessary to find another one, being compatible with the lay-out of the mechanical components of the machinery, which is sometimes not possible without addition of connection accessories (straight lengths of pipes, elbows) which make the exhaust line more complex
  • the original exhaust silencer (regardless of the principle underlying the effectiveness of the soundproofing device) has (always) been designed without taking into account the possible (future) installation of an additional noise limitation device (i.e. has been foreseen with a total pressure loss at the maximum of what is possible for a normal engine operation taking into account the aerodynamic network between the engine outlet and the end of the exhaust line), which has the consequence that the total pressure loss available for the new device (silencer and associated connecting pipes) is almost zero

Finding a compromise between noise attenuation and other constraints is then necessary: this is what was done on the occasion of the project in question, and there is no doubt that the quality of the design and manufacture of the device for lowering the sound level that has been delivered - with support cradles with anti-vibration mounts, upstream connection piping (with fixings by flanges), downstream elbow (removable) with anti-rain valve - will give satisfaction, like other exhaust silencers marketed by ITS to limit the noise of combustion engines in the context of many other more or less similar projects (including those relating to stationary engines e.g. generator sets for which the power is measured in Megawatts, and which sometimes include the realization a tall chimney).

[1] in Europe, Directive 2000/14/EC on noise emissions into the environment from equipment intended for use outside buildings is applicable

[2] in France, specific regulations apply to worksites subject to declaration or authorization

Preservation of acoustic environment

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