Resonant cavity devices for reducing noise within a duct in the presence of a gaseous fluid

DETAILED DESCRIPTION The object of the invention is an annular chamber belonging to the second category mentioned above, but which simultaneously offers the following advantages in comparison with known chambers: Simplicity of construction; Small lateral bulk; Large variety of possible shapes of resonant cavities and vents and consequent ease of adaptation, without significant modification, to numerous applications.
The chamber according to the invention is generally characterized by the fact that each resonator opening or vent opens into the corresponding cavity through a duct which is joined to the inner shell, penetrates into the interior of the said cavity, and opens into the channel flush with the inner wall of the said shell.
The volume of said duct thus lies entirely within the volume of the corresponding cavity and results in saving the length of said conduit from the lateral bulk; in view of the ratio of the volumes of the duct and of the cavity, the elevation of the tuning frequency resulting from this arrangement because of the reduced cavity volume being very small and, if appropriate, can be completely compensated for by adjusting one of the numerous other parameters of the acoustical system achieved in this manner.
In a particularly advantageous form of achievement, as to simplicity of construction, the cavities are obtained by dividing the volume enclosed between the shells by means of partitions oriented transversly (that is, arranged perpendicularly or obliquely) to the direction of the flow; the openings of the ducts into the channel consist of slits provided in the inner shell and are substantially parallel to the partitions; the ducts are delimited within the cavities by pairs of lips which are parallel or inclined with respect to each other.
It can be seen that these arrangements make it possible to obtain highly varied configurations in a very simple manner, since at least a portion of one lip of each pair of lips can consist of a portion of a partition or of the inner or outer shell