Manufacture of an acoustic silencer

A method for attaching a resonator to an airflow, comprising:

• (A) forming the resonator comprising:
• forming a sleeve insert having:
• a wall, a first aperture in the wall at a first axial distance, a second aperture in the wall at a second axial distance, and a rib having a proximal end at the wall of the sleeve insert and extending outwardly from the wall and terminating at a distal end vertically displaced from the wall, the rib being located between the first and second apertures;
• and
• inserting the formed sleeve insert into an open mold of a blow molding apparatus;
• sliding a parison over an entire length of the sleeve insert;
• clamping the mold over the parison wherein the mold pinches the parsion into the sleeve insert at three axial pinch points, a first one and second one of the pinch points being on the wall and a third one of the pinch points being at the distal end of the rib, the proximal end of the rib being between the the first one and second one of the pinch points;
• blowing a gas into the sleeve insert to bond the parison to the sleeve insert to the three axial pinch points, and with ends of the outer duct extending outwardly beyond ends of the sleeve insert forming the resonator with:
• a first toroidal cavity disposed between the sleeve insert and the outer duct at a location proximate the first aperture, the first aperture providing an entrance to an interior region of the first toroidal cavity;
• a second toroidal cavity disposed between the sleeve insert and the outer duct at a location proximate the second aperture, the second aperture providing an entrance to an interior region of the second toroidal cavity;
• and the outwardly extending rib forming a common sidewall separating the interior region of the first toroidal cavity from the interior region of the second toroidal cavity;
• and
• (B) coupling the one of the outwardly extending ends of the parison to the exhaust manifold.