Provided is a method of assembly for a noise suppressor using specific welding and assembly procedures. The shaft extends along the long axis and is rotatably supported in the housing for rotation relative to the housing through an angular range including one hundred and eighty degrees to a predetermined maximum angle. Using the impeller module embodiment of the present invention, the anti-leak rubber plug shall no longer in need of forming a shaft hole, so as can structurally solve the long-suffering liquid leakage problem of the snow drop water ball and prolonging its service life. In some embodiments, the surfaces are spherical, conical, parabolic, or other non-planar forms.