Yes, your sketch is correct.  Just for further information, the reason for the diverging cone cross-section being downstream is it helps reduce noise.

Craig Berland

Thanks, LML!  I appreciate your help with the question of the orientation of the sonic venturi.  I've sketched a longitudinal cross-section of my sonic venturi (attached) and indicated the direction of flow, as I understand it.  If this is correct, then the venturis were installed backwards.  I will change them around.
Barry Knotts
LIV-P, Conti TSIO-550, Perrysburg, Ohio