this invention provides a two - stage phasing plug located within a compression driver . the two - stage phasing plug housed within the compression driver may be coupled to a horn . the two - stage phasing plug includes first and second phasing plugs . the advantages of having a two - stage phasing plug is that the first and second phasing plugs may be simpler to manufacture , cost less and the overall dimensional tolerances may be tightly controlled . the higher dimensional tolerances may be obtained because the first phasing plug may be made from a unitary work - piece , and therefore , may be tooled and cut in the same machining set up . this allows the unitary work - piece to be machined and cut very accurately when compared to assembling separate components together during the manufacturing process . since the most dimensionally critical area is the rear side of the first phasing plug , the tolerances of the second phasing plug may not be as critical . thus , a more expensive material , such as steel , may be used for the first phasing plug , and less expensive material , such as plastic , may be used to manufacture the second phasing plug .