The Sound Designer is responsible for creating an appropriate sound plan, detailing where any live band is to be placed (in the orchestra pit or visible on stage within the set), and how microphones are to be used to allow any band and cast dialogue or singing to be properly mixed. If the cast will be wearing radio microphones, the Sound Designer may want to discuss with Costume Designer how the microphones will be hidden within the costumes, especially if quick costume or microphone changes are necessary.
Some directors will have a very strong view about the overall design (e.g. using radio microphones or not), whereas others will give their designers a greater input into creating the sound design for the show. It is normally left up to the Sound Designer to decide whether they also want to take on the responsibilities of Sound Operator during performances.
The Sound Designer is also responsible for sourcing or making appropriate sound effects that the show requires, and ensures that they fit in with the overall look and design of the rest of the show. Occasionally they may need to discuss with the Set Designer and/or Technical Director where speakers for sound effects can be hidden within the set.
For best results, the Sound Designer should work with the other designers to ensure the sound design is consistent with the overall design ideas, especially with regard to placement of the band if they are on stage. A production will look a lot better if each designer is following a consistent thread and taking into account of the look and atmosphere being created by the other designers.