Why: Sound supports the emotional impact of the drama, via sad music. It can portray a sad scene by using a minor key. The sound design immerses the audience in the experience.

Where:
there is a sound mixing room at the front top of the theatre called 'Front of House'. Audio is mixed and balanced by a soundman in that room. In musical theatre, an orchestra is seated between the stage and the audience. The conductor faces the stage so that he can coordinate the music to the pacing of the story.

Who: there are sound designers to prepare the methods of creating sound effect, composers, musicians and a conductor for music, and a  sound engineer (known as a soundman) to mix and balance the live sound. The sound man also needs a crew of at least 5 men to arrange microphones and adjust them in case something goes wrong. Some crew hold spare mic or wireless transmitters to pass to performers.
Acoustic engineers are degree holders (or higher) that builds the lecture theatre so that the sound reflects well and sounds good to the audience. 

When: for musical theatre, the orchestra is played live. Some sounds are made by the actor's themselves. Lower budgets use sound made on the spot by props such as sticks. Higher budget productions prerecord their sounds and use a soundboard that plays the individual sound effects by a press of a button.

How: For prerecorded sound, sound effects are recorded in a recording studio beforehand and played back on the day of the live show. For non prerecorded sound, there is a few people that are mic'ed jp, ready to smash sticks or knock rocks to make sounds when the time is right. Musical theatres always have an orchestra playing on the spot, but non musical theatres usually use mp3s directed into the PA system.

Why: To entertain audiences
 To share some stories to audiences.