From the Super Mario Wiki
The Conservatory (Japanese: 音楽室 Music Room) is a room cleared in Area Two of Luigi's Mansion.
After procuring the Key from Shivers in the Butler's Room, Luigi gains access to the Conservatory, where he finds many instruments. Sitting at the grand piano is The Beautiful Pianist, Melody Pianissima. Luigi captures her by listening to her music and answering a question about it correctly. After Luigi captures Melody, the lights turn on and the Key to the Dining Room appears.
The Conservatory houses a variety of musical instruments. The instruments consist of the following: a horn, a harp, a cello, three kettle drums, a xylophone, and a grand piano. All but the grand piano can be activated, causing a tune to be played.
 Ghosts in The Conservatory during the blackout
 Names in Other Languages