Sleep is essential in our lives. Unfortunately, many individuals suffer from a lack of sleep and sleep disorders, which negatively impact their daily lives and cause many problems. Feeling negative emotions during the day can be a reason for sleep deprivation. On the basis of a study which explored how emotional states influence sound preferences for sleep, we have developed the SoundAsleep app. After the user answers questions about their emotional state, the app suggests three sounds that can help them fall asleep. We evaluated the app - its impact on sleep quality and more generally how people experienced using it - with twenty participants who used it every day for at least one week. Results from this evaluation further support that a relationship between emotional states and sound preferences for sleep exists. Finally, we suggest new directions for research and development of effective sound-based sleep aids.