Well some people believe that music doesn't really affect plant growth while others believe that different genres of music enlists different reactions in different types of plants.
Different studies have been done to determine the effects of music on plants and none have truly been conclusive. As of now, some researchers believe that it's not really about the sound of the music, but it's more about the vibrations that ensue from the music. They believe that the vibrations cause movement which in turn causes the plant to produce more nutrients. They also believe that the type of music used is key to maximizing plant growth, favouring softer music like classical music and pushing against rock music which causes extreme vibrations in the plants which isn't conducive for any type of life form.
Other researchers believe that more study has to be done with even more controlled environments to truly determine if music has any effect on plant growth, but as of now, the theory of music causing favourable vibrations in plant cells is your best bet as to how music affects plant growth.