Music is always a subject for opinion, adoration, dedication and sharing. Music can be a perfect ground for starting a social network. Do it right and your site popularity will skyrocket! Still not dominated by any one existing company music industry offers great opportunities and many niches. Build, say, a Last.fm-like network for indie musicians, public-domain music sharing portal or platform for bands pages.
Maybe take it a bit more personally and create a site about your favorite style, band or musician. Like-minded fans will find it and will join your effort. Discuss gigs and share impressions - bring up pieces your like and share with other admirers!
Dolphin is equipped with a capable "Sounds" module, but you can take it further with BoonEx Market products. Radio plugins, playlists, music-related templates, contests and band pages modules can be a great foundation for a new mega-popular musical community site. Under your full control.