"Why does music 'speak' to our emotions?"
Music is an interesting concept if you break down its parts. You take sounds, form them in a specifically timed rhythm, pair them with other sounds, and hopefully you've made something that will affect its listeners. Music "speaks" to such a broad range of people because there's so much to choose from. Where you have hip-hop fans listening to the likes of Tech N9ne, you've got music specifically chosen by that artist that sound techno and trance influenced. The intermingling of genre's makes for an interesting listen as far as being a consumer is concerned.
Though a specific sound may be popular, it's individualism that gives that particular sound a stand-alone complex. For example, you have an artist who is suffering great personal tragedy in his life outside of music and the music he creates is full of both depression and hope simultaneously. Whereas you give another artist on the come-up in his career, high-sailing from doing big numbers with his records and his music is self-assured and maybe even a little arrogant.
All music is created with a subconscious emotion already attached at its inception, though an artist may not be aware. Writing music, be it lyrics coupled to a beat or the beat itself, can be so uplifting and at the very same time heart-breaking because that song is reflecting everything going on outside of the music.
All in all, music is a great therapeutic tool and a gateway to memories. Music made passionately and with an exact focus is a treat not only to the creator of the piece, but to the fans; the people who demand energy from an artist and continue to make music one of the few universal forms of communication.