1. Music to hear: i.e., you who it is music to hear. sadly: seriously, gravely, with a melancholy mood.

4. thine annoy: that which disturbs you.  —The entire first quatrain of the poem plays with the paradoxical fact that there is such a thing as melancholy pleasure, such as the pleasure we feel in seeing Romeo and Juliet, a tale of woe.

6. unions: i.e., harmonious blending.

7-8. confounds / In singleness the parts that thou shouldst bear: literally, destroys musical harmony by going it alone instead of taking your part in the chorus; metaphorically, destroys potential family harmony by being single.

9-10. one string, sweet husband to another, / Strikes each in each by mutual ordering: —This refers to the double strings of a lute, one of which vibrates sympathetically when the other is plucked.

12. note: music or harmony.

13. Whose: i.e., the strings'.  speechless: wordless.  being many, seeming one: i.e., many voices singing in harmony.

14. Thou single will prove none. i.e., if you stay single you will be worth nothing. .