A friend is getting married on rosh chodesh and I am hosting a sheva brachos in the week, am I allowed to put on music or even to play live music?
It is controversial if it is permitted or not. If however it is the norm in your area to have music during sheva brachos, then it would be permitted.
Igros Moshe O:CH 1 159, 2 95 D:H U’bdvar, Avnei Yoshpe 1-111 are leneint, Shevet Halevi 3-157 is stringent on this, R’ S. Kaminetsky (Kovetz Halachos 9-7 questions if it permitted, but sounds like he is leaning to be stringent, also see Daas Torah 493-3 D:H V’roisi. However see Ashrei Ha’ish O:CH 3 chap. 65-21 in the name of R’ Eliyashiv that it is permitted for those who usually have music at sheva brachos.