-If one is invited to a wedding at a time when they are observing Sefira, while the one making the wedding observes the “other half” of Sefira and is thus permitted to make a wedding, he/she may attend the wedding, listen to the music and even participate in the dancing. (See Igros Moshe Orach Chaim Vol. 2 Siman 95)
However, taking a haircut or a shave in honor of the wedding is prohibited unless not doing so will be embarrassing and cause you not to go to the wedding and thus prevent you from performing the Mitzvah of bringing joy to a bride and groom. (ibid.)
-If during the days that you do not yet observe Sefira, someone who is observing Sefira enters your home, car or other area where you are listening to music, it isn’t necessary to close the music. However, that person may not deliberately do this in order to hear the music.
Likewise, it isn’t necessary to worry about your neighbors, who may be observing Sefira now, hearing the music from your home, as long as it’s playing at a normal, acceptable level. (This was the Psak of Rav Moshe Feinstein regarding one who is in the year of Aveilus for a parent R”L that his/her family members may play music in the home, and surely that is the Halacha regarding Sefira. Quoted in Sefer Shiurei Halacha from Rav Shmuel Felder Shlita, Posek in Lakewood, NJ).