This Halacha is an excerpt from our Sefer
During the nine days, it is forbidden to play music even for livelihood/Parnasa purposes, even for the sake of gentiles.
May one dance on Shabbos in honor of a Chasan or Bar Mitzvah?
Yes. This applies even by Shabbos Chazon.
May one play music by a Bar Mitzvah; Bris or Pidyon Haben during the nine days?
May one practice music during the nine days?
May a music teacher continue teaching during the nine days?
No. If, however, the teacher is pressed for Parnasa or the students are pressed for time then some Poskim rule it is permitted up until the week of Tisha B’av.
 Kitzur SH”A 122:1; Biur Halacha 551 “Mematin” in name of Peri Megadim “May play for gentiles for Parnasa” and Derech Hachaim “Implies that even according to the Peri Megadim it is only allowed until Rosh Chodesh”
 Piskeiy Teshuvos 551:5 in name of Makor Chaim 551
 Piskeiy Teshuvos 551:13 [Vetzaruch Iyun on his source]
 Zecher Simcha 63; Tzitz Eliezer 16:19; See Mahrahm Shick 368; Piskeiy Teshuvos 551:14; Rav Asher Lemel Cohen told me it is forbidden being that there is no allowance for the students and most people are not in such dire need for Parnasa.