I am a “charedisha Satmer yungerman.”
May I listen to music on the sefirah days to be able to work better?
If this will help you to work better, it is permitted to listen to music.
It is preferable that the music should be calm and soothing, and not fast music appropriate for dancing to.
It is permitted for somebody whose livelihood depends on playing musical instruments to play music (to practice or for goyim) during the Omer period. Rav Moshe Feinstein rules (Iggros Moshe, Orach Chaim Vol. 3, no. 87) that it is permitted to study music, or to teach music, when one does so for reasons related to one’s livelihood, and not for pleasure (see also Seder Pesach Kehilchaso, Chap. 12, no. 16; Tzitz Eliezer Vol. 16, no. 19).
In a similar sense, in the case of the question, if the purpose of the music is not for pleasure but rather for helping a person concentrate in his work etc. one can be lenient.
It is better that the music should be soft, in which case the custom will not apply in any case (see Shoalin Vedorshin Vol. 4, Chapter 37 concerning soothing or emotional music; see also Shut Maharam Schick, Yoreh De’ah 368, concerning listening to “sad music” during a personal aveilus period).