My brother an I have studied the laws of the Omer from rabbis and sites like http://www.torahmusings.com/2011/05/music-during-sefira/ and we have an accepted practice of not listening even to recorded music during the Omer.
However, he is observing the first "half" of the Omer this year and I am observing the second half.
Because I am a younger brother, it is my job to be difficult and his job to be mean to me and this leads to fights. While we are arguing, I, during the first half of the Omer, turn the radio on because I know that music will give me joy and lead to dancing and will stop the argument.
Does he have an obligation to leave the room (to abide by his practice), or must I turn the radio off so I am not creating a michshol even though I am just following my practice?