Classical concerts generally require formal attire.

First of all, classical and pop can be compared. The classical music of today is the popular music of that time. Today's popular music will become the "classical music" of that period a few hundred years from now. Whether it is classical music or pop music, the process of appreciating it is a process of enjoying beauty. Secondly, uniform clothing can create a good atmosphere and make it easier for the audience to integrate into the music and appreciate the beauty of the music. Third, wearing formal attire also shows respect for the musicians.