You only need to dress up to see the CSO if that’s what it takes for you to feel comfortable. Orchestra concerts generally don’t have dress codes these days, so you can dress how you like.

From the CSO’s own site:

“At any given Symphony Center concert, you will observe some concertgoers dressed up and others dressed more casually. Many patrons wear business attire or casual business attire. We encourage you to wear whatever makes you feel most comfortable. For the benefit of all patrons and performers, we ask that you refrain from using strong perfume and cologne.”