When I went there I just wore my normal casual clothes. If you're talking about the blues performances, I think just casual/semiformal attire is fine, but if you want to be absolutely sure then you should call them.
Most concerts are casual to upscale. Younger ppl age 50 and below are blue jeans casual. Ages 50 and and above are dressed.
Casual.
Pretty much what you would normally feel comfortable in visiting most any museum. I visited in November so it was cold and I dressed accordingly, summer may be a different story...
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