My husband does not want to pack a dress jacket while traveling. We would like to attend a classical music concert (not opera) while in Vienna. What is the "acceptable" minimum dress standard for men in Europe? Would nice pants and dress shirt be ok?

You will see everything. Nice pants and a dress shirt will be fine.

I don't ever want to pack a jacket (and tie)--my suitcase is full enough as it is, but I do if I'm planning to attend a concert or the opera. While I realize I don't have to, I feel it's dissing the performers and the venue if I don't.

Same as at home, presuming you've ever been to a classical music concert in a large city in a standard venue or concert hall. Other than that, there are tons of classical music concerts where you could where anything, like free ones ion churches or something.

Opera isn't the same thing as some random classical music concert, which could be anywhere, as I said.

A very famous orchestra conductor (an old man raised in the old British colonial tradition) once told me: I do not understand how could you leave for a foreign land and not to pack a jacket and a tie. You never know who you will met and where you could end.

[He was very angry as he managed to have me and a group of my colleagues invited for dinner by a group of influential people and it turned out that all people but me did not have jacket and a tie. But the point is well taken. - He added: how heavy is a tie?]

I would add: part of the entertainment of attending a concert in Vienna is dressing up. You can see people on trams going to the opera in black tie. I have seen better dressed persons in Austrian concert halls than in, say, the Italian president official residence or the Vatican. - Of course this applies to high level concerts, not to tourist traps.

We attended an opera in Vienna and the dress ranged from men in cloaks through us in casual pants and
Tops to jeans . I certainly didn't feel inappropriately dressed.