If you're way in the back in a big concert hall, you can definitely notice the lag, but it's not a big deal. The problem would be if different instruments reach

If you're way in the back in a big concert hall, you can definitely notice the lag, but it's not a big deal. The problem would be if different instruments reach your ears at different times, and since the closest seat is still a considerable distance from the audience, you're not going to be hearing sounds more than about ~20ms apart. The reverb of the hall also mushes everything together. The problem you describe is a very real problem, however, for the musicians themselves. If you're sitting in a big orchestra and you try to index your playing off someone sitting on the other end of the orchestra, you will not be in time. That's why there's a conductor, so that the orchestra can be synchronized at the speed of light rather than of sound.