I know the sound system is by Clair Brothers Audio out of Pennsylvania. I found this article on u2.com:
And personally for Joe O?Herlihy, using a new sound system designed especially for indoor arenas, the experience has been a technical boon compared to previous tours. ?For me, looking after the sound, it is wonderful to be back indoors again because we are using a new system from Clair Brothers which has made an enormous difference to the sonic proportions and capability we have, far superior to anything before. ?Technically, in one foul swoop, we have a one thousand per cent improvement...?
As if to prove that this is not just some audio-tech enhancement that the audience are oblivious to, he cites the way that Bono is increasingly being quoted word for word in concert reviews: ?Journalists can hear exactly what he is saying, vocal intelligibility has never been as good as this.?
There is an article out there which explains the model they use but the site that has it happens to be down at the moment. When its back up I'll post that here for you.