As a post-script to the above, as it happens I was sitting at the back of the tent for the Tickled Pink ceilidh with a sound meter (I was showing the iPhone SPL meter app to a friend).

It measured 90-91dBa - that's about the same volume as a domestic hairdryer.

This is legally allowed in the workplace for up to 8hrs a day. Even then, this legislation doesn't cover the audience at a music event.

Those are the facts.