For maximum environmental kudos your event should take measures to minimise noise pollution. Usually this is part of the permit conditions anyway but some events will close the main stage at a specific time, limiting noise after, say 12 midnight only to stages which are undercover. This minimises the disruption to surrounding nocturnal wildlife which usually have a heightened sense of hearing for hunting in the dark. Family or one day events may take this one step further and impose a curfew or only have a silent disco operating(Camp Bestival in the UK for example).
All events should offer a quiet zone or chill-out space and if possible these spaces should be located closest to any natural areas that may be affected by noise.And finally ear protection should be provided for staff and the audience. And good practice means that it should be signed or mentioned in the brochure.