A neighbour hears aim and level, not the rating of a wall that is not there.

Outside

Environmental noise rules set a limit at a dwelling façade or during the night, and they differ from one city to the next. They are not replaced by Rw. The designer’s tools: aim the horns away from housing, hang height, directivity, and an agreed operating level. A stand or a wall shades sound in one direction without deleting it. A promise that ‘the stadium is insulated from the neighbourhood’, in one sentence, is a false promise. The line is written: a level at the receiver, at the agreed hour, with the system running at the agreed setting.

A partial roof, and a closed arena

A roof over part of the bowl returns crowd and horn energy to the seats and lengthens the tail. That is shape, and absorption on the underside if it is needed, not insulation. A fully enclosed arena gains a shell to the street: walls, gate doors, and silencers on air intakes. Here DnT,w between the hall and outside returns, together with an environmental limit at the neighbour. Mixing the two types in the same schedule is the cause of most disputes after the first match.

• Audience gates left open at peak time cancel façade insulation. Say so in the operations note.
• The emergency generator on match night is a neighbourhood line of its own, separate from a silent test day.