Fitness studio, North West

The challenge

A coach who ran small fitness classes took on an empty railway arch and applied to change its use. The council sent the application straight back as invalid. Before it would even be considered, it wanted a full acoustic study and a scheme of soundproofing works: draught lobbies at the doors, treatment to the structure, a sound limiter wired into the music system, acoustic glazing and treated ventilation. A block of new flats was going up directly opposite, about thirty metres away.

For classes of around ten people in a leased arch, that package of works would have taken a serious bite out of the fit-out budget, and possibly out of the business case. The council's noise limit is also a demanding one, judged on the assumption that the neighbours' windows are open, and it bites hardest on bass, the part of music that travels furthest and is hardest to contain. The first class of the day starts at six in the morning, which falls inside the council's night-time hours, so the quietest part of the day had to be assessed too.

What we did

We monitored continuously for three days, covering weekday daytimes, the weekend and the early-morning hours before seven. That established how quiet the surroundings actually get, which is what the limit is set against.

The important step was refusing to assume how much sound the arch held in. Rather than take a figure from a table, we measured it: test noise was played inside the unit and recorded outside, which gave the real performance of the structure the operator already had. We then measured a genuine class, using the operator's own stereo at the level their normal routine uses, during the loudest part of the workout.

That gave two real numbers instead of two estimates: what the class actually produces, and how much of it the building actually stops. The rest is arithmetic across to the flats opposite.