Treasurer Ingemar Ohlsson (left) and Secretary Steven Liddle (right) at the March 20 2014 Swedish Section meeting.
The March Section meeting was held at Sweden's National Football Arena, Friends Arena, Solna. AES members Lennart Nilsson, Ingemar Ohlsson (Treasurer) and Steven Liddle (secretary) all had their part to play in the acoustic and electroacoustic design of the arena and its systems.
Lennart began proceedings with a talk that detailed all of the acoustical aspects that were considered during the course of the build. With the arena having to perform a variety of functions the acoustics of the bowl were designed to reduce reflections and reverberation as much as possible. With the roof being closeable it was important to ensure that the acoustics were similar regardless of its position. The moving section is basically a giant porous absorber with 80mm mineral wool held in place behind wire netting. This means that the roof behaves a lot like an open window with very little energy returning to the bowl. The remainder of the roof is perforated panel backed with porous absorber with the aim of providing as much practical low frequency absorption as possible. Other features included custom designed gigantic attenuators on the roof based ventilation systems to prevent concert audio and crowd noise leaking out to the surrounding residential areas. Seating was chosen so that empty seats flipped to an upright position thus reflecting acoustic energy towards the roof.
Ingemar and Steven then described the design criteria for a flexible, modern and resilient combined voice alarm and public address system. Electroacoustic modelling was carried out during the consultation stages in order to establish system designs that would cover 50,000 seats and 15,000 people standing on the field of play during concerts. Two design philosophies were considered — line array and point source. 12 line arrays or 30 point source clusters would adequately provide foreground music and commentary for sporting events, support for concerts as well as intelligible reproduction of speech for emergency announcements.
Life safety played a primary role in audio distribution design with dual, redundantly configured networked audio systems being the preferred solution. Maintained power supplies were provided from the arenas central power systems where two mains feeds are taken from independent, geographically located supplies. Diesel generators are also in place which can be used as supplies for essential services or handle switch over to large battery backups.
Members and guests were then invited out into the arena to audition a sample of speech and music.
