Two
Unique designs
The architecture of this stadium is particularly striking.
Nestling in the hillside of Monte Castro on the outskirts
of Braga, it is located at one of the highest points in the
city facing the River Cávado valley. This location
was chosen in order to avoid building a dam along the water’s
edge in the valley.
The stadium consists of two stands,
one either side of the pitch, while the hillside forms a
rocky amphitheatre at each end. In addition to the originality
of the contours of this 30,000-seat stadium, there is also
its innovative roof. The roof was originally planned to be
a continuous visor, however, the architect was eventually
inspired by "the suspension
bridges built by the Incas" in Peru, as these allowed
more natural light onto the pitch and would therefore ensure
that the playing surface would be of the highest quality.
In addition to its unique architecture the stadium also has
a unique sound system. The system, specified by Duran Audio’s
Iberian distributor Caius Technologias and installed by Mediachip,
is made up of products from the AXYS Target series. AXYS systems
have, in recent years, become the world leader in providing
highly intelligible speech reinforcement systems within some
of the world’s most acoustically challenging buildings.
The Target system however adds another dimension to the story,
not only can it provide highly intelligible speech reproduction
but Target also offers totally transparent musical reproduction,
even at the high sound pressure levels required in modern stadia.
 Target arrays
The
AXYS Target range is a massive
leap forward in sound system technology. The system has been
designed around Duran Audio’s
scalable array approach. The scalable array approach means that
loudspeakers can be used on their own as a conventional cabinet
(in the case of a Target T2820 with a 90° by 40° dispersion)
or arrayed with other units to make use of the directivity control
that the DDS algorithm provides (An R&D article on DDS,
Digital Directivity Synthesis, will appear soon in A2A). In
order to implement the DDS algorithm each Target loudspeaker
has integral amplifiers, DSP processing and RISC processor.
This makes Target not just a powerful electro-acoustical tool
but also a powerful system integration tool as each unit has
integral delay and EQ capability and the system can be fully
monitored via the RS-485 network.
Design Criteria
The specification of for the stadium stated that the sound
system should meet the performance specification:
• The system should be capable of delivering an average
A-weighted SPL of 100 dB(A) with a maximum deviation ± 3
dB(A) for 90% of the audience area.
• The frequency range should be 50 Hz-18 kHz.
• The STI (Speech Transmission Index) should be larger than 0.45. This
means that the speech intelligibility should be ‘Fair’ or better.
The Solution
In order to meet the performance specification criteria Duran
Audio in cooperation with Caius Technologias and Mediachip
produced the following design using products from the AXYS
Target range.
Fig 1: Schematic overview
of the geometry of the stadium and the mounting positions of
the four Target clusters and six U-16 loudspeakers on one side
of the stadium. The other side is identically equipped.
Each stand at Braga has 4 cluster locations.
At each location there is an array consisting of two Target
B-215’s (Bass),
and two Target T-2880’s (Mid-Hi). These clusters are
designed to cover both the upper and lower seating decks. Thanks
to Duran Audio’s unique DDS technology the vertical directivity
pattern of these arrays can be manipulated, using Duran’s
DDA software. This meant that the arrays could have a directivity
pattern that was tailor-made to meet the geometry of the Braga
Stadium.
However, it was found that there would be a significant shadowing
at the rear of the lower deck, caused by the overhanging upper
deck. To ensure that the performance criteria Stadium was met
in these areas eight Target U16 loudspeakers were used as fills.
Like the larger Target unit’s the U-16 has integral amplifiers
and DSP processing and is designed as a scalable array system.
The scalable array approach means that loudspeakers can be
used on their own as a conventional cabinet (in the case of
the U-16 with a 90° by 90° dispersion) or arrayed with
other units to make use of the directivity control that the
DDS algorithm provides.
The Result
Once the system had been installed representatives from Duran
Audio helped commission the system and it was found that the
system not only met but exceeded the performance specification.
Sound level distribution (LA)
The measured sound level (i.e., A-weighted SPL) values at
the upper and the lower deck are shown in Fig 2. The mean sound
level during the measurements was 101.2 dB(A). At this level
a headroom of 6-8 dB(A) is left in the system.
Fig 2: Plan view of the upper and the lower
deck on one side of the stadium with the measured sound levels
(LA).
STI distribution
The measured STI values at the upper and the lower deck are
shown in Fig 3. The mean STI value is 0.54.
Fig 3: Plan view of the upper and the lower
deck on one side of the stadium with the measured STI values.
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