 Belgium's
capital Brussels is home to the European Parliament and many
other European Union institutions and organisations. Most of
the 20 million passengers that pass through Brussels airport
each year are business travellers, the vast majority travelling
on EU related business. Pier A now handles over fifty percent
of Brussels entire traffic. In addition to the new concourse
a connecting building - the Topaz - has been constructed, linked
to the terminal by a 250-meter long tunnel under the apron.
Pier A was officially opened on May 15th, 2002. The architecture
of this pier is special in several ways. Firstly, the design
has been highly influenced by the reading of the airport’s
radar and instrument landing (ILS) system. It was necessary
to give the building a round edge on the north side and an
inclined straight edge on the south side, to minimise distortions
and interference patterns. This led to the overall shape of
the building, which is reminiscent of an aeroplane wing and
gives it a sense of movement.
A second, and quite spectacular feature of
the new pier is the absence of any conventional supporting
columns in the passenger area. This has been made possible
by an aluminium roof skin supported by 68 3D-profiled steel
beams. On this project there was a requirement to have a reduction
rate of 53 dB(A) on any sound passing through the roof so a
new composite material had to be conceived especially for the
project. A third feature, also conceived for this project,
are the fully transparent, allglass facades. They are cantilevered
to add to the effect of volatility and they provide passengers
with a grandstand view of takeoffs and landings on the runway
that runs parallel to Pier A at a distance of just 400 m. The
imposed acoustical transmission reduction of 43 dB(A) is realized
by a laminated glass panelling construction.
 |
| Fig.1 Model used for acoustical
simulations |
Electro-acoustic
consultant Cees Mulder of Dutch company LBP designed the sound
system, in cooperation with Duran Audio's Evert Start, who
carried out the CATT simulations. Mulder was first contacted
for the project in December 1999 by Jean-Marie Malchair of
Tyco Belgium. At the time Mulder was working on the sound system
for Dubai International Airport, which was near completion
and happened to be quite similar to Pier A: a very long pier
with gates on either side. “Since
the system worked so well in Dubai, it made a lot of sense
to use the same concept for Brussels,” he says. Basically
the design consists of a series of Intellivox-4c columns (now
known as the DC 430) used in pairs, mounted on either side
of the pier. Each pair, Mulder explains, covers an area of
approximately 60 m deep and 38 m wide, which holds four gates.
At the end of such an area the pier slightly narrows, working
like an acoustic silencer. To compensate for this effect a
pair of 2b’s (DC 180) are used
in these narrower areas to augment the 4c’s (DC 430),
filling in until the pier widens again into the next gate area
where the next 4c’s (DC 430) take over. This
pattern is repeated over the full 650 m.
 |
| Fig.2 Simlations of SPL (left) and RASTI (right) |
The vertical opening angle of the individual
4c (DC 430) columns has been set to 60, with the acoustical
mounting height at 2.5 m. All further system adjustments were
based upon MLSSA measurements and extensive listening tests,
in which the overall performance of the system was evaluated.
The system has been set to produce an equivalent sound pressure
level Leq of 64 dB(A) when an automatic message is reproduced.
Automatic gain correction has been implemented with a range
of 6 dB. It is activated whenever a noise level of 58 dB(A)
is exceeded. Measurements carried out at Gate A51/A53, representative
for all other gates, show that the sound level at 1 kHz varies
between 74 dB and 80 dB in the entire area (for sufficient
signal to noise ratio, these measurements were carried out
at a higher level than the normal operating level). As to equalisation,
system response has been smoothed out between 200 Hz and 4
kHz, SPL drops below 200 Hz and above 4 kHz.
 |
Fig.3 Measurement positions 1-17,
Gate A51/A53 (not to scale) |
All Intellivox units are equipped with two
line inputs, enabling separate connection of ‘general’ and ‘local’ audio
feeds. Level dependent input priority switching is implemented
in the DSP software, any local message is overruled by an incoming
general announcement. Furthermore, the predelay can be adjusted
for each input individually. For general (’all-call’)
announcements all units are time-aligned (’point zero’ at
the beginning of the 650 m long pier), for local announcements
the predelay has been set to 0 ms. Due to the late (> 100
ms) arrival of the direct sound at some of the desks used for
the local announcements, the comfort of speaking was expected
to be insufficient without any special precautions. A solution
was found in local monitoring with small conventional loudspeakers
that are installed in the desks. The STI (Speech Transmission
Index) was measured over a distance of 80 m in the area of
Gate 51/Gate 53, and reaches values between 0.50 and 0.66.
According to the STI standard these values represent sufficient
speech intelligibility, for well articulated complicated messages,
to be interpreted by non-trained listeners. The average STI
is 0.57 with a deviation of 0.065. Even the lowest STI value
of 0.45, measured at one single point, still stands for reasonably
good. That the sound system works really well is not only confirmed
by these figures, but also by the airport authorities and passengers,
listening to announcements. In fact they have been giving positive
response very spontaneously. According to Jean-Marie Malchair
the general feeling is “that the quality of the speech
intelligibility is remarkable for this kind of large structure.”
| Position |
Distance (M) |
STI - Walking Area |
STI - Waiting Area |
| 1 |
0 |
0.65 |
- |
| 2/11 |
3.5 |
0.66 |
0.65 |
| 3/12 |
13.1 |
0.63 |
0.57 |
| 4/13 |
22.7 |
0.62 |
0.55 |
| 5/14 |
32.3 |
0.53 |
0.53 |
| 6/15 |
41.9 |
0.50 |
0.55 |
| 7/16 |
51.5 |
0.45 |
0.50 |
| 8/17 |
61.1 |
0.50 |
0.50 |
| 9 |
70.1 |
0.63 |
- |
| 10 |
79.1 |
0.64 |
- |
| Fig.4 Measured STI Values
at Gate A51/53 |
Back
to main Install page | Next
Case Study |
