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Environmental sound dispersion
Environmental sound dispersion is most efficiently reduced utilizing a combination
of a sound absorbing platform cover with a reduction of the number of openings
that stand in contact with the surrounding area.
The figures 9 - 10 have already indicated that a soundproofed roof reduces the
sound levels under the cover. The surrounding area enjoys these reductions in a
similar way.
Figure 4.2 shows that the shape of the cover partly “concentrates” the noise in
the separate modules. This also reduces the noise level of the surrounding area.
The surface area of the open entrances on the short side of the cover was kept
relatively small to ensure limited ambient noise bleeding.
Finally, the public address system is designed in such a way that it generates a
clear and sufficiently audible sound volume at the local level of the platforms only.
Special care is taken to avoid amplifying sound over the whole volume underneath
the cover with the public address speaker system.
The future environmental sound levels of the public address system will therefore
be significantly lower than at present.
Selection of the public address (PA) system.
This section investigates how the PA system can deliver passenger announcements
at an optimum speech intelligibility level. The first part briefly considers the
concept of speech intelligibility. The most important parameters that define
speech intelligibility are indicated. The second part presents an analysis of speech
intelligibility levels in the area underneath the cover. The last part addresses the
most important characteristics of the proposed PA system.