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Figures 2 and 3 show the different coverage that can be obtained
using different installation patterns and a larger number of speaker
units.
For simplicity’s sake, we may assume that the angle of dispersion of
ceiling-mounted speaker units is 90° (tan=1) and that the average
listening height for people is 1.5 m. Thus, in a room with a working
height of
4 metres
a single speaker unit will cover approximately
25/30 m
2
. Generally speaking, it is advisable to avoid installing the
speaker units near corners, as this would lead to an intensification of
the lower frequencies, an effect that is often detrimental for intelligi-
bility. It is also obvious that the height of the ceiling affects the output
power and the number of speaker units to be installed:
High ceiling: more power and less loudspeakers
Low ceiling: less power and more loudspeakers
Wall-mounted speaker units
If the space of the room is such that it is not possible to install ceiling-
mounted speaker units, or it is decided to opt for wall-mounted in-
stallation, there are a few rules to be complied with in order achieve
optimum quality of the sound. With this type of installation, the listener
may be at a greater than critical distance from the speaker unit, with
consequent deterioration of the intelligibility and quality of the sound.
The size of the room, in particular its length and width, are of funda-
mental importance. In order to achieve good results, it is advisable
to use this type of installation only in areas in which one of the lay-
out dimensions measures less than 12 metres, otherwise the sound
pressure will not be uniformly distributed, wherever the wall-mounted
sources are positioned. If the smallest layout dimension of the room is
not greater than 6 or 7 metres, good results are obtained by installing
the speaker units along one of the longer sides, at a height somewhere
between 1.8 and 2 metres. For an optimum distribution, the distance
between any two adjacent speaker units may vary between 5 and 6
metres (Fig.4).
Fig.2
Fig.3
Fig.2
Fig.3
Fig.4
Fig.5
Fig.4
Fig.5
When the shortest side is between 6 and 12 metres, it is advisable to
install the speaker units along both longer sides, alternating them. In
this case the recommended distance between adjacent speakers can
even be doubled (Fig.5). In even larger rooms it will be necessary to in-
stall the loudspeakers in clusters on the load-bearing pillars inside the
room. If there are none, it will be absolutely necessary to use sound
ceiling or speakers hanging from the ceiling.
In the range of speaker units for wall mounting, special attention
should be paid to sound columns, which feature a very narrow vertical
dispersion, ideal for rooms with very high ceilings (domes) with a lot
of reverberation (churches, large workshops, etc.). For optimum distri-
bution of the units, apply the following rules: installation at a height of
about 1.5 metres above floor level if the listeners are seated, or 1.70
metres if they are standing, possibly tilting the sound columns by a few
degrees in the direction of the audience.
Sound-broadcasting along corridors and pathways
Generally speaking, sound-broadcasting in this type of environment is
achieved by means of loudspeakers (sound projectors or horns) instal-
led at regular distances from one another and turned in the same di-
rection, whether in corridors or along outdoor paths (Fig. 6). They must
be connected to one another observing their phases and positioned at
a maximum distance of 15 metres from one another otherwise, in ad-
dition to the sound coming from the speaker unit closest to them, liste-
ners moving along the line formed by the speakers will also hear the
sound coming from the previous loudspeaker, with a delay in excess
of 50 m/sec. This delay will cause deterioration of the intelligibility of
the message being broadcast. An alternative to this type of installation
consists of the use of “two-way” units pointing in both directions along
the corridor. They may be either ceiling-mounted or wall-mounted, and
the distance between one unit and the next should not exceed 30 me-
tres, again so as to avoid the occurrence of reverberation or echoes.
It is possible, of course, to use horn or other types of loudspeaker in
pairs, installing each pair on a single support and pointing them in
opposite directions. The distance between them is the usual 30 me-
tres max. It should be remembered, in any case, that the best results
are achieved using loudspeakers close to one another and featuring a
lower output power. This applies above all to indoor applications.
Fig.6
Fig. 4
Fig. 5
Fig. 6
Fig. 2
Fig. 3