Specifications

TI 323 (6.0E)
12 - 36
STI (Speech Transmission Index) of 90°x50°, 60°x40° and
35°x35° system
Sound pressure coverage of 90°x50°, 60°x40° and
35°x35° system
Comparison of a single 90° coverage cabinet with
a 3-wide array of 35° systems
90
35
35
35
-45 0 +45
-6 dB
-6 dB
diffuse sound
-45 0 +45
One can easily see, that the narrow dispersion
cabinets give greater throw and higher levels towards
the far field, but are compromised by uneven near
field coverage.
Speech intelligibility is also influenced by the
variations in loudspeaker coverage. The second
illustration is a plot of the Speech Transmission Index
(STI) over the listening area used in the previous
illustrations. There are very clear differences in speech
intelligibility; white and light grey show the areas of
high intelligibility. As the coverage of the
loudspeakers narrows, speech intelligibility quite
clearly improves in the far field.
4.4. Speaker placement considerations
4.4.1. Vertical coverage
The vertical aiming of a cabinet, the height and the
angle, largely determines the sound level distribution
from the source to the back of the room. To achieve the
best coverage requires that the speaker height and angle
are set independently. Placing the loudspeakers too low
and too close to an audience will give high level near
field at the expense of inadequate far field coverage.
Higher speaker placement will produce more even
audience coverage from the front of the stage to the
back of the room.
Particularly in smaller venues, a speaker placed too high
directs too much energy towards the back of the room
where it can reflect off the rear wall. This will create a
diffuse sound and ruin intelligibility by reducing the ratio
of direct to reflected energy. It may also generate a very
audible 'slap' echo. Simply tilting the speakers down and
aiming them towards the audience can prevent these
effects.
4.4.2. Horizontal coverage
The horizontal coverage angle of the loudspeakers
should not be wider than is necessary to cover the
audience area. Sound radiated in other directions
adds energy into the diffuse sound field, which will
decrease intelligibility.
The angled rear side panels (15°/C4/C3 and 25°/
C7-TOP) indicate the horizontal arraying angle of the
loudspeaker. Using these angles it is possible to verify
the nominal horizontal coverage visually from behind
the cabinet.
If a single system does not provide enough coverage,
more cabinets can be put together in an array. This
requires that systems have good constant directivity
characteristics in order to keep the overlap regions as
small as possible and also not leave any coverage
gaps.
4.4.3. Coupling of multiple systems
If, for example, a horizontal coverage of 90° is required,
it can be achieved with a single 90° system, or with three
35° degree systems with a 30° angle between each
cabinet. The latter solution clearly gives more sound
pressure and a much sharper level drop at the edges of
the coverage area. The sharp level drop at the edges is
a very valuable effect when working in highly
reverberant environments, since the amount of energy
wasted into the diffuse field is dramatically reduced.
Excellent constant directivity properties of a single system
are essential to enable the creation of array solutions.
When arraying C3 or C4-TOP systems at 30°/ C7-TOPs
at 50°, an extremely smooth overlap with minimal
interference is ensured (see isobar plots in chapter 1).