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B. Screen Loudspeaker Aiming:
If a THX
system is specified, all details of the vertical baffle wall (or bafflette construction) will be taken
®
care of. Where there is no such specification, the installer will have to construct one large platform, or a number of
smaller ones, depending on costs. The loudspeakers should be mounted on sections of carpet or rubber pads to
inhibit rattles. Enclosures should be secured with angle brackets so that they have no tendency to move. All wall
surfaces behind the screen should be finished with sound absorptive material.
The screen loudspeakers should be spaced laterally so that good stereo imaging is ensured. The screen
loudspeakers should be oriented so that they point to a location on the centerline of the house at a distance
about two-thirds the length of the house. This will require that the left and right screen loudspeakers be toed in
regardless of screen curvature. This will ensure that proper stereo imaging will be perceived by those patrons
seated toward the sides of the house. Normally, if a curved screen is used, its radius of curvature will be struck
from a center point in the room that is about two-thirds the depth of the room. Overall details here are shown in
Figures 28 and 29.
The HF and MF horns should be given a downward elevation angle so that they are aimed at the
audience ear plane at the point two-thirds back in the house, as shown in Figure 30.
Figures 28: Toeing in of screen loud-
speakers behind a flat screen.
Taking into account the requirements for masking for various aspect ratios, the spacing between left and
right loudspeakers should be broad enough to produce ideal stereo for the widest format. Acoustically transparent
masking material should be used so that, when masking is in place, there is negligible high frequency loss. The
wider loudspeaker spacing, when used for a narrower projection format, will be quite acceptable, even desirable.
C. Subwoofer Mounting:
For best results, the subwoofers should be placed on the floor below the screen loudspeakers and,
if possible, against a vertical wall or baffle. They should be clustered together resting on rubber pads and be
completely free of rattles.
D . Surround Mounting:
With traditional digital sound tracks there are two surround channels. Figure 31A shows a plan view of
how a total of 12 surround loudspeakers would be divided into two channels. Normally, the surround loudspeakers
are carried no farther forward in the house than a point about one-third the distance from the screen to the back
of the space. The reason is simply that the surrounds should never be perceived as competing with the screen
channels. Figure 31B shows a section view of the house looking toward the screen. JBL surround loudspeakers
include an integral 20° downward tilt for ease in proper aiming. Generally, the surrounds should be placed 3 to 4.5
meters (10 to 15 ft) above the floor and aimed roughly at the wall/floor boundary on the far side of the space.
22
Figures 29: Screen loudspeakers
normal to a curved screen.
Figures 30: Downward elevation of
screen loudspeakers.
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