JBL CINEMA SOUND SET UP, Руководство пользователя

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In mid-size screening rooms there is less air loss to deal with, and it is often the case that no
more than a
1
boost is required to meet the equalization requirements above 10 Many
conservative engineers feel that a boost should never be exceeded.
Use of Multiple High Frequency Elements
In some very large old-style houses with balconies, a nominal high frequency coverage angle
of is not sufficient to provide vertical coverage. Some systems have been installed with multiple
high-frequency horns to take care of this problem, but the difficulty of interference, or ‘lobing,’ in the
combining of the two horns remains, creating difficulties in system equalization. There are experiments
under way to use stereo synthesizers as a method of alleviating gross effects of interference, but
these experiments are only in the beginning stage (8). For the present, we do not recommend that
horn stacking be applied in the cinema -- unless it is specified by a competent consultant who will take
responsibility for overall system performance.
V. MOUNTING REQUIREMENTS
A. General Comments
The following rules generally to screen loudspeakers:
1.
2.
3.
4.
5.
They should be located vertically so that the horns are between one-half and two-thirds the
height of the screen.
They should be placed so that the horn flanges are within a distance of 5 to 7 cm (2 to 3 in)
of the screen.
All reflective details, such as logos and polished frames, should be painted matte black so
that they will not show through the screen.
Platforms for loudspeaker mounting should be rigid and completely free from rattles; all
exposed vertical surfaces should be finished with sound absorptive materials.
All other wall areas behind the screen should be finished with sound absorptive materials.
B. Platform and Baffle Construction
If a THX system is specified, all details of the vertical baffle 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. Figure 25 shows a detail of a platform for behind-screen use. The
loudspeakers should be mounted on sections of carpet, or some other such material, to inhibit rattles.
Enclosures should be secured with angle brackets so that they have no tendency to move.