differences between high and low frequency sections. The chief weakness of these systems was their
lack of uniform coverage. System design stressed output conversion efficiency, because of the small
power amplifiers available at the time.
Figure
shows the on- and off-axis curves of a typical horn/reflex system, while polar
response of a typical multicellular horn is shown at B. Note that the off-axis response of the
frequency system falls off considerably at higher frequencies. The typical reverberant room response
of a system composed of these elements is shown at C. Note here the double hump, which indicates
that the total power output of the system is far from uniform. At the same time, however, the on-axis
response of the system may be fairly flat, when measured under non-reflective conditions.
A. Off-axis response of ported horn system
C. Reverberant (power) response of
a
cinema system composed of
elements similar to those shown in Figures 5A and
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3
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Polar characteristics of a 2 x 5 multicellular horn
horn (2 x 5) 1000 Hz vertical
Multicellular horn (2 x 5) 2000 Hz vertical
(so/id); horizontal (dashed)
horizontal (dashed)
Multicellular horn (2 x 5)
vertical
(solid); horizontal (dashed)
Figure 5. Theatre equalization of old-style cinema system
If any attempt is made to equalize the response of this system in the cinema, then the response along
the major axis of the system will be anything but flat. This is precisely the problem which Dolby
Laboratories encountered when they introduced equalization into cinemas during the 1970’s.
