Sound System Design 1333simulates the normal usage of the office area). Measure
the talker’s voices and have them talk louder or quieter
until the talker level is about 60–65 dBA. Adjust the
masking sound level until the listener agrees that the
speech from the talker is audible but not intelligible.
Repeat the process for the other two listeners. The final
system level should be the highest of the three levels.
This minimal privacy level should not be exceeded if at
all possible.
34.6.6.11 Conclusion
Sound masking, speech-privacy systems are related to
other sound systems only in the fact that they use many
of the same components. Their purposes and design are
obviously very different from each other. Masking sys-
tems are commonly specified for public buildings. Such
specifications are drawn up in great detail and require-
ments for installation and performance documentation
are strict. When a design must be performed from
scratch, the help of an experienced consultant will be
valuable.
34.7 Computers and Software for Sound Rein-
forcement Systems
Computers and software programs impact the audio
world in several distinct areas as briefly discussed here.
For additional details, see Chapters 31—DSP Technol-
ogy, 14—Transmission Techniques: Wire and Cable,
15—Transmission Techniques:Fiber Optics, 25— Con-
soles, 29—MIDI, 38—Virtual Systems, 9—Modeling
and Auralization, and 46—Audio Measurements.
34.7.1 Digital Audio Devices
Eventually, most audio products will be based on digital
technology. DSP signal-processing systems, as dis-
cussed in Section 34.4.5, have already become main-
stream products that are extremely useful to the sound
system designer. Several manufacturers are now offer-
ing fully digital audio mixing consoles. Even analog
mixing consoles enjoy important digital features includ-
ing mute groups and VCA groups.
34.7.2 Audio Signal Transmission via Computer
Networks
Cobranet™, developed by Peak Audio, allows transmis-
sion of multiple audio signals over a conventional ether-
net computer network. Other proprietary digital audio
transmission systems are available. Eventually, standards
of this type will enable audio signals to remain in digital
form from the microphone element to the amplifier input
and possibly even to the loudspeaker voice coil.34.7.3 System Control and Monitoring by
ComputerSafety regulations may require that paging systems used
for life safety purposes, such as emergency evacuation,
be supervised. This usually means a computerized
means of monitoring the impedance of the loudspeaker
line. If the impedance changes more than a specified
amount the computer assumes there is a loudspeaker
failure or line short and it signals trouble on the line.
Non-life-safety sound systems may not require
computer control and, in many cases, would not benefit
from it. Larger, more complex systems, however, can
benefit greatly from a central computer set up to
monitor and control the system.
Consider a large airport paging system. Paging
messages originate in individual gate areas, baggage
claim areas, a central paging room, one or more security
areas, and even from outside the buildings. Listeners are
located in many different areas as well.
Paging messages range from “Mr. Smith, meet your
party at Baggage Claim Area 2.” to gate change
announcements, flight change announcements, and
emergency announcements.
Each message must be routed to the appropriate
areas in the appropriate terminals. A priority system
must be established for two or more messages that orig-
inate at approximately the same time. Emergency
priority must be given when needed. In addition, the
system equipment may be widely dispersed and must be
monitored for possible failures. A computerized system,
like that shown in Fig. 34-92, can perform all of these
functions and more.34.7.4 Computer Aided System DesignAs discussed in Section 34.3.2.9.2, software programs
like EASE and Modeler are extremely valuable system
design aids. Less complex software, such as the spread-
sheets offered by Syn-Aud-Con can also aid the system
designer. Other software, such as Stardraw, helps the
designer perform system layout and documentation.