Handbook for Sound Engineers

Sound System Design 1331

baffles are available to help diffuse the masking sound,
and several manufacturers produce special loud-
speaker-enclosure combinations designed specifically
for sound-masking to allow the upward or sideways fac-
ing orientation.

34.6.6.5 Criteria for the Amplification System

A standard pink-noise generator, of the type used for
sound system equalization, is acceptable provided its
output is random enough. Many equalization noise gen-
erators utilize digital circuitry, with only pseudorandom
noise. Listeners may become aware of this type of gen-
erator making it unacceptable. Noise generators specifi-
cally designed for sound masking systems are available
and are worth any extra cost. The noise generator, like
the power amplifier, must be highly reliable. Redun-
dancy can be achieved by mixing two noise generators
through a passive mixing network. If one generator
fails, the overall noise level will drop about 3 dB, but
the system will continue to operate.

34.6.6.6 Criteria for the Equalizer

Because the shape of the final frequency-response curve
is critical, and standard masking system curves are
specified in -octave intervals, a -octave equalizer
should be employed. If two, redundant, active equaliz-
ers are used, the filter and gain settings on both must be
exactly equal.

34.6.6.7 A Second System

A more random (and thus more effective) system design
can be achieved by utilizing two separate noise genera-
tors feeding two equalizers and two power amplifiers
(or banks of power amplifiers in a large system) as
shown in Fig. 34-90. Rather than feeding zones of loud-
speakers in separate areas, these amplifiers feed adja-
cent loudspeakers in the same zone in a checkerboard
pattern. This plan also produces a higher level of redun-
dancy since failure of one amplifier or noise generator
will produce only a 3 dB drop in overall masking level.
Thus, this system can be installed with no backup
amplifiers if desired. Alternately, a single backup ampli-
fier can be installed in the system rack, ready to replace
any single amplifier failure.

34.6.6.8 Masking Plus Paging or Background Music

Background music or paging may be added to a mask-

ing system using the same amplifiers and loudspeakers.

Intelligibility of the paging may suffer because of the

placement of the loudspeakers. (High frequencies will

be attenuated.) A separate equalizer should be used for

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Figure 34-89. Sound masking loudspeaker shown in three
hanging orientations. Courtesy Atlas Sound.
C. Upwards.
A. Sideways.
B. Downwards.