Viking 25AE Design Manual page 4

Ambient Noise Levels
Ambient Noise levels also affect speaker count
and placement. Typical noise levels for different
applications are listed in Figure . If you plan to use
background music in your application, plan to boost
volume at least 5 dB above ambient noise levels.
Voice paging demands at least a 0dB volume
increase above ambient to be intelligible. However,
a 5-0 dB increase provides maximum intelligibility
and highest dynamic range.
Noisy applications demand higher speaker counts
and tighter spacing. For voice paging applications
where background music quality is secondary,
select a speaker that has even coverage in the  to
6kHz range (the kHz region is considered the most
important octave for intelligibility).
Sound Falloff and Dead Zones
All speakers exhibit a fairly predictable pattern of
volume falloff as the listener gets farther from away
from the center axis of the speaker. Figure  shows
the difference in volume between the center axis
and 60° off-axis.
An "on-axis" listener seated 3 feet off the floor
(listening height) will experience a normal volume
drop of 6dB. Sound has to travel farther to reach a
listener at the same listening height but 60° off-center
from the speaker axis. That listener will experience
a 5dB volume falloff—a 9 dB difference. Some
speaker manufacturers advertise a 40° coverage
angle. You can see how the wide variation in volume
levels at 0° would be even more unacceptable at
40°.
Edge-to-edge spacing is the least costly way to
design a paging system because it uses the fewest
speakers. If you plan to use an edge-to-edge layout
based on a 0° coverage angle, it's best to arrange
speakers in the hexagonal pattern shown to the
right. Square patterns result in large "dead" zones
shown by the red diamonds. Hexagonal edge-to-
edge patterns reduce the size of the dead zones, but
cannot eliminate them.
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Figure 1 Typical Ambient Noise Levels in dB
30 Quiet library, soft whisper
40 Quiet office, living room
50 Office with office machine noise
60 Conversation
70 Restaurant, factory assembly
80 Automated factory equipment
90 Shop tools, saws, drills
0° Maximum "Real" Coverage Angle
40° Advertised Coverage Angle
Figure 2 An "on axis" listener seated 3 feet off the floor (listening
height) will experience a normal volume drop of 6dB. Yet sound has
to travel farther to reach a listener at the same listening height but
60° off-center from the speaker axis. That listener will experience a
5dB volume falloff—a 9 dB difference.
Regardless of whether you choose a square or hexagonal
pattern, edge-to-edge spacing results in falloff along the edges.
Square patterns also result in the large dead zones shown in
red. Hexagonal patterns reduce, but do not eliminate these
dead zones.
Listening height
The Rule of Thumb
Model results in edge-
to-edge spacing. The
lighter blue outer edges
represent sound falloff.
VIKING