Installation; Determining A Suitable Location; Table 12 Sound Levels Predictions - Federal Signal Corporation Modulator MOD Series Description, Specifications, Installation, And Service Manual

Installation

Installation
Read and adhere to all safety warnings in this manual before installing the
Modulator Series Speaker.

Determining a Suitable Location

The output level of the sirens is capable of causing permanent hearing
damage. To prevent excessive exposure, carefully plan the siren location and
post warnings where excessive levels may be encountered. Refer to OSHA 29
CFR 1910.95 for safe exposure limits.
Do not expose personnel to sound levels above 123 dBC.
Careful consideration of the factors affecting the propagation of sound from the siren
and the response of the human ear to the sound will optimize the ability of the siren
to effectively warn the community. Follow Federal Emergency Management Agency
(FEMA) guidelines when designing the warning system.
The reduction of signal intensity, as the distance from the siren increases and the
minimum desired signal level at the fringe of the area to be covered, are important
considerations when choosing a siren installation site. As the distance from the siren
increases, sound level losses accumulate. These losses are a result of weather conditions,
the terrain, obstructions in the sound path, the pitch of the sound and the height of the
siren.
Optimum sound propagation conditions occur when no obstructions exist in the sound
path, the terrain is hard and flat, and the air is blowing away from the source. Under these
conditions, you can expect a 6 dB loss per distance doubled. A loss per distance doubled
of 10 dB is typically experienced because atmosphere is rarely calm, terrain may not be
flat, and buildings or other obstructions are frequently present in the sound path.
Using a 10 dB per distance doubled loss factor, the following sound levels are predicted
for the sirens in the following table.

Table 12 Sound levels predictions

Distance
100 feet (30.5 m) the sound level is
200 feet (61 m) the sound level is
400 feet (122 m) the sound level is
FEMA studies indicate typical ambient sound levels vary by location as follows:
•
•
•
12
Industrial Areas: 70+ dBC
Urban Areas: 60 dBC
Rural Areas: 50 dBC
Modulator High-Powered Omni Speaker (MOD Series)
MOD6024B
121 dB
111 dB
101 dB