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A C O U S T I C S SYSTEM DESIGN AND THE IMPORTANCE OF
A C O U S T I C S
Will your communication
or emergency notification
system broadcast intelligible
speech messages in addition
to alarm tones?
Will your system include
multiple speaker towers or
a combination of speaker
tower(s) and single speakers?
Do you want to be confident
that employee alarms will
be capable of being
perceived above ambient
noise by all employees?
Do you want to save money
on installation costs?
Wouldnt it be reassuring to
know that acoustical experts
with over 50 years
experience are available to
perform an Acoustic Survey
of your facility?
While designing a communication or emergency notification
system, it is critical to consider the acoustic characteristics of
your facility and define these factors as they relate to the
requirements of the communication or alarm system. This
brochure contains information explaining some of the
important acoustic considerations. GAI-Tronics is pleased to
provide this information to help you make an informed
decision when choosing and designing communication systems.
A professional acoustic survey will ensure the intelligibility of
voice alarm messages and increase recognition of tone signals
for all personnel. After all, hearing the message is the whole rea-
son for having a communication and notification system, isnt
it?
Issues specific to industrial environments should be reviewed
and addressed prior to the alarm systems design phase. By
identifying acoustic obstructions and challenges during an
Acoustic Survey, the system can be designed to eliminate or
reduce these effects.
An Acoustic Survey will help define the type of system
necessary to meet your communication needs. When designing
a communication or emergency notification system, you must
consider:
Acoustical phenomena
Facility features - internal and external
Areas requiring coverage
Regional environmental conditions
GAI-TRONICS
®
A Hubbell Company Variables Affecting Acoustics
An Acoustic Survey will determine the most effective way to overcome noisy areas
and provide communication to all employees, despite acoustic phenomena. All of the
following characteristics, individually or combined, will affect the acoustical design.
Multiple Speech Signal Arrival
A critical factor in designing distributed high power cluster systems is maintaining
speech intelligibility when multiple speaker towers are installed. Sound travels at a
specific speed whether the sound is a whisper or a shout. Sounds originating from two
speaker towers at different distances from a given point will be heard at that point at
different times.
If a message arrives at a single point (from two different towers) over a half second
apart and arrives at approximately the same volume (within 6 decibels), the speech
message will be unintelligible.
The effects of multiple speech signal arrival can be greatly reduced by strategically
locating speakers with precise dispersion angles to minimize overlapping of coverage
areas. Pre-recorded voice messages which use a slower speech rate can also reduce the
effects of multiple speech signal arrival.
Acoustical Shadowing
Physical obstructions prevent suitable broadcast levels in the shadow of the obstruction.
If an obstruction is present, the sound level reduction will be significant. The signal loss
is caused by the obstructions partial absorption of the sound.
Areas experiencing acoustical shadowing can be eliminated by repositioning
loudspeakers of adjacent areas to compensate for the shadowing effect. In some
instances, the best solution may be single loudspeakers strategically positioned to
overcome acoustical shadows.
Figure 1. Often the combined effects
of Multiple Speech Signal Arrival and
Acoustical Shadowing make the task
of speaker placement more difficult
than dealing with these problems
individually. It is typical to encounter
both of these factors in industrial
settings.
In Figure 1, the sound level originating
from each tower is equal. The arrival
times are over one half second apart
due to the distance. The volume level
is within six decibels due to acoustical
shadowing from the building. The
result is an unintelligible message. High Noise Areas
Process areas can produce extremely high decibel levels
thus making communication difficult. Figure 2 represents
an acceptable solution because the tower is in the workers
line-of-sight (no obstruction) and the tower is located near
the noise source.
A speech or tone message should be six to 10 decibels
above the prevailing ambient noise. For high noise areas,
similar to Figure 2, it is critical to place the loudspeaker as
close as possible to the sound source. If a loudspeaker is not
mounted close enough to the noise source, the speech will be
too loud in the speakers direct area and not loud enough
near the noise source.
In some cases, it is possible that the sound levels created
by operating machinery will surpass the ability of the
speaker to broadcast an intelligible message as shown in
Figure 3. The signal output level of the tower can be
increased in order to compensate for the noise source;
however, exceeding recommended output levels during
alarm activation could cause hearing damage to personnel.
In addition to the hearing damage, extremely loud broadcasts
are also prone to distortion. Increasing the signal output
level can be an acceptable solution provided the output
level of the tower does not exceed the recommended
decibel limit of 123dB.
Figure 4. Acceptable solution: Tower signaling system
integrated with distributed loudspeaker and/or visual
indicators enhance employee awareness.
Figure 3. Unacceptable solution: Obstructions and noise
producing machinery restrict intelligibility of alarm
messages.
Figure 2. Acceptable solution: Minimal obstructions
exist and tower is located near the noise source. If it is determined by the Acoustical Survey that a tower system is not a viable solution,
a distributed loudspeaker system may be the best solution. A distributed loudspeaker
system provides flexibility when placing the speakers by allowing the loudspeakers to be
located near the noise source as well as in other areas requiring coverage. This solution is
capable of covering all areas where personnel are working. For extremely high noise
areas where personnel are required to wear hearing protection, strobes or other visual
indicators may be necessary as shown in Figure 4. The Acoustic Survey will determine
which of these solutions is right for your facility.
Reverberation
The audibility of tone or speech message can be affected by echoes. Sound reflected
from a surface impairs the listeners ability to comprehend the broadcast. Large open
area, such as warehouses, can be prone to reverberation. One way to minimize the effects
of reverberation is to select loudspeakers with the correct dispersion angles.
Weather Conditions
Because weather conditions, such as wind speed and direction, can contribute to sound
attenuation, it is unrealistic to design a system without considering their impact. For
example, an additional six to eight decibel loss in sound pressure can occur over a
distance of 300 feet with wind speeds of 15 to 20 miles per hour when the wind direction
is from the listener towards the signal source.
Additional variations in sound signal levels due to temperature and humidity can range
from three to 10 decibels per 1,000 feet based on the regional environmental extremes.
We will also review any climate history documented by the facility. An average decibel
loss will be calculated and taken into account when selecting speaker coverage to help
compensate for environment conditions. GAI-Tronics
®
Acoustic Services
Why should GAI-Tronics perform the Acoustic Survey?
With over 50 years of acoustic and speaker layout experience, GAI-Tronics is ideally suited to provide
this service. You will feel confident in knowing that the Acoustic Survey is being completed by someone who
knows communication equipment and is familiar with acoustical architectural layout.
State-of-the-art equipment will be used to identify sound signal levels throughout the facility. Problem areas
will be identified and worst case scenarios will be simulated to ensure that the system will be effective under all
anticipated ambient conditions.
The effectiveness of your system is dependent on the sound quality it produces without intelligible signaling,
the system is rendered useless. An Acoustic Survey will eliminate the guess