Page 20 - ingenioren

What are the benefits of using higher output To achieve 90dB(A) in an area 50m x 30m
alarm sounders?
In short the use of higher output sounders in
large and / or noisy areas will mean an effective
alarm level giving a robust and unambiguous
alarm dB(A) level. The use of these sounders will
also save considerable installation of cable and
labour.
Consider the following, an area 50m by 30m has
a background noise of 75dB(A) so an alarm level
of 80dB(A) is required. The figure compares one
120dB(A) sounder as equal (actually it would
give a slightly better level) to twelve 100dB(A)
sounders.
To achieve 80dB(A) in an area 50m x 30m
It is obvious which scheme is the most cost
effective to install. It may be interesting to note;
two, 100dB(A) sounders would be adequate if this
was considered as a normal background noise i.e.
to achieve a level of approx 70dB(A).
100dB(A) sounder 120dB(A) sounder
scheme scheme
12 sounders at 1 sounder at 120dB(A)
100dB(A)
Labour for installation Labour for installation of
of 12 sounders 1 sounder
Labour for installation Labour for installation 2
24 cable glands cable glands
Minimum 220 metres Maximum 50 metres of
of cable cable
Labour for installation Labour for installation
200 metres of cable 50 metres of cable
Put your own costs down next to the above and
find out which is most cost effective.
There is no need for calculations to compare the
below. Both schemes will give an alarm level of
90dB(A) i.e the background noise is a maximum
of 85dB(A). In practice the scheme with the two
120dB sounders will give a more effective alarm
level.
• The above assumes all alarm sounders are
synchronised
• Using mid range sounders i.e 105 and 110
dB(A) sounders would require proportionally
more / less sounders
• Diagrams are for indicative purposes, no
allowance has been made for obstacles or
other sound barriers.
• All sites should be subject to a test before
installing alarm sounders.
When should I use mains powered alarm
sounders?
The use of mains powered alarm sounders means
these sounders will have no battery back up. It
is difficult to understand why mains powered
sounders are still considered when 24v dc
sounders are available in versions up to a level
of 140dB(A) with the ability to be powered from
battery back up.
Where should I not use high output alarm
sounders?
High output alarm sounders should not be
used in low ambient back ground noises and
as a means of “drenching” the area in sound.
Alarm systems that are too loud may be
dangerous and cause panic, discomfort and
make communication very difficult resulting
impedance of evacuation procedures. As
guidance, the overall alarm level should be a
maximum of 10 to 15dB(A) over the ambient
background noise.