Page 19 - ingenioren

More tips: In the open a sounder will spread in
all directions, but in an enclosed space some
of the sound will be reflected and an increased
sound level will result. b) If the alarm sounder,
already mounted on a wall, is positioned near
to a ceiling, more sound will be reflected. Vice-
versa for a ceiling mounted sounder. c) An alarm
sounder mounted on a wall is more effective than
when mounted on a pillar. d) Sounders should
be sited so as to avoid immediate obstacles and
at an ideal height of approx. 2 to 2.5 metres. e)
Sounders when installed that are synchronised
will give a more effective overall effect.
How many alarm sounders do I need?
When the area to be covered is large and / or
noisy, many designers feel unsure and or / go
for the ‘add-lots-more-bells / 100 dB sounders-
than-normal-approach’. This usually leads to
an inadequate coverage and / or the addition of
sounders to achieve the bare minimum alarm
level after the system has been evaluated during
commissioning along with the costly addition of
more cable, terminations and labour.

If a room with an area to be covered with an
audible alarm is say 30 metres by 20 metres
large with very little background noise (approx.
65dB(A)) then it would be reasonable to assume a
100dB sounder would cover this area as it has a
70dB(A) range of approximately 30 metres in low
ambient background i.e. giving 5 dB(A) over the
background noise (please see later).
Question: how many sounders would you require
if the background noise were 85dB(A) say in a
heavy machine shop?
Answer: One! The background noise has
increased by 20dB(A) then install a sounder
20dB(A) louder i.e. a sounder rated at 120dB(A).
Common sense! This principle may be used in all
applications where noise and large areas are to
be covered.