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Public address systems are used for voice, music and alarm Loudspeakers with different power ratings can be jointly used
transmission. To this end, the useful signal is modulated onto a in a line or group. The minimum power of the amplifier is the
carrier voltage (50 V, 70 V, 100 V) and reaches the loudspeaker sum of the individual loudspeaker power ratings in the pub-
via a transmitter. This transmitter transforms the low imped- lic address system. When determining the minimum power of
ance of the loudspeaker to a higher value, thus reducing the the amplifier, the sum of the loudspeaker power ratings is not
current. Therefore, telecommunication lines with a diameter of decisive, but instead the sum of the selected power ratings at
0.6 mm or 0.8 mm can be used. the transmitters.

There are different kinds of loudspeakers. Flush and wall loud- Subsection 7.2.1 of the EN 50174-2 standard describes the pro-
speakers typically have a rated power between 6 and 30 W, tection from lightning strikes and induced surges and compares
column loudspeakers between 20 W and 100 W and horn loud- the risk of damage with the risk which is accepted by the oper-
speakers between 10 W and 60 W. Modular amplifiers have a ator. If this risk assessment reveals that surge protection meas-
rated power between 100 W and 600 W (in some cases even ures are required, surge protective devices must be installed
higher). for the relevant installations and systems in need of protection.

100 V loudspeaker
MEB
power amplifier 100 V relay module
100 V loudspeaker
MEB
DCF 77 antenna
CD player
MEB

230 V system
RS 232
tuner
MEB

intercom with
function and
MEB selector buttons
central unit 230 V system
with input slots
MEB

75 Ω coaxial cable

No. Surge protective device Part No. No. Surge protective device Part No.
DR M 2P 150 (current > 1 A – 25 A) or 953 204 BXT ML2 BD HFS 5 920 271
+ BXT BAS 920 300
BXT ML4 BE 180 (current < 1 A) 920 327
+ BXT BAS 920 300 DR M 2 P 255 953 200
DGA G BNC 929 042 DGA FF TV 909 703

FS 9E HS 12 924 019 DPRO 230 909 230
Figure 9.8.1 Modular public address system with surge protective devices

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