Bosch PRAESENSA, Installation Manual

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PRAESENSA System composition | en 35
Bosch Security Systems B.V. Installation manual 2019.11 | V1.00 |
5. Based on the loudspeaker load, including margin, at least a certain number of amplifiers
is needed to have enough power available to drive the total load. Because all amplifiers
are 600
W capable, divide the total load by 600 W and round up.
– Example: Cluster A needs 5160 W, so at least 5160/600 = 8.6 amplifiers are needed,
that means at least 9 whole amplifiers.
6. Some large loudspeaker zones may need more than 300 W each. These zones cannot be
connected to the same amplifier because then the total power would become > 600 W.
These zones need at least their own amplifier, although smaller zones may be added to
other channels of that amplifier. Count the number of such large zones.
–
Example: Of the 52 zones in cluster A there are 5 with a load of around 400 W, so at
least 5 amplifiers are needed already for these zones.
7. The required number of amplifiers is now the biggest number that came out of steps 4, 5
and 6. That number represents the deciding factor for this cluster.
–
Example: Based on channel count 7 amplifiers are needed, based on total
loudspeaker load 9 amplifiers are needed and based on large zones at least 5
amplifiers are needed. That means that 9 amplifiers are needed because loudspeaker
load is the deciding factor here.
8. To know what type of amplifiers is needed, it is important to consider the average
number of channels per amplifier that is needed for this cluster. When it is <
4, then the
cluster can use 4‑channel amplifiers all over. When it is > 8, then all amplifiers must be
8‑channel. When it is between 4 and 8 channels per amplifier, a mix of both models is
needed, based on interpolation.
–
Example: Cluster A needs 52 channels for 52 zones and uses at least 9 amplifiers.
This is 52/9 = 5.78 channels per amplifier, which is between 4 and 8. Then the
number of 8-channel amplifiers can be calculated via interpolation: 9x(5.78-4)/4 = 4,
meaning that cluster A needs 4 pieces of PRA-AD608, so the other 9‑4 = 5 amplifiers
can be PRA-AD604.
9. Now the minimum number of amplifiers is known and, if no other requirements exist, this
number is sufficient as a basis for further system design, even without knowing what the
actual load of each zone is. Because of other requirements more amplifiers may be
needed, e.g. when certain groups of zones must be connected to the same amplifier; then
it may not be possible to optimize the load assignment across all amplifiers.
Also when the cluster has many relatively big zones and very few small zones, it may
happen that another amplifier is needed because the remaining power budget of each of
the amplifiers is not enough to accept the load of another big zone, although the sum of
all the remaining budgets of all amplifiers is more than enough for that big zone. It may
help to split up such a zone in smaller sub-zones.