Bosch PRAESENSA, Руководство по установке

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34 en | System composition PRAESENSA
2019.11 | V1.00 | Installation manual Bosch Security Systems B.V.
Traditionally the power amplifiers also use transformers to convert the relatively low maximum
output voltage of the amplifier to the standardized 100
V distribution level. The size and
weight of these transformers scale with their power handling capabilities and determine to a
large extend the size and weight of the whole amplifier. PRAESENSA amplifiers, however, use
high power supply voltages to create a 100
V (or 70 V) output signal without the use of output
transformers. This does not only saves weight but also improves the audio quality, as
transformers operate within a limited frequency range and may suffer from core saturation at
very low frequencies. Another big benefit is that the output power of an amplifier channel is
not limited anymore by the size of its output transformer, an important pre-condition for
flexible power allocation across output channels for multi-channel amplifiers.
5.2 Amplifier selection
The flexibility of the PRAESENSA multi‑channel power amplifiers makes it possible to cover
most demands with just a few different models, the PRA-AD604 and PRA-AD608. Both models
have a power budget of 600
W in total, to power the loads for 4 or 8 channels. Because the
channels can be loaded with any amount of loudspeaker load within the 600 W budget of the
whole amplifier, only the average channel load determines which amplifier fits best to the
load. The PRA-AD608 is capable to drive 600
W of load into 8 zones, so it fits best when the
average zone size is 600/8 = 75 W, or less. The PRA-AD604 fits best when the average zone
size is 600/4 = 150 W, or more. When the average zone size of a large system is between 75 W
and 150 W, then a mix of PRA-AD604 and PRA-AD608 amplifiers is needed.
To determine quickly the minimum amount and type of amplifiers that are needed for a
project, use the following rules:
1.
Check how many locations are needed for equipment clusters to be installed (technical
rooms). System decentralization into clusters is often needed because of the size of the
area that needs to be covered by the system. Decentralization of equipment is a good
way to minimize the amount of loudspeaker cabling by positioning the amplifiers closer to
the connected loudspeakers in each zone. Often clusters are located per fire zone, each
covering multiple separately addressable smaller zones, to mitigate the requirement of
fire resistant loudspeaker cabling.
–
The next steps for calculation must be executed for each cluster separately.
2. Count the number of zones for this cluster. Zones with a loudspeaker load > 600 W need
to be split into sub-zones with a maximum load < 600 W each, because they require more
than one amplifier. Then count the subzones instead of the original large zone.
–
Example: Cluster A serves 52 (sub-)zones, each needing its own amplifier channel.
3. Add up the loudspeaker loads of all zones to get the total loudspeaker load. For
loudspeakers that are tapped down to get the required sound pressure level (and not
more), use the tapped down power setting in the summation. Often a project asks for a
margin on the power for later expansion, then count that margin in.
–
Example: The total loudspeaker load for cluster A is 4300 W and 20% margin is
needed. Then the total load for calculation is 4300x1.2 = 5160 W.
4. Based on the number of zones at least a certain number of amplifiers is needed to have
enough channels to drive each zone separately. Because the PRA-AD608 has the most
channels (8), divide the number of zones by 8 and round up.
–
Example: Cluster A has 52 zones, so at least 52/8 = 6.5 amplifiers are needed, that
means at least 7 whole amplifiers.