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select the appropriate configuration. This configuration
can include equalization but it can also include mixing
and output signal routing.
Second, DSP allows multiple signal-processing
devices at reduced cost. This opens up opportunities
that were previously available only in high-cost
systems. For example, consider a religious facility with
distributed column loudspeakers mounted on pillars
down each side of the main auditorium. DSP can
provide separate delay for each pair of loudspeakers,
and it can even provide separate equalization. This can
be valuable when the first pair is near the platform, the
last pair is near a balcony, and the others are in yet a
different acoustical environment.
34.4.6 Digital Audio Networking
More and more audio processing is done in the digital
domain. Thus, it seems natural that audio signals should
be transferred between devices in digital form. In some
cases, this is a simple matter of connecting the digital
output of one device to the digital input of another
device. Audio devices with AES/EBU inputs and out-
puts are set up for this kind of connection.
In some systems, it may be useful to route multiple
channels of audio from one location to another. For
example in a performing arts center, it’s commonly
necessary to transfer multiple channels of audio from
the stage to the mixing location and from there to the
system rack room. If most processing is done in the
digital domain it makes sense to keep the signals in
digital form during these routing functions.
Although proprietary systems exist, most digital
audio networking systems are based on Ethernet
computer standards. The best known of these is
CobraNet, developed by Peak Audio, a division of
Cirrus Logic. CobraNet is licensed to a number of other
manufacturers who have incorporated it into their
products.
CobraNet and other digital audio networking
systems enable multichannel digital audio transmission
over CAT5 or fiber optic lines. They may also enable
channel routing and patching functions, a sort of digital
patch bay. Also, these transmission systems often
include channels for system control signals and system
monitoring information.
See Chapter 39 for a detailed discussion of digital
audio networking.34.4.7 Power AmplifiersPower amplifiers for sound reinforcement should con-
form to the general specifications presented in Section
34.4.1. In addition, they must be able to drive profes-
sional loudspeaker loads and long loudspeaker lines.
For this reason, a typical home entertainment power
amplifier, while it may be a very high-quality product,
is not suitable for professional or commercial usage,
Figs. 24-50.Most professional power amplifiers are two-channel,
or multichannel solid state, analog devices with rack
ears and cooling fans. Some include 70 V output trans-
formers for use with distributed systems. Some have
optional DSP modules as described in Section 34.4.5.
Some have switching power suppliers to reduce their
size and weight.
Power amplifiers should include an output relay or
other method of uncoupling the loudspeakers from the
power amplifier during turn on and turn off to avoid
turn-on/turn-off transients from mixers and signal-
processing devices. Also, the output relay disconnects
the loudpeakers in the event of amplifier failure.
Some manufacturers offer multichannel power
amplifiers with several power amplifiers in one chassis,
Fig. 34-51. These power amplifiers can often be
combined to form higher-power amplifiers or 70 V
outputs. For multichannel systems, this type of power
amplifier can often reduce costs.Figure 34-49. Loudspeaker DSP processor. Courtesy BSS.Figure 34-50. A two-channel professional power amplifier.
Courtesy Crown International.Figure 34-51. A multi-channel professional power amplifier.
Courtesy QSC.