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Idiomas disponibles
Passive networks are very cost-efficient to build.
They also allow the use of one amplifier to drive all
the components of the speaker system.
However,
they have many disadvantages:
a. Inefficiency: A considerable amount of power
produced
by the amplifier is dissipated (wasted)
through
the passive
crossover
network
before
reaching the speakers.
b. Phase shift: Inductive and capacitive character-
istics of the passive networks introduce phase-shift
and distortion into the signal driving the speakers.
c. Intermodulation
Distortion: As all audio fre-
quencies pass through the same amplifier, sub-
bass can intermodulate mid-bass and midrange
frequencies and "muddy" the sound. Also high fre-
quency square-wave components that result from
clipping low frequencies, can quickly and easily da-
mage the tweeters.
d. Unbalanced sound: Due to the fact that one
amplifier is driving all the speaker components, the
output level of each driver is related to its efficiency
only. Low frequency drivers are generally less effi-
cient than midranges or tweeters.
This causes an
imbalance in the output frequency response that
can only be corrected by experimentation and the
use of power-robbing multi-watt resistors.
e. Non-linear Response: Inductive and capacitive
components react with the non-linear characteris-
tics of a real-life speaker (which has its own induct-
ance and capacitance).
This results in unpredict-
able frequency response deviations in the total sys-
tem response that can be very difficult to pinpoint
and correct.
ACTIVE DIVIDING NETWORKS:
Consist of active components such as op-amps and
transistors. These components accomplish the fil-
tering and signal division
before amplification,
while the signal is still at its pre-amp level. An active
dividing network is inserted before the amplifier(s),
after all the pre-amp
level signal processing
is
done. This allows running separate amplifiers for
each component driver. Therefore, passive filters
between the amp and the speaker components are
no longer necessary. By using separate amplifiers,
the drivers
are completely
isolated from
each
other:
a. The inefficiency problem
of the passive net-
works is eliminated because there are no longer
any additional components (such as inductors, cap-
acitors, or resistors) between the amplifier and the
speaker. This ensures that all the output of the am-
plifier is delivered to the speaker.
SIGNAL
PROCESSOR
Pre-Amp
Level Output
ACTIVE
DIVIDING
NETWORK
Pre-Amp
Level Outputs
Speaker
Level Outputs
SPEAKERS
b. Noinductors and only a few small capacitors are
used in active dividing networks. Therefore, large
phase shifts and their associated problems are eli-
minated.
c. Different components of the speaker system are
driven by separate amplifiers. These amplifiers act
as isolators and prevent any interaction and inter-
modulation between the different drivers. Twee-
ters will be safe from high frequency by-products of
a clipping subwoofer.
d. Level imbalances between different speakers
are overcome very easily by adjusting the output
level control of each band.
Because only the pre-
amp input level to amplifier is changed, there is no
loss in efficiency.
e. Advantages related specifically to the 3681 in-
clude near-zero phase shift due to the use of DSP
implemented filters. This helps avoid acoustic in-
terference. In addition, the 3681 allows adjustment
of the time delay of each channel, making the
acoustic alignment of each driver possible
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