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AXIA
Crossover
and Equalization Suggestions
Although available
from the factory in either a bi-amplified or tri-amplified
configuration, AXIA loudspeakers are typically selected for bi-amp use.
The following paragraphs relate to the bi-amplified configuration, which
requires a separate amplifier channel for the LF and MF/HF sections.
Through testing and field experience, suggested crossover and
equalization parameters have been compiled. These should be used only as
a starting point toward reaching the goal of excellent audio
performance. Each specific application will benefit from a carefully
selected configuration.
Crossover:
For optimum performance an asymmetrical crossover configuration is
desired. This should prove simple to implement using virtually any DSP-based
speaker processing system. The processor should be configured for 2-way
operation, providing LF and HF outputs. The processor’s LF output will
connect to the input of the amplifier channel associated with the AXIA’s
LF input. The processor’s HF output will connect to the amplifier
channel associated with the AXIA’s MF/HF input. Configure the LF
output channel’s –6 dB point to be in the range of 170 to 200 Hz. The HF output channel’s –6 dB point should be in the range of 275 to
350 Hz. The slope of both crossover filters should be 24 dB per octave,
with a Linkwitz-Riley filter implementation preferred. The final values
for the low-pass and high-pass filters should be determined after
performing listening, and possibly measurement, tests.
Equalization:
Unless required to deal with room-specific issues, no notch or shelf
filters are typically required to achieve excellent sonic performance.
For additional low-frequency impact a 0.7 octave (Q=1.4) "bass
bump" at 50 Hz can be implemented. Depending on the taste of the
listener, anywhere from +3 to +10 dB of equalization can be very
effective. The test listeners who liked to hear lots of bass energy
selected +10 dB as their preference. No high-frequency horn compensation
("CD horn EQ") is necessary. But adding some if desired will
not cause a problem if carefully selected.
Loudspeaker
Protection:
Implementing a high-pass filter in the LF channel will provide
protection for the AXIA’s 15-inch woofer. This filter will prevent the
woofer from receiving low-frequency energy in the range where it is not
capable of generating significant acoustic output. If not removed by
filtering, essentially all of the energy in this range would be
dissipated in the voice coil as heat. Using a high-pass filter whose
slope is 24 dB per octave, with a –6 dB point at 55 Hz would be
appropriate. If subwoofers are to be used with AXIA loudspeakers,
selecting a higher –6 dB point, such as 80 Hz, will offer additional
protection. It will also allow the subwoofers to perform better in their
intended role.
Practical
Implementation:
In this example, MacPherson loudspeakers were selected to provide
reinforcement for a 300-seat club that specialized in live music. Two
AXIAs, one on each side of the stage, were used in a stereo
configuration. Two SCHOLAR Model 118 subwoofers, arranged in a line
array and driven in mono, provided additional low-frequency
reinforcement. An XTA Electronics DP226 speaker processor was selected.
The DP226’s
subwoofer output was configured to have its high-pass filter –6 dB
point at 35 Hz and its low-pass filter –6 dB point at 80 Hz. The DP226’s
LF output had its high-pass filter –6 dB point configured for 80 Hz. The
LF output’s low-pass filter was set for 198 Hz. The HF output’s
high-pass filter was configured for 321 Hz. The HF output’s low-pass
filter was left in its default setting of 22 kHz. All the filters were
selected for 24 dB per octave, Linkwitz-Riley.
No filters were used
in the DP226’s subwoofer or LF outputs. To account for interaction
between the AXIA cabinets and the club’s physical space, three filters
were used in the HF output channels. The first filter was centered at
606 Hz, had a bandwidth of 0.71 (Q=1.4), and a depth of –2.7 dB. The
second filter had a center frequency of 3.11 kHz, a bandwidth of 0.36
(Q=2.8), and a depth of –1.5 dB. The third filter was centered at
5.88 kHz, had a bandwidth of 0.38 (Q=2.6), and a depth of –3.3 dB.
With the
aforementioned configuration, the overall sonic performance of the
system was excellent. Club management and guests have been uniformly
pleased with the sound.
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