Behringer CX3400 - Manual (Page 15)

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3.3.1 Finding „drop-outs“ in the frequency response
Check the entire frequency response of the system. Rooms have quite an impact on the frequency response
of speaker systems, due to resonance and various reflections. So, you cannot expect to achieve a linear
frequency response right from the start. Use an equalizer such as our ULTRA-CURVE PRO DSP8024 or
ULTRA-GRAPH GEQ3102. Look for drop-outs around the crossover frequencies (there should be none, if the
output levels have been set properly, as described in paragraph 3.3)!
However, if the frequency response shows some irregularities, it can prove useful to correct it by means of
the crossover network, before using an equalizer (EQ). Subsequently, the crossover frequencies must be
corrected with an EQ as far as this is possible.
3.4 Setting the crossover frequencies
The use of extremely high-grade potentiometers made it unnecessary to install fixed-frequency plug-in modules.
Thus, you have a wide range of setting options available that even more expensive crossover networks hardly
give you.
The CX3400 works in two specific frequency ranges: 45 though 960 Hz and 450 Hz through 9.6 kHz. The
Linkwitz-Riley filters employed in the SUPER-X PRO feature a slope of 24 dB/octave. High-grade components
such as 1%-tolerance metal-film resistors ensure a perfect phase and amplitude response at all crossover
frequencies.
Please consult the manufacturer’s specifications of the various speaker components to set the crossover
frequencies. When polar plots of specific speakers or horns are available, use them too. Don’t set the
crossover frequencies around peaks or drop-outs in the frequency response, but try to find a range that is
largely linear. When folded woofer horns are used, you also need to take the horn length into account (see
chapter 3.5 “Runtime Correction”).
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Never operate speaker/horn drivers below the frequency range specified by the manufacturer!
3.5 Runtime Correction
3.5.1 Background
The ideal transducer would be a point source of sound, i.e. a speaker of infinitely small dimension, which
could still reproduce the entire frequency spectrum. Unfortunately, such a sound source is impossible in
reality, so that we have to accept some compromises.
If the drivers in a multi-way system (i.e. the diaphragm set in motion by the voice coil, but not e.g. the opening
of a horn) are not exactly aligned on a vertical axis, the varying distances between sound source and listener
result in phase errors and cancellations (also called “comb filter effect”). In particular, in the high-frequency
range it is imperative, due to the shorter wavelengths, that the drivers be positioned one above the other, not
side by side. The old-fashioned horizontal rows of radiators follow this principle: while the speaker power is
summed up in the horizontal plane, the signals cancel each other on a vertical axis. Thus, unwanted reflections
from the ceiling can be reduced.
Consequently, a speaker stack whose systems radiate towards the same area should have all speakers
arranged in a vertical line. And even if the front sides of all systems are perfectly aligned, runtime differences
still occur due to the different speaker designs (horns, bass reflex cabinet, etc.).
The BEHRINGER SUPER-X PRO allows you to delay the Low bands by up to 2 milliseconds. In this way, you
can virtually push back a specific speaker cabinet by as much as 68.6 cm (which is quite useful, for example,
when you place a constant-directivity horn (CD) on top of a closed speaker cabinet).
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Runtime correction is not the same as phase correction. Speaker systems that have the same
run times are also in phase (unless, the polarity of one speaker is reversed). However, the
opposite is not true.
3. APPLICATION