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Hookup Guide for CBT 70J-1 + 70JE-1 Array
The CBT 70JE-1 has the passive circuitry inside it to maintain the correct phase relationship
between the low-frequency drivers of itself and of the CBT 70J-1. The CBT 70JE-1's circuitry
also provides the correct frequency-band overlap characteristics so that the combination of the
two cabinets function as a proper line array with CBT (Constant Beamwidth Technology)
functioning. In addition, the built-in passive circuitry includes a complex multi-slope crossover
function. The end result is a column line array that is optimized, not only on-axis, but for all
off-axis points, for proper functioning.
Do Not Use an External DSP Crossover -- It is almost impossible to accomplish the proper
functioning described above in the field with an external DSP. In addition, you should NOT
use any crossover network between the cabinets because: a) the phase shift inherent in all
electronic crossovers (90 degree phase shift for every 6 dB per octave of slope) will put the low-
frequency drivers of one of the cabinets out of proper phase relationship with each other, b) you
wouldn't be able to accurately emulate the built-in multi-slope crossover, and c) depending on
how you set it, you could lose the required overlap characteristic between the two cabinets
which allows it to provide constant directivity control.
The Science -- The science of how the system works is something the installer and users don't
have to worry about and don't necessarily have to know. The important thing is simply that the
system is designed to work properly when you send the exact same full-range signal to both
cabinets in a CBT 70J-1/70JE-1 array.
However, if you want to know more about the science of why this is the case, here is some
simplified information about the functioning of the CBT 70J-1 and CBT 70JE-1 as a constant
beamwidth line array. In the CBT 70JE-1, the LF drivers operate from 45 Hz all the way up to
800 Hz. The LF drivers in the CBT 70J-1 operate over most of this entire range, too, as well as
going up higher in frequency. The reason that the CBT 70JE-1 drivers go up so high in
frequency (up to 800 Hz) is that the CBT 70J-1 by itself behaves as a line array that has a total
height of 70 cm (28 inches). Based on that height (and some other factors, such as the coverage
switch position), the vertical coverage typically starts broadening around 800 Hz.
One of the advantages of adding a CBT 70JE-1 is that is makes the array behave like a line array
that is twice as tall, or 140 cm (56 inches). This taller line array maintains the same pattern
control down to a much lower frequency. Therefore, it is necessary for all the drivers (in both
cabinets) to be operational throughout the entire frequency band, all the way from 800 Hz on
down. Unless the LF drivers in these two cabinets are in exactly the right phase relationship,
you could end up having the drivers in one cabinet cancelling out the sound from the drivers in
the other cabinet, either throughout the entire CBT 70JE-1 operational frequency band or at
some significant band of frequencies. Or, you could end up accidentally "steering" the LF
sound a certain direction upward or downward. Neither one of these is a good thing.
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