CBT36K Assembly Manual
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(a)
(b)
(c)
Fig. 35. (a) A free-standing CBT line array with shading. (b) A ground-plane CBT line array
with shading. (c) A ground-plane CBT line array with acoustic reflection that essentially
doubles the size of the array.
14.2.8. Shading:
In addition to mounting the drivers on a circular arc, a CBT loudspeaker array requires shading or level
adjustment of each driver with respect to other drivers that make up the array. This maintains the best
coverage independent of frequency.
NOTE:
This shading or level adjustment is a simple fixed change of
volume of a particular loudspeaker and is independent of frequency. References [4] and [7] go into much
detail on the CBT shading.
The level adjustment or attenuation value for each driver depends on where the driver is located in the
array. For a free-standing array, the drivers in the center of the array are at a maximum while the drivers
at the outside of the array are attenuated.
For the CBT36 ground-plane array, the drivers on the bottom near the floor are turned on full and the
drivers at the top are attenuated the most. The drivers in between the bottom and top have intermediate
attenuation values.
The required theoretical shading values are illustrated in the following graph in a continuous curve. The
curve starts at 0 dB at the bottom of the array (left) and falls smoothly to -13.5 dB at the top of the array
(right). The bottom of the graph shows the location of the 18 individual woofers in the CBT36 array
numbered from 1 to 18 going from bottom to top. Details about this truncated Legendre shading method
are shown in reference [7].
Fig. 36. Theoretical Legendre truncated (-13.5 dB) continuous shading curve for a ground-
plane CBT array [4] [7-8]. The drivers at the bottom of the array (left) are turned on full while
the drivers at the top of the array (right) are fully attenuated.
