CBT36K Assembly Manual
Page
84
of 89
The most straightforward way to implement the driver shading would be to drive each speaker in the array
with its own amplifier whose gain could be adjusted appropriately for each driver depending on its location
in the array. However, this is complicated and expensive. Fortunately from a practical standpoint, the
continuous shading can be approximated by dividing the drivers into multiple banks, each of which are
attenuated in a series of steps [7]. Furthermore, the attenuation of each bank can often be implemented
passively without requiring separate amplifiers for each bank.
The CBT36 uses 18 mid-woofers and 72 tweeters.
NOTE:
There are exactly four tweeters for each mid-
bass driver (4 x 18 = 72).
The 18 mid-bass drivers and 18 four-tweeter PC-board modules of the CBT36
are divided into five banks which are passively attenuated using series-parallel connection combinations
and resistive attenuators (the CBT36 schematics were shown earlier in the “Wiring” section of this
assembly manual).
The following table (Table 1) shows the five CBT36 mid-bass and tweeter banks along with their
attenuations:
Table 1: CBT36 Woofer and Tweeter Attenuation Banks:
Bank Number:
Attenuation:
Mid-Bass:
Tweeters:
1 (Bottom)
0 dB
6 Woofers, Drivers 1 - 6
24 Tweeters, Drivers 1 - 24
2
-2.5 dB
4 Woofers, Drivers 7 - 10
16 Tweeters, Drivers 25 - 40
3
-4.5 dB
4 Woofers, Drivers 11 - 14
16 Tweeters, Drivers 41 - 56
4
-8.0 dB
2 Woofers, Drivers 15 - 16
8 Tweeters, Drivers 57 - 64
5 (Top)
-11.0 dB
2 Woofers, Drivers 17 - 18
8 Tweeters, Drivers 65 - 72
This shading method essentially approximates the continuous shading curve shown in the previous figure
with a series of steps [7] and is illustrated in the next figure. The graph shows the actual stepped shading
for the 18 mid-bass drivers with the attenuation shown for each bank. The attenuation levels of the
tweeters are exactly the same except there are four tweeters for each mid-woofer.
Fig. 37. CBT36 stepped-shading approximation (blue) of the continuous shading curve of the
previous figure (red). 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. The five bank attenuations are
respectively 0, -2.5, -4.5, -8.0, and -11.0 dB going from the bottom of the array to the top.
The next subsection shows a pictorial view of the CBT36 with side and front views indicating driver
shading banks and attenuations.
