CBT36K Assembly Manual
Page
87
of 89
14.2.11. CBT36 Directivity vs. Frequency:
The following graph shows the simulated directivity of the CBT36 with frequency. Directivity is a measure
of the energy concentration in a particular direction compared to the total sound-energy radiated. The
graph shows that the directivity of the CBT36 is quite uniform above 200 Hz.
This indicates that the
CBT36 is a true broadband constant-directivity loudspeaker.
The following web links further explain the concept of directivity and how it applies to loudspeakers:
1)
http://en.wikipedia.org/wiki/Loudspeaker#Directivity
2)
http://www.linkwitzlab.com/Constant_directivity_louds.htm
3)
http://www.mcsquared.com/directvt.htm
Fig. 40. Simulated directivity vs. frequency of the CBT36. Note how uniform the directivity is
above 200 Hz.
14.2.12. CBT36 Power Rolloff:
One inherent characteristic of a circular-arc loudspeaker array is a power rolloff with increasing frequency
as compared to a straight-line array. In the case of a curved-arc CBT loudspeaker array, the power rolloff
is 10 dB/decade or 3 dB/octave throughout the frequency range where the vertical beamwidth is
controlled.
For the CBT36, this rolloff commences at about 200 Hz. The power rolloff is down about 10 dB at 2 kHz
and 20 dB at 10 kHz. This power rolloff must be compensated with corresponding lift equalization in the
DSP active crossover. The following graph shows the simulated power rolloff of the CBT36. Note that the
actual response curve of the active crossover includes the inherent responses of the system’s drivers.
Fig. 41. Simulated CBT36 power rolloff with frequency. This is an inherent characteristic of
curved loudspeaker line arrays in general and not just curved-arc CBT arrays. The rolloff
starts at 200 Hz and then falls at -10 dB per decade or 3 dB per octave throughout the
frequency range where the vertical beamwidth is controlled. This must be compensated by
corresponding lift equalization before the power amplifier.
