d&b 24C - Manual (Page 6)

2.1.3. Cardioid dispersion
Due to their dimensions, conventional column loudspeakers
provide no significant horizontal directivity below 2 kHz.
At low and mid frequencies, the resulting polar pattern is almost
omni-directional (dotted line).
The cardioid patterns of the 24C and 24C-E show a much higher
directivity resulting in much less energy radiated into the room
(continuous line).
Typically, column loudspeakers are mounted onto walls or other
hard plane surfaces. Hard surfaces act as an acoustic mirror. That
means, the room is not only covered by the sound of the actual
column loudspeaker but also by the sound produced by its virtual
mirror source from "behind".
In the case of conventional column loudspeakers with their low
horizontal directivity, the mirror source radiates at a similar level as
the loudspeaker itself.
The combination of both sources results in a dipolar characteristic
where the main energy is radiated along the walls (dotted line).
The 24C and 24C-E, however, with their cardioid dispersion
patterns provide an even dispersion characteristic and a useful
directivity when mounted onto a wall.
2.1.3.1. Flush mounting
If architecturally required, xC-Series cabinets may be partially flush
mounted.
Please note that this will render the cardioid ports ineffective and
as a result, may change the dispersion pattern.
In conjuntion with 24C cabinets, care must also be taken to ensure
that the dispersion of the rearmost horn of the HF array is not
obstructed by the edges of the wall recess. Otherwise, this will
create reflections which will have a negative impact on the
frequency response in front of the cabinet. The same applies when
the cabinet is mounted in a corner of the room. Reflections of the
adjacent side walls will cause deviations in both, the frontal
frequency response and the dispersion pattern.
d&b 24C/24C-E Manual 1.3 en 6