Fbt 38591, Operating Manual

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CARDIOID CONFIGURATIONS
Horiz. f=40Hz
H o riz . f= 1 3 0 H z , n o rm e d to 1
H o riz . f= 8 0 H z , n o rm e d to 1
The lack of directivity at low frequencies is a problem affecting many sound reinforcement systems: this directivity can be controlled by lining
up an array of direct radiation subwoofers according to patterns that concentrate diffused energy in one or more directions.
As for all frequency ranges, the sum of the energy of two subwoofers can lead to both 6dB sums and complete cancelling (when the sound
waves are 180° out of phase). The typical lobes of the polar diagram are caused by the difference in the time of arrival of sound sources to a
specific position.
Cardioid configurations are useful to cancel low frequencies from the stage and consequently to improve critical microphone recordings.
As you can see from the diagram, the attenuation achieved behind the front sound emission is 15 - 20dB approximately for the whole
subwoofer operating range ( 30 - 130Hz ).
The cardioid configuration enables a cardioid distribution of the SPL from subwoofers, reducing rear sound pressure. It is perfect when the
energy of low frequencies has to be attenuated, for example on the stage or in areas where it should be avoided due to noise pollution.
For this purpose, a rear sub shall be employed every two front subs. The majority of the enrgy generated by the rear sub is used to cancel the
energy of the other two front subs, so that the maximum overall SPL of the 3 subs in the front area is equal to +1dB approximately compared
to a typical (non cardioid) configuration with two front subs only. Obviously, this configuration is valid also with a front sub and a rear sub.
Subs position is very important in order to obtain the best possible rear attenuation. Use the configurations showed in picture.
-90° -90°
-75°
-105°
-60°
-120°
-45°
-135°
-30°
-150°
-15°
-165°
0°
+/-180°
+15°
+165°
+30°
+150°
+45°
+135°
+60°
+120°
+75°
+105°
+90° +90°
36 42 48 54 60 66 dB
36
PRESET ORIGINAL PRESET ORIGINAL PRESET ORIGINAL PRESET ORIGINAL
PRESET ORIGINAL
PRESET CARDIOID REAR
ORIGINAL 1 FRONT
PRESET CARDIOID REAR
ORIGINAL 2 FRONT
PRESET CARDIOID REAR
ORIGINAL 2 FRONT