Amate Audio X15D Manual De Usuario página 20

Passive Disco Systems
The typical operating range of a traditional subwoofer tends to be like a monopole,
i.e. tends to radiate with the same energy in all directions. This behaviour implies
that the control of radiation at low frequencies is very difficult because the
wavelengths are very large compared to the size of the source (8.5 m at 40Hz).
Fig.18. Cardioid pattern
7.1. The CARDIOID presets
X18D, X21D and X218D can generate an uncompromised cardioid behaviour when
used in conjuntion with an external Amate Audio DSP206/608 and their correct set-up
parameters.
In its minimum and standard configuration a Cardioid setup consists of a stack of
three subwoofer cabinets (for X18D and X21D) and of a horizontal line of three
subwoofer cabinets (for X218D).
Only one subwoofer is needed to compensate for the energy of the other two
radiating to the front. Then, the cabinet facing to the back (to the stage) should be
located in the centre of the column.
Fig.19. Cardioid configuration for X218D subwoofer
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To increase the directivity at low frequencies we
must transform the omnidirectional performance into
a cardioid performance. This can only be achieved
by various sources, arranged in a certain position, to
which we apply a specific phase, filtering and delay.
That is, we need to reproduce two signals with the
same frequency and similar amplitude which will
have a difference in phase of approximately 180º at
a certain point of the sound field. If the phases and
delays are well calculated the result is a system in
which we cancel the energy of the back and not the
one of the front.
Nov 2015
Amate Audio