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PLEASE
READ
CAREFULLY
BEFORE
PROCEEDING
GOING ONE STEP FURTHER IN LOW FREQUENCY CONTROL: RAY SUB TECHNOLOGY
Radiation control of low frequencies is hard to achieve due to wavelength being larger
than cabinet size. Consequently, most of current subwoofers available on the audio-
professional market are omnidirectional.
Drawbacks in using omnidirectional subwoofers are known by experienced engineers:
-
Low Frequency sound pressure level is typically higher on stage than over the
audience; high-pass filters are mandatory in almost all microphones inputs to avoid
feedback from the microphones to the subwoofers. Moreover, gain from microphone
to speakers is highly limited due to that feedback (reinforcing a double-bass can be
an enormous challenge);
-
Indoor environments typically have much higher reverberation time in the Low
Frequency range than in the mid and high Frequencies. This characteristic is
emphasized by the omnidirectional pattern of conventional subwoofers (all sound
engineers experienced kick drum lasting forever);
-
Many outdoor shows occur nearby residential areas where noise constraints are very
restrictive; in such cases, low frequencies levels over the audience have to be
limited so that environment criterias are fulfilled (possibly leading to unacceptable
wideband limitations).
Gradient subwoofers provide an elegant solution to the above issues, based on a
technology that is a simple transposition to sound sources of what has been applied for
decades in microphones: radiated field derives from pressure differences generated
from two (or more) sources:
-
Rear radiation is lowered by more than 12 dB, which benefits to stage as well as to
neighbours;
-
Direct to reverberant ratio is increased by nearly 6 dB in the low frequency range
(which potentially gives back a kick drum its original “punch”).
However, there are efficiency limitations: gain in lower bandwidth is reduced when
sources become too close in relation to wavelength, and pattern control is limited in
upper bandwidth when both sources interfere destructively in the radiation axis.
Operating bandwidth were efficiency combines with pattern control is around 2 octaves.
Poor correlation between cabinet design and targeted specifications leads to two (and
eventually more) drivers in directional mode producing less energy than one driver in
omnidirectional mode, which is not acceptable for simple practical aspects such as
weight and volume.
NEXO released its first gradient subwoofer – the CD12 – in 2002, which has been
complemented since then by CD18, GEO SUB and RS15. These have been quickly
adopted worldwide as standards, and are considered today as state of the art
subwoofers. This success is a consequence of proper cabinet design and optimized
definition of phase relations through sophisticated DSP algorithms leading to high
directional control and SPL output.
