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About Cardioid Subwoofer Radiation
The term cardioid refers to a heart-shaped coverage pattern of an audio device. For example, a cardioid microphone is
most sensitive at the front (on-axis), and least at the rear (180 degrees off-axis). A cardioid subwoofer operates the same
way and is loudest at the front and quietest at the rear.
Low frequency energy from a conventional subwoofer is effectively omnidirectional below 200 Hz. This is because the
directivity of the subwoofer is related to the ratio of its size to the length of the sound wave it produces. The length of the
sound wave is inversely proportional to its frequency, and therefore when the low frequency waves are much longer than
the dimensions of the subwoofer transducer and enclosure, the radiation pattern becomes more equal in all directions,
including to the sides and back.
A cardioid subwoofer arrangement employs both front- and rear-firing woofers. Some clever use of spacing, delay, and
polarity produces cancellation in the rear-firing energy and reinforcement in the forward-firing energy. Historically, creating
cardioid subwoofer arrays has required the user to make complicated calculations involving physical spacing and signal
processing. Two QSC subwoofer models make those calculations unnecessary.
KS212C
The KS212C is powered by a dual 1800-watt Class D amplifier and incorporates dual 12-inch long-excursion drivers that
are each arranged in a sixth-order bandpass chamber. QSC’s latest DSP technology performs the complex processing
that makes these mirrored components interact at the rear of the enclosure to produce a desirable cancellation, while
simultaneously interacting at the front of the enclosure to produce equally desirable summation. As a result, the output
pattern is a cardioid shape, with 15 dB higher level at the front than at the rear. To put this into perspective, 15dB is
equivalent to the difference between 30 watts of power and 1000 watts.
KS118
The KS118 is a very high output active subwoofer, powered by a 3600-watt Class D amplifier driving a single 18-inch
direct radiating driver. Its on-board DSP menu offers the option of arraying two or more units in a forward/backward
cardioid arrangement with 15 dB of rearward rejection. From the subwoofers’ Cardioid menu, select Forward for the
units facing the audience and Rear for the ones facing away. This also allows side-by-side or ground-stacked setups.
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Typical
Rear
Cardioid
Rear
Subwoofer Energy Dispersion
FrontFront
– Figure 3 –
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General
Weight and Dimensions
