Cardioid subwoofer arrays: putting low-frequency energy where the audience is
Abstract. A subwoofer on its own radiates in every direction, and at low frequencies walls and stages offer no shelter. This note explains how driving front and rear sections with controlled delay and polarity produces a cardioid pattern, and what that buys on stage, off site and in the audience.
Why subwoofers are omnidirectional
A source is directional only when it is large compared with the wavelength it radiates. At 50 Hz the wavelength is nearly seven metres, so any practical cabinet is acoustically small and radiates essentially omnidirectionally. The energy that reaches the audience is matched by energy sent onto the stage, into the structure and toward the neighbours, and no enclosure shape changes that on its own.
The cardioid mechanism
Directionality at low frequency comes from arrays, not boxes. Place a second source behind the first at a spacing d, delay it by the time sound takes to travel d, and invert its polarity: behind the array the two arrivals align in time and opposite in sign, cancelling, while in front they arrive spread in time and sum constructively. The result is the cardioid family of patterns, with deep rejection behind and modest change in front.
The same result can be had from front and rear drivers in one cabinet or from separate cabinets in a ground stack; the physics is identical. The rejection depth depends on how precisely level, delay and polarity are matched across the band, which is why cardioid operation is implemented as DSP presets driving dedicated sections rather than as a wiring trick.
What CardioSteer is for
CardioSteer is the preset family that drives SSOUNDS front and rear low-frequency sections with the delay and polarity relationships above. The intended results are practical: less low-frequency energy on stage means cleaner microphone conditions and less energy re-entering the system; less energy behind the site eases compliance with off-site noise limits; and removing the rear radiation that would otherwise reflect back through the audience tightens low-end definition where listeners actually stand.