Making It Directional
As previously noted, a primary goal is keeping excessive LF energy out of areas where we don’t wish it to be. With select placement/arrangement of subs and the application of processing such as signal delay, various radiation patterns can be attained.
Some of the more popular directional array techniques include:
Delay Shaded Array. This reduces the output of the boxes at or near the ends of an array (like a horizontal array), with the intent to make the coverage pattern more regular and less frequency dependent.
Cardioid Array. Two popular cardioid approaches are stacking and side by side. Stacking places the boxes on top of each other, with one cabinet (usually the middle cabinet in a stack of three) reversed to point to the rear. Side by side places the boxes next to each other and reverses one (again normally the middle one of three).
Further pattern control can be attained by applying delay, either by delaying the output of the front-facing cabinets to arrive at the same time as the output of the rear-facing cabinet, or by delaying the rear-facing cabinet to the output of the front-facing cabinets while also reversing the polarity of the rear-facing cabinet so that it’s signal is 180 degrees out of phase with the front-facing cabinets.
End Fire Array. Multiple cabinets are aligned in a row, arranged one in front of the other with all pointing forward. All cabinets are delayed in relation to the rear-most cabinet. This approach makes it possible to project powerful, directional bass over long distances. Figure 6 shows how an end fire array provides very good pattern control at 80 Hz.
Obviously, there’s a lot to discuss when it comes to subwoofers, and what I’ve presented here is intended as a primer, really just scratching the surface.
I recommend further research to enhance your understanding—for example, ProSoundWeb offers dozens of articles on subwoofers and related topics, while the LAB Subwoofer Forum on PSW is an excellent resource for both information and getting questions answered.
It’s well worth your time, as delivering LF energy with maximum impact and control is one of the defining factors of a successful sound reinforcement experience.
Senior contributing editor Craig Leerman is the owner of Tech Works, a production company based in Las Vegas.