This is the second part of our series focusing on subwoofers. The first and third parts are available here and here.
Woofer Array Types
In pro audio, we find three kinds of woofer arrays:
1. Broadside Arrays, in which a number of woofers are arranged in a row, and the primary radiation is at right angles to the row.
This is the typical subwoofer arrangement seen in most applications, either stacked (horizontal row) or flown (vertical row). In current practice, broadside arrays are overwhelmingly the most common form.
2. Gradient Arrays, in which woofers are arranged and driven in specific ways to provide microphone-like directional patterns—cardioid and hypercardioid, usually.
Such arrays involve woofers with multiple drive channels that may contain delays, filters, and/or polarity inversions to achieve their results.
Gradient arrays may be purchased as single enclosures, or can be constructed using separate woofer boxes.
3. Endfire Arrays, in which a number of woofer cabinets are arranged in a spaced row pointed in the desired direction of radiation, and driven in a successively delayed fashion so as to create a very narrow pattern.
The endfire array is the loudspeaker equivalent of a shotgun microphone.
Endfire arrays are rare, and are only useful in specific long-throw applications, outdoors or in huge venues.
A broadside array is a row of woofer boxes (or stacks of boxes) with the sound radiation more or less at right angles to the row. The row might be straight, curved, or staircased.
Broadside arrays are the most common woofer configurations, because they’re easy to design and set up.
However, getting good bass over a wide area requires some additions to the basic approach, as we shall see. Figure 9 through Figure 12 show some basic principles.
Figure 9 shows that long arrays have narrow patterns, while short arrays have wide patterns.