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Array, or not to array? That is the question

Mar 14, 2012 2:49 PM, By Bob McCarthy

Speaker considerations for best deployment.

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Figure 4: Response comparisons of a single speaker and four, 16, and 40 element arrays in the 4kHz range. From left to right: (a) Single speaker with 80° coverage (b) 4x20° speaker splayed at 20° (c) 16x10° splayed at 5° (d) 40x10° speakers at 2°. Coverage is always 80° but becomes sharper at the edges a quantity of elements increases. See larger image.


Arrays are the sum of their parts. There is plenty of buzz out there that could make one believe that arrays (especially line arrays) are an organism of their own with behavior that is only tangentially related to the original elements. Measuring a single element and then measuring it again in an array easily disproves this. The array behavior is multiplication and division of the original element response. More on this as we go.

First, let’s define exactly what an array is. An array is a configuration of two or more elements. A solo speaker that has “line array” printed on its grille is not an array, but a pair of cellphone speakers playing the same ring tone are. An array configuration is a relationship between elements. In practice, there are six basic array configurations, subdivided by two independent factors: angular orientation and displacement between elements. The relative angle can be outward (point source), inward (point destination), or parallel (line source). If the displacement is small, we have a coupled array that combines for power, such as a subwoofer and main arrays. If the displacement is large, we have an uncoupled array that combines for range extension, such as the spread elements of a frontfill array or a parade route. Each of the geometric planes is evaluated separately, so we could look at a close grouping of four boxes in a two-over-two configuration as a coupled point source in both planes. A straight line of frontfills, by contrast, would be an uncoupled line source in plane and a single element (not an array) in section.

When two elements of an array combine, one of three things happens: The coverage gets wider (multiplication), narrower (division), or breaks even. The decisive factor is the ratio of isolation versus overlap. If isolation between the elements is high (overlap is low), the sound spreads out. If isolation is low (overlap is high), the sound concentrates in the overlap region and the pattern narrows. If the two factors are equal, there is a stalemate and the pattern stays the same. The maximum overlap can cut the pattern in half and add up to 6dB of SPL. Maximum isolation can double the pattern width but won’t add level. In the land between these extremes, we find smaller changes in pattern shape and SPL addition.

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