Martin Audio W8L Longbow Application Manual page 16

Stacked general purpose horns vs low curvature line array elements
Note that individual elements have to be closely spaced to develop the benefits of a
line array. Stacking traditional, vertically formatted multi-driver cabinets (with,
typically, an LF driver near the bottom of the cabinet and an HF driver or horn near
the top) simply doesn't work.
The following illustrations compare the poor coverage characteristics of vertically
stacked general purpose loudspeakers with properly designed, closely coupled line
arrays elements.
The vertically spaced HF horns will have hot spots directly in front of each horn. The
outputs from these multiple elements will add or subtract in the mid and far field
depending on the wavelength and relative propagation times.
Three tightly arrayed low curvature horns at 8kHz
Closely spaced elements will sum more coherently.
As the number of coherent elements is increased forward projection strengthens and
the side lobes decrease.
All material © 2007. Martin Audio Ltd. Subject to change without notice.