Martin Audio Wavefront W8CT, Application Manual

Page: 149 / 247

The listener hears the vector sum of more and more cabinets as he moves further
away from a straight line array. These increasing contributions partially compensate
for the normal reduction in sound pressure with distance from source.
Note that farfield spl levels will increase towards the centre of the array where more
elements add.
W8L Series
The classic explanation of line array behavior assumes omni-directional point source
drive elements that must be positioned within ¼ wavelength at their highest operating
frequency for coherent summation. Martin Audio designs comprise directional horn-
loaded sections. This closely coupled horn technique modifies the equations allowing
greater driver spacing. See our Institute of Acoustics, Reproduced Sound 2003 paper,
Advances in Line Array Technology for Live Sound.
Note that our mid and hf designs do not try to emulate a dead straight ribbon.
Practical loudspeaker columns must have vertical coverage patterns tailored to suit
the audience size and shape and our line array systems have been designed with this
in mind. The W8L Series are deliberately designed to produce slightly curved vertical
wavefronts - enough to allow up to 7.5º of vertical splay to be introduced between
boxes but not enough to affect straight line performance.
Progressive Curvature arrays
Straight columns (0º splay angles) produce far-field high-mid frequency sound
pressure levels that increase approximately 6dB for every doubling of W8L quantities
but, as inter-box splay angles increase, the vector sum of multiple W8Ls decreases
through 3dB for a 3º splay to 0dB (no summation) at 7.5º. This
Progressive
Curvature provides smooth level coverage without amplifier channel trimming for
most applications.
Martin Audio’s ViewPoint
tm
software calculates the optimum progressive curvature
for a given audience area. The progressive curvature produces a more consistent
frequency response from the front rows to the rear seats than often used J-shaped
arrays having a straight, long throw section at the top and a curved lower section. An
over-angular J-shaped array acts like a foreshortened straight array above a point
source array and creates vertical lobes that result in irregular coverage.
All material © 2007. Martin Audio Ltd. Subject to change without notice.