User Guide

that the asymmetrical voicing produced by the axis asymmetric
design is a design compromise but it can be seen as less of a
compromise than that of the axis symmetric where the pattern
begins to narrow or the sonic performance of the drivers is
compromised because of using too low of a crossover frequency.
The second important parameter in line array design is
that of the minimum control frequency. We’ve discussed fmax,
the high frequency control that is limited largely by the spac-
ing b between devices. Discussion of fmin is also appropriate.
The low frequency control of the line array is dictated by the
physical height h of the array itself in Figure 34, Equation 5.
This is very analogous to the low frequency control of the
conventional horn related to its mouth height. Figure 34,
Equation 5 shows that fmin equals a constant over the product
of the required included angle and the height. As can be seen, f
min with a horn is related or is proportional to its overall
height. This is exactly the case for fmin with a vertical orienta-
tion of sources, or a line array.
ƒmin =
K
(included angle) (h)
Figure 35 shows the low frequency performance of a line
array related to its overall height. It shows both a multiple of
4 and a multiple of 5. This could be easily misconstrued that
the number of boxes controls the low frequency cut-off. This
is only indirectly the case. The actual parameter is the physical
height of the array, so large format, concert level line arrays
like the EV X-Line certainly require less boxes to get to a
particular cut-off frequency. The important thing to note from
Figure 35 is that if we average the 4 multiplier and 5 multiplier,
we see that a four box system in the case of a compact line
array (the XLC from Electro Voice) is limited to a 1,000 hz
control frequency, which relates to an overall line height of 58
inches. Frequently line arrays are presented that are 20 or 30
inches tall. These are certainly line arrays from a high frequency
standpoint, if the criteria is achieved to produce a full band-
width f max. Their ability to control the polar pattern at low
frequencies, however, is limited by their height. To achieve a
300 hz low frequency intercept, or fmin, the overall height
of the line array system needs to be roughly 203 inches.
Figure 35 is very instructive in terms of designing line arrays
to low frequency control limits.
An alternate way of looking at this chart and looking at
this parameter is seen in Figure 36. This shows the beamwidth
versus the frequency for a 58-inch high line array and a 116
high line array, doubling the height, as one would expect,
reduces, or improves the control by one octave. It is also
interesting to note that if one desires a 150 Hz line array
control, the line array must be 406 inches tall (almost 34 feet
tall), which certainly is taller than typical line array systems.
Figure 32
Figure 33
Figure 34, Equation 5
Figure 35
10