User Guide

Sound System Design Reference Manual
The rising DI of most typical radial horns is
accomplished through a narrowing of the vertical
pattern with rising frequency, while the horizontal
pattern remains fairly constant, as shown in Figure
3-8A. Such a horn can give excellent horizontal
coverage, and since it is “self equalizing” through its
rising DI, there may be no need at all for external
equalization. The smooth-running horizontal and
vertical coverage angles of a Bi-Radial, as shown at
Figure 3-8B, will always require power response HF
boosting.
3-7
Measurement of Directional
Characteristics
Polar plots and isobar plots require that the
radiator under test be rotated about several of its
axes and the response recorded. Beamwidth plots
may be taken directly from this data.
DI and Q can be calculated from polar data by
integration using the following equation:
DI = 10 log
2
P
θ
π
θθ
( )












∫
2
sin d
o
P
Θ
is taken as unity, and θ is taken in 10° increments.
The integral is solved for a value of DI in the
horizontal plane and a value in the vertical plane.
The resulting DI and Q for the radiator are given as:
DI =
DI
2
+
DI
2
hv
and
Q = Q Q
nv
⋅
(Note: There are slight variations of this
method, and of course all commonly use methods
are only approximations in that they make use of
limited polar data.)
Figure 3-8. Increasing DI through narrowing
vertical beamwidth