Handbook for Sound Engineers

Loudspeakers 613

radiator was used as the basis for predicting and
controlling the directivity of a horn.
Keele’s paper and horn designs provided impetus for
further empirical investigations of controlled directivity
horns. Altec Lansing, at that time a competitor of
Electro-Voice, introduced a family of horns using a
narrow, vertical diffraction slot located at an intermediate
point in the horn. With the appropriate choice of location
for this slot, it is possible to make a horn with any desired
combination of sidewall angles and aspect ratio (relation-
ship between the height and width of the mouth).
This family of devices was dubbed “Manta-Ray,”
and a number of designs based on this thinking were
introduced over the ensuing years, Fig. 17-31.
Another approach to achieving the goal of
frequency-independent directivity was represented in
the JBL biradial family of horn designs. Also devel-
oped by Don Keele, who had by then taken an engi-
neering position with JBL, the biradial shape employs
continuously varying flanges in both directions, ending
in a continuous horn. The vertical diffraction slot was
retained. An exponential expansion rate was part of the
design, and vertical and horizontal radial bell shapes
(thus the term biradial) were employed. Three biradial
horns are shown in Fig. 17-32. They are fabricated from
cast aluminum (throat section) and molded fiberglass
(bell section) and fit 2 inch exit drivers.

17.7.6.4 Voice Warning Horns

Fig. 17-33 shows another variety of controlled direc-
tivity horn, designed by Bruce Howze of Community
Professional Loudspeakers, and originally built for
Whelen Engineering. The horn used a slightly different
directivity control philosophy: a controlled horizontal
pattern (45° and a narrow vertical pattern), due to the

70 in (1.78 m) vertical dimension. The horn uses 16

siren drivers and the system, with a 1600 watt input,

generates 127 dB at 100 m (328 ft). It is used in a

similar manner to a searchlight: aim and shoot via a

remote rotor.

17.7.6.5 Asymmetric Directivity Horns

As the ability to determine the optimum loudspeaker

directivity requirements for specific applications was

refined, it became apparent that the required directivity

was usually not symmetrical about a horizontal plane

through the axis of the horn. From the point of view of

Figure 17-30. Electro-Voice HR9040 constant directivity

horn. Courtesy ElectroVoice, Inc.

Figure 17-31. Altec Lansing Manta-Ray horn family, cast

aluminum throat and soldered, coated bell construction.

Courtesy Altec Lansing Corp.

Figure 17-32. JBL biradial horn family cast aluminum throat

and fiberglass bell construction. Courtesy JBL/UREI.