Handbook for Sound Engineers

Stadiums and Outdoor Venues 209

and has a directivity that is almost identical to that of a
single structural element. The on-axis amplitude and
phase response is also that of a single constituent
device. For observation points off-axis, where T is no
longer zero, the amplitude response will exhibit a small
ripple as the frequency changes throughout the pass
band of the devices employed. The magnitude of this
ripple is inconsequential as it amounts to less than
1.25 dB. Perhaps of more importance is the behavior of
the phase response when observed off-axis. The phase
response ripples between plus and minus 90° as the
frequency changes throughout the pass band of the
devices that are employed. This ripple in phase response
is superimposed on the normal phase response of an
individual device. The mathematical details describing
the Bessel array behavior are given in the first reference
given at the end of this chapter. The Bessel array,
having preserved the coverage pattern of a single
device, is relatively insensitive to aiming errors
resulting from wind or thermal effects.
In recent years Meyer Sound Laboratories, Inc. has
produced a number of well-designed self-powered loud-
speaker systems that are well adapted for employment

in stadiums and outdoor venues. Even though the

concept of self-powered loudspeakers is an old one,

Meyer took the concept several technical steps further

by including not only the appropriate power amplifica-

tion but also the necessary signal processing, amplifier,

and loudspeaker protection circuitry as well, all within

the confines of the loudspeaker enclosure. One such

system that can be a real problem solver is Meyer’s

SB-1 sound beam loudspeaker system that is depicted in

Fig. 8-9.

The system of Fig. 8-9 is based on the properties of a

parabolic reflector. A parabolic reflector is really a

paraboloid, which is the shape generated when a

parabola is rotated about its principal axis. Such shapes

have been employed for many years as the basis for

reflecting telescopes, radar antennas, and microphones.

In the case of a telescope or microphone application the

paraboloid focuses a beam of light or sound emanating

from great distances to a common point known as the

focal point of the paraboloid. In the instance of a radar

antenna that is employed for both transmission and

reception, radiation from a small element located at the

focal point is formed into a parallel beam having small

divergence during transmission and return signals trav-

eling parallel to the system’s axis are focused on the

small element at the focal point during reception. In the

sound beam application of the SB-1 a 4 in compression

driver fitted with an aspherical horn is mounted in a

bullet-shaped pod and located at the focal point of the

paraboloid. This assembly is aimed at a fiberglass para-

bolic reflector having a diameter of approximately

Figure 8-8. Physical and electrical arrangement of simplest

Bessel array.

+ – – – – –

+

+

+

+ +

Figure 8-9. Meyer SB-1 Sound Beam. Used with the permis-

sion of Meyer Sound Laboratories, Inc.