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Array A5
Application Notes
A sometimes unanticipated problem in sound system design is excessive low frequency energy
beneath the flown array. Related to this can be poor low frequency coverage into the audience
area and a system with excessive ‘lobing’ onto the performance area. This is usually caused by
arranging low frequency devices in such a way they do not work together in an efficient
manner.
A single low-frequency device by itself has very little directivity. However, by spacing a pair of
low frequency devices the resulting ‘spaced-source’ array has a directivity defined by the
distance between the devices and the frequency. Additionally, spacing the drivers above and
below the MF waveguide has the effect of extending the effective working height of the system,
thus allowing the resulting array to work together smoothly through a lower frequency. This is
commonly known as a bipole array.
Not only will this reduce LF energy on the stage, thus increasing gain before feedback, it will
also have the effect of improving the evenness of coverage in the audience area.
The diagram below (Fig 1.) describes how the levels of the loudspeaker system must be
controlled in the vertical plane to achieve consistent direct levels in the seating area.
To achieve the spaced-source effect, a PD5122 is simply placed below a standard PD5322. The
low frequency device spacing creates a directivity pattern that essentially matches that of the
mid-frequency waveguide. The result is a smooth transition in directivity performance through
crossover.
Since the PD5122 is simply the LF section of a PD5322, the response of the LF sections will be
identical and they can utilize the same DSP processing settings. No additional steps are required
to realize the increased vertical directivity offered by this array configuration. Refer to JBL
Tech
Note V1 #32
for additional information and polar data concerning this array.
Fig. 1: Section Drawing
