JBL Application Engineered Series Application Manual

Contents

-18-Array A5 Application NotesA sometimes unanticipated problem in sound system design is excessive low frequency energybeneath the flown array. Related to this can be poor low frequency coverage into the audiencearea and a system with excessive ‘lobing’ onto the performance area. This is usually caused byarranging low frequency devices in such a way they do not work together in an efficientmanner.A single low-frequency device by itself has very little directivity. However, by spacing a pair oflow frequency devices the resulting ‘spaced-source’ array has a directivity defined by thedistance between the devices and the frequency. Additionally, spacing the drivers above andbelow 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 iscommonly known as a bipole array.Not only will this reduce LF energy on the stage, thus increasing gain before feedback, it willalso 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 becontrolled 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. Thelow frequency device spacing creates a directivity pattern that essentially matches that of themid-frequency waveguide. The result is a smooth transition in directivity performance throughcrossover.Since the PD5122 is simply the LF section of a PD5322, the response of the LF sections will beidentical and they can utilize the same DSP processing settings. No additional steps are requiredto realize the increased vertical directivity offered by this array configuration. Refer to JBLTechNote V1 #32 for additional information and polar data concerning this array.Fig. 1: Section Drawing