JBL Technical Note - Vol.1, No.32 电路原理图.pdf

The Precision Directivity PD5000 family of products offered by JBL Professional is a ver- satile product line allowing a sound designer numerous ways to implement arrayed solutions for houses of worship, performing arts centers, and sports facilities. The compact design of the PD5000 models provides excellent array characteristics both acoustically and aestheti- cally. This application note specifically focuses on how two of the models, the PD5322 (three- way, full-range) and the PD5122 (dual 12” slot loaded low-frequency), can be used individual- ly or in combination to create array solutions Technical Notes Volume 1, Number 32 Title: Basic PD5322 and PD5122 Array Applications addressing common design requirements. A sound designers objective is to design a loud- speaker system that provides consistent horizontal and vertical pattern control through its usable fre- quency range.This achieves an even spectral bal- ance throughout the seating area and excellent microphone gain before feedback. The diagram below (Fig 1.) describes how the levels of the loud- speaker system must be controlled in the vertical plane to achieve consistent direct levels in the seat- ing area. FIG. 1: SECTION The following examples show how directivity can be maintained in the vertical plane by uti- lizing methods that create a smooth transition between the polar responses of the mid-fre- quency waveguides and the low-frequency devices. A waveguide by itself is limited to how low in frequency it can control pattern based on the dimensions of the waveguide and the nominal coverage.1For pattern control below 800 Hz, the size of a single waveguide becomes too large to be practical in most cases. However, spaced-source low-frequency arrays provide effective and predictable polar responses that can be mated with the mid/high waveguides to produce integrated arrayed solutions that extend useful pattern control of the system to below 200 Hz.2 Example #1, PD5322+PD5122 A PD5322 consists of dual 12” VGC Vented Gap Cooled LF drivers, one on either side of the high-frequency waveguide and directly above the mid-frequency waveguide. A match- ing pair of LF devices in the form of a PD5122 placed directly below the PD5322 MF wave- guide (Fig. 2) produces a spaced-source LF array effectively extending the height of the waveguide and correspondingly extending low- frequency pattern control through 160 Hz. The PD5122 is simply the LF section of a PD5322.The similarity insures that the response of the LF sections will be identical. The acoustical crossover between the low and mid-frequency sections is 250 Hz. In the verti- cal polar plots (Fig. 3), note how well pattern control is maintained through the system crossover. In a variation of this example, the same array configuration can be utilized to steer the main lobe of low-frequency energy down to provide smooth and controlled low frequency coverage closer to the stage. This result is achieved by offsetting the upper and lower low-frequency devices approximately 0.6 ms. (Fig. 4) id Fig. 3: PD5322 + PD5122 - modeled vertical polar response Fig. 4: Steered PD5322 + PD5122 - modeled vertical polar response A downfill box such as an Application Engineered AM6200/95 may be appropriate to maintain matching mid and high frequency energy below the main coverage pattern of the PD5322. Example #2,Vertically configured PD5322 pair In another variation, the same acoustic princi- ple can be realized by using a second PD5322 as a downfill device (Fig. 5), with the LF section on top of each of the two vertically oriented boxes. When the bottom box is splayed down at 30 degrees, as may be typical, the LF sections provide a spaced-source pair that extends the pattern control of the system similar to the previ- ous examples (Fig.6). In this example it is rec- ommended to low pass the lower pair of LF driv- ers at 125 Hz. This bandpass change is neces- sary because the LF pairs are spaced farther apart than in the previous example described. -3- PD5322/PD5122 App Note Fig. 5:Vertically configured PD5322s Fig. 6:Vertically configured PD5322 - modeled vertical polar response Example #3, Horizontally configured PD5322 pair For the same “long-throw/down-fill” combina- tion, two PD5322s may instead be stacked hor- izontally (Fig. 7). As a result, the four 12” low- frequency devices are placed on top of each other, making a short LF speaker column. This column exhibits desirable directivity and match- es the mid-frequency directivity at crossover. The coverage maintains the target directivity down to 250 Hz and remains useful through 160 Hz. (Fig. 8) Fig. 7: Horizontally Configured PD5322s Fig. 8: Horizontally configured PD5322 - modeled vertical polar response Fig. 9: Four-element PD5122 shaded array Fi10 PD5122 h d dd l dill Example #4, PD5122 shaded arrays: A simple 4-element shaded array may be con- structed with four PD5122s. (Fig. 9) Here, the two outer boxes are crossed over to the two center boxes at 140 Hz to create an array that matches the requirements of a typical space described above, and extends useful directivity past 125 Hz. (Fig 10) The shaded LF array could be part of a cluster consisting of PD700, PD5000, and AE mid-high loudspeakers. Fig. 10: PD5122 shaded array - modeled vertical polar response Fig. 9: Four-element PD5122 shaded array 140 - 250 Hz Summary: The PD5000 family provides elements to create effective arrays that are well behaved acousti- cally, maintaining pattern control into the low- frequency band. These types of arrays are use- ful for maintaining broadband evenness of coverage, especially in the vertical plane, with the added benefit of excellent micro- phone gain before feedback. REFERENCES 1.The Manta Ray Horns, Clifford A. Hendrickson and Mark S. Ureda, JAES, 1978 September. 2.Filtered Array Technology: A look at controlling an arrays low frequency radiation pattern using digital signal processing, JBL Professional Tech Note: Volume 1, # 28 Controlling Low Frequency Coverage via FSA Forward Steered Bass Arrays, JBL Professional A Harman International Company JBL Professional 8500 Balboa Boulevard Northridge, California 91329 U.S.A. 3/04 TN VOL. 1 NO. 32 COPYRIGHT 2004