Precision Directivity Speakers from JBL Professional

PD128

PD764

One of the challenges in large arenas, stadiums, houses of worship and performance spaces is to provide quality sound to every seat with the volume and clarity demanded by today's concert, sporting and special events. JBL Professional's new Precision Directivity (PD) line of speakers uses a full range, full bandwidth total system approach that allows contractors and consultants to design a fully integrated sound system that solves the audio challenges inherent to these types of large installations. JBL PD mid/high frequency loudspeakers utilize a new co-axial design, with specific coverage angles that allow the sound to be aimed precisely at individual sections of the audience area for high intelligibility and maximum fidelity. Another problems that PD technology solves is how to provide low frequencies (bass) evenly to every seat. JBL Engineering developed the new Precision Directivity technology that effectively allows the low frequencies to be "steered" at specific areas of the arena to assure even bass coverage throughout.

PD has progressed beyond the idea or prototype stage. Fully functional systems are already installed in high profile arenas and an outdoor sports facility. Once again, JBL is launching an important new product with a successful track record in prestige installations. At the 2000 AES Show in Los Angeles, JBL Professional introduced the VERTEC Line Array loudspeakers, which were successfully employed at the high-profile Democratic National Convention a month earlier. In late July, 2001, several months prior to this year's AES, the American Airlines Center in Dallas opened with its JBL sound system, which included several new PD designs.

"PD Series is the result of a fast-track development program by the JBL Custom Shop and JBL R&D in conjunction with some of our key customers and the Harman Professional Projects Group," explained JBL Professional President Michael MacDonald. "Last year, in discussions with the designers of several large arenas, we felt we had a new approach to help them design large speaker systems with predictable and manageable coverage patterns. Control and intelligibility are the results of the new PD Series."

Designers WJHW of Dallas and Impulse Group of Minneapolis were in the process of developing world-class sound systems for new arenas in Dallas and North Dakota. American Airlines Center and Ralph Engelstad Arena were destined to be premier, spare no expense arenas and the sound systems were required to meet very high standards. In each case, based upon early demonstrations of PD technology and the reputation of JBL and its Custom Shop, PD Series speakers were selected for these prestigious installations.

Seven models are being introduced. They are:

• PD162 - Mid bass array with six 12" drivers per enclosure
• PD162U4 - Mid bass array with four 12" drivers
• PD162L4 - Mid bass array with four 12" drivers
• PD125 - Dual 15" low frequency array
• PD128 - Dual 18" very low frequency subwoofer array
• PD743 - Co-axial mid/high frequency enclosure with 40° x 30° coverage
• PD764 - Co-axial mid/high frequency enclosure with 60° x 40° coverage

Low Frequency PD Systems

JBL Professional has developed three modular forward-steered low-frequency array systems. The PD162, with six 12-inch drivers per enclosure, reproduces the 125 Hz to 300 Hz upper-bass range. The PD 125 has two 15-inch drivers and is designed for low frequencies in the 50 to 250 Hz range. PD128, with two 18-inch drivers per enclosure, works in the 30 Hz to 125 Hz lower-bass range. Steerable arrays are formed by using individual enclosures in multiples and applying the proper signal processing. By having separate arrays for each of these low frequency bands, excellent audience coverage and off-axis rejection are achieved.

For the PD162 mid-bass arrays, the steering is accomplished by progressively delaying each pair of low-frequency transducers to a reference plane that is perpendicular to the direction in which the array is being steered. To maintain wide horizontal coverage, the array is kept as narrow as possible in that direction. In another unique design innovation, the transducers are mounted "motor out" to reduce the horizontal width of the array and to assist in cooling, which reduces power compression.

The PD125 works in a fashion similar to that of the PD162, but with a different mechanical configuration dictated by the larger size of its 15-inch drivers and their requirement for greater internal enclosure volume.

Due to longer wavelengths at frequencies where the PD128 Subwoofer Array operates and the larger enclosure volume required for response to 30 Hz, a different configuration is required. Greater spacing of the elements is necessary to effectively steer the energy since the wavelengths involved are longer. As with the upper-bass array, the lower-bass array is forward-steered by progressively delaying each set of modules. The two arrays can be used to compliment each other as they are optimized in their physical arrangement to effectively steer their main energy lobe and to accurately reproduce program in their frequency range. The result is powerful, coherent low frequency energy with optimized polar response.

The PD128 and PD162 are intended to work together to form the subwoofer/low frequency and mid bass sections of a four-way system when combined with PD Series mid/high enclosures. The PD125 forms the low frequency section of a three-way PD System for applications where the 30 Hz extension of the PD128 is not required.

Mid/High Frequency Enclosures

The PD764 60° x 40° and the PD743 40° x 30° devices are the first two mid/high Precision Directivity speaker systems. The audio requirements of stadiums and arenas such as Dallas' American Airlines Center require a new design for high-powered co-axial mid/high-frequency arena speakers using dual high-frequency drivers. Co-axial arrangements allow much smaller frontal area than the traditional designs with HF and MF elements adjacent to one another, which means mose compact arrays are possible. Since a co-axial design is inherently axis-symmetrical, the problem of an asymmetrical polar pattern caused by physical offset between mid and high frequency drivers is avoided. Before PD technology, physically large high-frequency drivers mounted in front of the midrange section have tended to partially obstruct the midrange sound, making this a compromised solution.

With the recent development of JBL's new compact, powerful 2430 compression driver, JBL determined that good-sounding, well-behaved high-output co-axial speaker systems could now be successfully developed. The driver is only 108 mm (4.25 in) in diameter and with its high energy neodymium magnet weighs less than three pounds. The very small cross-sectional area of the 2430 drivers allows the HF section to be acoustically transparent to the midrange wavefront.

To obtain the required midrange output, the system takes advantage of JBL's latest generation dual-voice coil Neodymium Differential Drive technology. The model 2250 high-power 400-Watt 8-inch transducer delivers the equivalent output of a 10-inch or 12-inch driver cone transducer, but with smaller size and lower moving mass that is preferable for midrange reproduction. This allows for closer driver spacing and results in a system with very high output with about half the distortion and less destructive interference than previous co-axial systems.

By using two of these high-output midrange drivers and two of the physically smaller, high-output compression drivers, the system is capable of long-term sound pressure level performance of 144 dB at one meter in both the high and mid-frequency bands or about 112 dB long-term average SPL at the typical arena's 120-foot throw distances.

PD Series speakers from JBL Professional are now in production.