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|7th December 2011, 09:21 PM||#1|
Join Date: Nov 2011
JBL 5234, Professional Series Frequency Dividing Network - AND and interesting story
For Sale -- JBL, Model 5234, Professional Series Frequency Dividing Network (two units)
These are two channel crossover networks that are set at 400Hz and 1.6kHz crossover points, 18dB/octave. This creates a pair (left - right) of three way audio channels bass to 400 Hz, Mid 400 to 1600 Hz, and high above 1600 Hz.
Removed from service into storage, excellent condition, NOT TESTED
If you are interested contact - Bobcul@nospam.locul.com to discuss the particulars
Now for the interesting part. These were used in a dance club sound system with Paired JBL bass folded horns with two 15' Cetec drivers each, two Cetec 10" K series instrument speakers in two splayed sealed direct radiating mid-range enclosures, and a Pair of Heil Air Motion Transformer (AMT) stacks for everything above 1600 Hz. Each stack was four units high. With the crossover frequency raised from 1kHz to 1.6kHz, and power divided into the four units, they stood up to heavy loading. Previously we had worked with ESS on the Heil AMTís through about five iterations of failure and redesign of the diaphragms and finally came up with the 25 Line, High Power Teflon, Bridal Vail Reinforced design.
Open field SPL mapping of various stack combinations of the AMTís showed a relatively narrow vertical high frequency beam pattern as expected with a broad horizontal pattern. The horizontal patterns were relatively constant with frequency. I still have the test data and plenty of photographs.
The AMT stacks were given about 10 degrees of mechanical down tilt. From their mounting point atop the base and mid range cabinets, they were above ear level on the dance floor. This produced a slightly attenuated level close in to the speakers, off to the side of the main vertical sound lobe, and increasing level at increasing distance as one moved away from the speakers and into the high frequency main beam.
Future work was anticipated, but never done, which would have been to frequency shape the power to the speakers. For example applying full spectrum from 1.6kHz cross over to high frequency cutoff to only one element, half bandwidth from low to about 8kHZ to a second element, and 1/4 BW from crossover to about 4kHz to all four elements. The goal would be to achieve a more uniform or better controlled vertical pattern. We still needed a narrow beam but perhaps the side lobes could be cut down.
This all analogous to RF and optics ;-)
Bob Culver, P.E.
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