The Obelisk Line Arrays




Designer: Shaun Bohannon

Project Time: 8-20 hours
Project Complexity: Hobbyist
Project Cost: $100-$500

Driver Selection
The driver choice for this project is a 3×5 inch full range driver from JVC. The driver’s size and extended frequency range of 90-16,000 make it an easy starting point for a budget line array. I chose to mount them in a vertical line of eight per speaker. This arrangement would allow for a narrow column on the order of four feet tall.

Enclosure Design
I examined many options enclosures and finally decided on 5×5 in. vinyl fencepost stock. An eight-foot section of post cut in half gave me the two 48’ sections I would need for the pair. I found using a fine-toothed metal jigsaw blade the holes for the speakers were very easy and quick to cut out. Following the measurements carefully was essential because of the combination of the narrow oblong baffles and the very close spacing required to maintain my line. Once the baffles were cut and the drivers mounted I capped each tower with a 5×5 pointed fence cap and fashioned a base for each from pre-cut wooden plaques available from any craft store. Three pieces of 2×4 lumber were cut and glued together to form a post for the tower to slip onto, these are mounted in the center of each plaque. They are finished with Dayton

Amplifier/Crossover Configuration
To begin with I wired the enclosures with no crossover of frequency shaping of any kind. They were each initially wired as a full range 4-ohm speaker using the series-parallel wiring scheme shown below. Later I decided to rewire the cabinets to be 16-ohms each to better fit the intended amplifier. To keep the design simple I decided not to implement any sort of passive high pass filter. One could easily be added to help protect the speaker from overdriving the lower frequencies at high volumes if desired.

Conclusion
For use in the home as a stereo system the Obelisk’s performance is lively with music and movie material. I feel no need for dedicated high frequency drivers (though I did test the Obelisks with multiple tweeters just examine the difference). Low frequency extension is surprising from an array consisting of nothing larger than effectively 4” drivers, but I still felt the need to hand off bass duties below 150hz to a subwoofer for best results. I also tested the pair (in their 4-ohm configuration) in a 120-seat auditorium and was pleased with the ease with which they filled the space. Even one speaker was enough to cover the auditorium for microphone use or for music. Driven by a 100 watt PA amplifier they were able to project sound well over 200 feet and were easily heard outside the auditorium at one quarter volume.


Project Parts List

JVC 3″ x 5″ Full Range Driver

Dayton Audio DSS2-SN Satin Nickel Spike Set 4 Pcs.

Rean NYS2122 1/4″ Mono Jack Switched

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